W124 230E Thermostat Housing Sensors - How to Test?

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Ralf_CT
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W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Mon 03 Oct, 2016 4:46 am

I've got the South African spec W124 230E, the thermostat housing has four sensors:

1. One 3-pin;
2. One blue 2-pin;
3. One single-pin;
4. And a vacuum sensor controlling the vacuum advance.

A. What do (1), (2) and (3) control?
B. How does one test (1), (2) and (3)?
C. What should the readings be?

I connected an ohm meter across some of the the pins, and from the pins to earth but got no change in reading. I'm currently sitting with a poor cold and hot start problem (injectors and pressures have been checked, all okay), poor idling, vacuum gauge reads on the "retarded ignition timing" section. The issues basically manifested from one day to the next.

Many thanks.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Mon 03 Oct, 2016 8:08 am

1. One 3-pin;
This contains 2 Coolant Temp Switches, so is Open Circuit when Cold and Warm, but switches start operating when engine is Hot or Overheating. First switch kicks in @ 100degC, second @ 110degC.
Test by removing (have to drain Coolant to some extent) then heating carefully in Cooking Oil with a Thermometer whilst observing action of switches.
Here's a picture of the pins:
3-PIN_COMP.png
S25_4.png
That switch is unlikely to be cause of Cold Start problems.
This device contains 2 internal switches, so has two modes:
– When the Coolant reaches 100ºC, switches the Engine Fan on (the fan on the engine, behind the radiator, controlled by the Electro-magnetic Clutch). This is the normal cooling mode of the engine for long idling or heavy traffic when there is not much air movement through the radiator due to low speed, hot day etc etc.
– If the Coolant reaches 110ºC, switches the Auxiliary Fan on (the fan in front of the radiator) to Full Speed. This mode is to protect the engine from overheating damage e.g. if the Electro-magnetic Clutch engine fan fails, or Stirling Moss is driving the car hard, fast & furious on a hot day….

2. One blue 2-pin;
Mounted on Top of Thermostat housing, 2 wires with Round Connectors = Coolant Temperature Senders for EZL and KE Control Units.
On my car these both measure (resistance, one probe on (disconnected) sensor pin, other probe on Chassis/Engine) as follows:
Cold ~ approx 3600ohms
Warm ~ approx 600ohms (around 50deg on temp display in dash)
Hot ~ approx 330ohms (around 80deg on temp display in dash)

3. One single-pin;
Mounted on Side of Thermostat, pointing towards Distributor, single wire = Temp Sender for Coolant Temp Gauge in dash.
On my car this measures (resistance, one probe in sensor, other probe on Chassis/engine) as follows:
Cold ~ approx 1000ohms
Warm ~ approx 145ohms (around 50deg on temp display in dash)
Hot ~ approx 70ohms (around 80deg on temp display in dash)

4. And a vacuum sensor controlling the vacuum advance.
I think this is known as Thermovalve, and is normally closed. Opens at approx 50degC.

Hope that helps!
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Last edited by Christo C on Fri 08 Sep, 2017 8:11 am, edited 2 times in total.
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Mon 03 Oct, 2016 8:18 am

Christo C wrote:1. One 3-pin;
This contains 2 Coolant Temp Switches, so is Open Circuit when Cold and Warm, but switches start operating when engine is Hot or Overheating. First switch kicks in @ 100degC, second @ 110degC.
Test by removing (have to drain Coolant to some extent) then heating carefully in Cooking Oil with a Thermometer whilst observing action of switches.
Here's a picture of the pins:
Image

That switch is unlikely to be cause of Cold Start problems.
This device contains 2 internal switches, so has two modes:
– When the Coolant reaches 100ºC, switches the Engine Fan on (the fan on the engine, behind the radiator, controlled by the Electro-magnetic Clutch). This is the normal cooling mode of the engine for long idling or heavy traffic when there is not much air movement through the radiator due to low speed, hot day etc etc.
– If the Coolant reaches 110ºC, switches the Auxiliary Fan on (the fan in front of the radiator) to Full Speed. This mode is to protect the engine from overheating damage e.g. if the Electro-magnetic Clutch engine fan fails, or Stirling Moss is driving the car hard, fast & furious on a hot day….

2. One blue 2-pin;
Mounted on Top of Thermostat housing, 2 wires with Round Connectors = Coolant Temperature Senders for EZL and KE Control Units.
On my car these both measure (resistance, one probe on (disconnected) sensor pin, other probe on Chassis/Engine) as follows:
Cold ~ approx 3600ohms
Warm ~ approx 600ohms (around 50deg on temp display in dash)
Hot ~ approx 330ohms (around 80deg on temp display in dash)

3. One single-pin;
Mounted on Side of Thermostat, pointing towards Distributor, single wire = Temp Sender for Coolant Temp Gauge in dash.
On my car this measures (resistance, one probe in sensor, other probe on Chassis/engine) as follows:
Cold ~ approx 1000ohms
Warm ~ approx 145ohms (around 50deg on temp display in dash)
Hot ~ approx 70ohms (around 80deg on temp display in dash)

4. And a vacuum sensor controlling the vacuum advance.
I think this is known as Thermovalve, and is normally closed. Opens at approx 50degC.

Hope that helps!
Hi Christo, thank you for the detailed feedback, I'll study the info in the morning (our day is ending while yours is beginning). :)
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Mon 03 Oct, 2016 9:40 pm

Verdict:

1. Three-pin coolant fan/coupling switch:

a. With ignition on, bridging 12V and 100 activates electromagnetic coupling - OK.
b. Bridging 12V and 110 with a piece of wire does NOT activate the fan in front of the radiator. However, there is a 4.88V reading across 12V/110 leads coming to the switch. The fan used to come on, especially when idling in front of my garage on a hot day - last Friday I did however notice the engine getting hotter than normal in traffic. Maybe I should once again let it idle and see if the fan comes on (I don't think its operation is linked to the gas levels in the A/C as those currently seem to be low - no cooling with A/C on).

2. 2-pin coolant temperature sensor for KE Control Unit:

a. With the meter on 200, 2000 or 20k I get "1 .", no matter to which pin I connect the positive probe, with the other probe on ground. I assume the switch is shot, leading to my poor idling, cold start and hot start issues?
b. There's a 5.02V reading across the wires coming to the sensor.

3. 1-pin temperature gauge sensor:

The temperature gauge works, yet when connecting the probe to the pin I only get a brief reading. Running temperature is currently at 82 degrees, so I assume the switch is okay.

I'm concerned about the lack of readings on the 2-pin switch, and the 3-pin's 110 degree section (lack of activating the fan when bridging).
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Tue 04 Oct, 2016 4:59 pm

1. Three-pin coolant fan/coupling switch:
Only removing device and testing as I described will test the actual switches.

2. 2-pin coolant temperature sensor
Measuring the sensor resistances - did you do this with Ignition = OFF, wires to sensor disconnected, measure between sensor Pin and Chassis/Engine?
Resistance must be measured as above otherwise reading will be senseless.

3. 1-pin temperature gauge sensor
Same comments apply re measuring resistance.
But seems this sensor is fine since you gauge works....
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Tue 04 Oct, 2016 5:18 pm

Christo C wrote:1. Three-pin coolant fan/coupling switch:
1. Only removing device and testing as I described will test the actual switches.

2. 2-pin coolant temperature sensor
Measuring the sensor resistances - did you do this with Ignition = OFF, wires to sensor disconnected, measure between sensor Pin and Chassis/Engine?
Resistance must be measured as above otherwise reading will be senseless.

3. 1-pin temperature gauge sensor
Same comments apply re measuring resistance.
But seems this sensor is fine since you gauge works....
1. Agreed, but if one removes the connectors, switches on the ignition and bridges the 12V and 110 leads shouldn't the electric fan engage (the electromagnetic coupling does)?
2. Yes, wires disconnected. Ignition on and off, pin to chassis readings are the same (none).
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by ChristoC » Tue 04 Oct, 2016 8:33 pm

> 1. Agreed, but if one removes the connectors, switches on the ignition and bridges the 12V and 110 leads shouldn't the electric fan engage (the electromagnetic coupling does)?
- Yes that should engage front fan. If yours is asme as mine that could be bad relay up behind fuses or bad fan or wiring fault.

> 2. Yes, wires disconnected. Ignition on and off, pin to chassis readings are the same (none)
- If you trust your meter then this sensor is likely cactus.


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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Tue 04 Oct, 2016 8:47 pm

ChristoC wrote:> 1. Agreed, but if one removes the connectors, switches on the ignition and bridges the 12V and 110 leads shouldn't the electric fan engage (the electromagnetic coupling does)?
- Yes that should engage front fan. If yours is same as mine that could be bad relay up behind fuses or bad fan or wiring fault.

> 2. Yes, wires disconnected. Ignition on and off, pin to chassis readings are the same (none)
- If you trust your meter then this sensor is likely cactus.


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1. Now that you mention the relay, could it be that the electric fan only runs when the engine is running? Maybe I should remove the connectors, start it and then bridge the 12V and 110 contacts on the leads.

2. The meter is an el-cheapo, but I've used it successfully on my bike and one doesn't really need a high-priced Fluke to measure 300 - 2,800 ohms. The switch is unavailable at the dealers in SA, only ex-Germany.

I'm wondering if there will be a hug improvement with a new sensor. At this point the idling, start-ups and performance are poor. Fuel consumption +-11.5l/100. When I connect a vacuum gauge it claims the "timing is retarded", possibly a limp-home mode set by the ECU because it's not getting the correct coolant temperature (well, in my case it's not getting anything).
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 05 Oct, 2016 1:15 am

Someone suggested a Topran aftermarket switch. I've just returned from the dealer, tested their Topran unit and got the same results as with mine (no readings!). It can't be my tester. If I, for example, set it to 200 ohms the gauge reads "1 .", if I touch the two probes together I get "00.5". So it's probably safe to assume the Topran unit, which costs 85% less than the MB unit, is also faulty.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Wed 05 Oct, 2016 6:53 am

Reading back through this, earlier you said your meter only gave a brief reading on 3. 1-pin temperature gauge sensor.
Yet the Temperature gauge seemingly works....
Therefore suspect the meter so I suggest at least try another resistance meter on both 2. 2-pin coolant temperature sensor & 3. 1-pin temperature gauge sensor.

BTW 2. 2-pin coolant temperature sensor is not a "switch" - it is a sensor which varies it resistance with temperature. (correctly, a device with negative temperature coefficient)
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 05 Oct, 2016 7:41 am

Christo C wrote:Reading back through this, earlier you said your meter only gave a brief reading on 3. 1-pin temperature gauge sensor.
Yet the Temperature gauge seemingly works....
Therefore suspect the meter so I suggest at least try another resistance meter on both 2. 2-pin coolant temperature sensor & 3. 1-pin temperature gauge sensor.

BTW 2. 2-pin coolant temperature sensor is not a "switch" - it is a sensor which varies it resistance with temperature. (correctly, a device with negative temperature coefficient)
Agreed, I'll remove the NTC sensor and take it down to my local auto electrician to check on his meter.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 05 Oct, 2016 7:13 pm

Ralf_CT wrote:
Christo C wrote:Reading back through this, earlier you said your meter only gave a brief reading on 3. 1-pin temperature gauge sensor.
Yet the Temperature gauge seemingly works....
Therefore suspect the meter so I suggest at least try another resistance meter on both 2. 2-pin coolant temperature sensor & 3. 1-pin temperature gauge sensor.

BTW 2. 2-pin coolant temperature sensor is not a "switch" - it is a sensor which varies it resistance with temperature. (correctly, a device with negative temperature coefficient)
Agreed, I'll remove the NTC sensor and take it down to my local auto electrician to check on his meter.
I've removed the sensor. When checking across the terminals with my meter I now get "4.68" on the 20k scale, a brief "1,950/950" flicker on the 2000 scale and "1 ." on the 200 scale (previously it remained at "1 .", no matter what scale). Does this mean 468 ohms at room temperature, or 4,680? If the former, then the ECU always thinks the engine's hot, if the latter then it basically corresponds to a 5 degree engine temperature.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Bartman4800 » Wed 05 Oct, 2016 7:40 pm

It means 4.68 kOhm, which is the same as 4680 ohm

Bart
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1960 220 Sb Sedan "Zum Schlachten" (Early German Assembly, with a torsion bar spring for the bonnet) - Stored in Country WA
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2002 VW Passat V6 30V Station Wagon (SOLD - This car into a money pit)
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W124 230E Thermostat Housing Sensors - How to Test?

Post by ChristoC » Wed 05 Oct, 2016 8:04 pm

Now the figures I originally posted for "cold" were for a cold engine in Sydney during a summer day; ambient temp maybe around 25-30degC; thus will vary if you are in a cooler climate!
Around 4000ohms seems in the ballpark to me and chances are it's OK.
Question is does the resistance decrease say if you dip sensor for a few minutes into hot water (cup of tea)?


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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 05 Oct, 2016 9:54 pm

ChristoC wrote:Now the figures I originally posted for "cold" were for a cold engine in Sydney during a summer day; ambient temp maybe around 25-30degC; thus will vary if you are in a cooler climate!
Around 4000ohms seems in the ballpark to me and chances are it's OK.
Question is does the resistance decrease say if you dip sensor for a few minutes into hot water (cup of tea)?


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Yes, decreases to around 500-600.

Now that that's working I've still got the uneven idle - varies by +-50RPM either way in neutral (A/T), otherwise performance okay. Cold and hot starts are still not ideal - cold start not as 'crisp' as it was two weeks ago; brief misfire on a hot start for about 2 seconds. Injectors all okay, no pressure drop, no dribbling, no leaking cold-start injector; pressures: 2.8kPa resting, 5.8kPa with the pump bridged.

Oh, the electromagnetic fan and electric fan are all okay, engaging/disengaging with the engine running at around 100/110. It seems the electric fan does go via one of the system relays (fuel pump etc.), only working with the engine running.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Bartman4800 » Thu 06 Oct, 2016 11:30 am

Ralf,

Could the varying idle be caused by an air leak in the intake circuit? Spray a bit of carby cleaner around the intake manifold when engine is running, see if that makes a difference.
Could also be a vacuum hose to the gearbox?


Bart
1963 220 Sb Sedan "Kermit" (Australian Assembly)
1960 220 Sb Sedan "Zum Schlachten" (Early German Assembly, with a torsion bar spring for the bonnet) - Stored in Country WA
1981 Subaru Brumby 1.8 with Weber and 5-speed box "little utie" - Sold to another enthusiast!
2006 Ford Focus "daily driver"
2002 VW Passat V6 30V Station Wagon (SOLD - This car into a money pit)
2011 Kia Sportage "Missus commuter Bus"
2002 Mitsubishi Rosa Bus (converting it to a motor home)

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 09 Nov, 2016 3:17 am

Ralf_CT wrote:
Christo C wrote:1. One 3-pin;
This contains 2 Coolant Temp Switches, so is Open Circuit when Cold and Warm, but switches start operating when engine is Hot or Overheating. First switch kicks in @ 100degC, second @ 110degC.
Test by removing (have to drain Coolant to some extent) then heating carefully in Cooking Oil with a Thermometer whilst observing action of switches.
Here's a picture of the pins:
Image

That switch is unlikely to be cause of Cold Start problems.
This device contains 2 internal switches, so has two modes:
– When the Coolant reaches 100ºC, switches the Engine Fan on (the fan on the engine, behind the radiator, controlled by the Electro-magnetic Clutch). This is the normal cooling mode of the engine for long idling or heavy traffic when there is not much air movement through the radiator due to low speed, hot day etc etc.
– If the Coolant reaches 110ºC, switches the Auxiliary Fan on (the fan in front of the radiator) to Full Speed. This mode is to protect the engine from overheating damage e.g. if the Electro-magnetic Clutch engine fan fails, or Stirling Moss is driving the car hard, fast & furious on a hot day….
Hi Christo, could you please check on your car if bridging the terminals on the 110 degree side of your switch activates the auxiliary fan. On mine bridging the 100 degree side activates the electromagnetic clutch (as it should), but nothing happens when I bridge the 110 degree side. In stop-start traffic the car's running hotter than normal and the main auxiliary fan no longer comes on as it used to (my A/C gas is low but the compressor still cuts is - as far as I know the auxiliary fan is not dependent on a signal from the A/C pressure switch, it's only purpose is to provide additional cooling). If yours comes on when bridging then I know my switch is faulty.

Many thanks!
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Wed 09 Nov, 2016 6:42 am

Yes, bridging the terminals on the 110 degree side of the 3-pin switch activates the auxiliary fan M4 (on front of radiator) at FULL SPEED.
This is achieved through 'single contact' relay K9 (mounted up near the fuses), which switches the aux fan M4 on without the limiting resistor.

> If yours comes on when bridging then I know my switch is faulty.
Actually, if yours doesn't work when bridging the +12 & 110deg terminals it could be the K9 relay or wiring, not the switch.

The A/C pressure switch S32 simultaneously switches the same aux fan M4, but only to HALF SPEED through the big resistor R15 (mounted down near the Receiver/Dryer), AND the Electromagnetic Clutch Fan Y2, using the "double contact" relay K8 (also mounted up near the fuses).

Here's a circuit:
Image

Red wiring = +12V
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 09 Nov, 2016 6:09 pm

Christo C wrote:Yes, bridging the terminals on the 110 degree side of the 3-pin switch activates the auxiliary fan M4 (on front of radiator) at FULL SPEED.
This is achieved through 'single contact' relay K9 (mounted up near the fuses), which switches the aux fan M4 on without the limiting resistor.

> If yours comes on when bridging then I know my switch is faulty.
Actually, if yours doesn't work when bridging the +12 & 110deg terminals it could be the K9 relay or wiring, not the switch.
Thank you Christo, you're a great help as always! So, theoretically I should hear the K9 relay click when bridging the +12 and 110deg terminals? There's only one problem, when previously checking the supply I only measured 4.88V across 12V/110 leads coming to the switch (maybe this is all the relay needs?). As mentioned, the electromagnetic clutch works fine with the 4.88V.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by ChristoC » Wed 09 Nov, 2016 6:25 pm

4.88V seems way too low!
Check fuse D & 7 connections (could be corrosion there) and wiring.
Possibly block to chassis earth too (check that by measuring voltage between switch +12 and block, then between switch +12 and battery negative terminal; if substantially different suspect block to chassis "ground" connection).


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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 09 Nov, 2016 7:11 pm

ChristoC wrote:4.88V seems way too low!
Check fuse D & 7 connections (could be corrosion there) and wiring.
Possibly block to chassis earth too (check that by measuring voltage between switch +12 and block, then between switch +12 and battery negative terminal; if substantially different suspect block to chassis "ground" connection).


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Is the supply not regulated by the ECU (similar to the K-Jetronic coolant sensor and cold start valve), that may explain the 4.88V?
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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W124 230E Thermostat Housing Sensors - How to Test?

Post by ChristoC » Wed 09 Nov, 2016 8:18 pm

On my car, as in the circuit above, fuses D & 7 are +12v via ignition switch, not ECU.
Good idea to check voltage at both fuses.


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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Thu 10 Nov, 2016 1:17 am

ChristoC wrote:On my car, as in the circuit above, fuses D & 7 are +12v via ignition switch, not ECU.
Good idea to check voltage at both fuses.

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Christo, you won't believe it, fuse 'D' was broken, rather than blown!

I measured 12.25V across the 100°C plug terminals, and 7.65V between the 110°C plug and earth (rising to 8.65V with the engine idling) - these values remain the same for both, even with the first 5-pin and the second 6-pin relays behind the fuse box removed. There was no voltage at 'D' with the ignition on, and the auxiliary fan didn't cut in when the respective terminals were bridged, but it DOES cut in at +-110°C with the engine idling - I didn't check fuse '7', it must be okay as all accessories covered by it work. As mentioned above, the electromagnetic clutch cuts in (even with both relays removed). Bridging '30' and '87' with the first 5-pin relay removed activates the auxiliary fan.

Looking at your diagram, there should be no power in the cable coming to the single 110°C plug, yet I'm measuring 7.65V between this and earth (even with both relays removed)?
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Thu 10 Nov, 2016 6:53 am

> > As mentioned above, the electromagnetic clutch cuts in (even with both relays removed).
That is correct: looking at the diagram: terminal X26 supplies +12v (from fuse 7) to the common terminal of 3-pin Temp switch S25/4; when the 100deg switch closes +12v is switched direct to electromagnetic clutch Y2,.... relays not involved here.

> > Bridging '30' and '87' with the first 5-pin relay removed activates the auxiliary fan.
Not sure which are terminals '30' and '87', however that is a good sign the fan works, but I suspect possibly the relay may be cactus... see below...

> > Looking at your diagram, there should be no power in the cable coming to the single 110°C plug, yet I'm measuring 7.65V between this and earth (even with both relays removed)?
Are you using a Digital Volt Meter (DVM) ? - in which case there's probably some induction in the wires - DVMs have an incredibly high input impedance so will often show induction voltages present on un-terminated wiring - with the relay removed there is (hopefully) nothing connected to the wire at all, but it runs past plenty of other "hot" wires (especially at the fusebox end) where induction can occur.
As Tom Jones said, "it's not unusual" to get spurious voltage readings with DVMs.
Try using an old-school D'Arsonval (moving coil) volt meter, OR connect a load (small light globe) across the line whilst taking measurement with DVM.
With the relay out you can measure the coil's resistance across 2 of it's terminals.... it should be low @ around 50-150 ohms (exact resistance unknown, just as long as it is low rather than thousands or tens of thousands of ohms which indicates open circuit).
If you re-insert the relay K9 you should be able to read the same low resistance to chassis at the 110deg wire - if not, the relay's coil is possibly open circuit (cactus) or there's a broken wire somewhere.
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Thu 10 Nov, 2016 7:41 am

Christo C wrote: > > As mentioned above, the electromagnetic clutch cuts in (even with both relays removed).
That is correct: looking at the diagram: terminal X26 supplies +12v (from fuse 7) to the common terminal of 3-pin Temp switch S25/4; when the 100deg switch closes +12v is switched direct to electromagnetic clutch Y2,.... relays not involved here.

> > Bridging '30' and '87' with the first 5-pin relay removed activates the auxiliary fan.
Not sure which are terminals '30' and '87', but I suspect relay may be cactus... see below...

> > Looking at your diagram, there should be no power in the cable coming to the single 110°C plug, yet I'm measuring 7.65V between this and earth (even with both relays removed)?
Are you using a Digital Volt Meter (DVM) - in which case there's probably some induction in the wires - DVMs have an incredibly high input impedance so will often show induction voltages present on un-terminated wiring - with the relay removed there is (hopefully) nothing connected to the wire at all, but it runs past plenty of other "hot" wires (especially at the fusebox end) where induction can occur.
As Tom Jones said, "it's not unusual" to get spurious voltage readings with DVMs.
Try using an old-school D'Arsonval (moving coil) volt meter, OR connect a load (small light globe) across the line whilst taking measurement with DVM.
With the relay out you can measure the coil's resistance across 2 of it's terminals.... it should be low @ around 50-150 ohms (exact resistance unknown, just as long as it is low rather than thousands or tens of thousands of ohms which indicates open circuit).
If you re-insert the relay K9 you should be able to read the same low resistance to chassis at the 110deg wire - if not, the relay's coil is possibly open circuit (cactus) or there's a broken wire somewhere.
True, I should've seen that '7' supplies power to both the 100 and 110 side, while the 110 side switches the relay which then sends power to the auxiliary fan via 'D'. I'll check the relay coil tomorrow (it must be working because the auxiliary fan cuts in and out, but not when I bridge the wires at the switch with the ignition on - suspect). Actually, now that I think about it, I seem to recall the front (aux fan) relay clicking when I re-inserted it with the ignition on but engine cold. That basically means something, other than the 110 switch, is energizing the coil, but then the aux fan should be running continuously? Something's not right here.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Thu 10 Nov, 2016 8:10 am

Your car may well differ from mine (7 years difference), though I can't imagine by much; however the relay behaviour you describe does seem odd....
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Thu 20 Jun, 2019 9:14 pm

Christo, in an earlier post above I mentioned the 16A fuse blowing after the Aux fan had come on a few times (at the time both the Aux fan and electromagnetic clutch were working). This seems to have stopped, possibly due to the electromagnetic fan no longer switching on (it works when the contacts are bridged so I assume it's the switch). Do the Aux fan and electromagnetic clutch share the 16A fuse, that would explain why the lower current load is not blowing it?
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Fri 21 Jun, 2019 7:36 am

In my car the fan fuses are different
Fuse 7 = Back-up lamp, heater water valves, coolant pump, engine fan (i.e. electromagnetic fan), washer heater system, climate controller unit. = 8A(white)
Fuse D = Auxiliary Fan = 16A(red)

Here's a wiring diagram I redrew (your car may vary) -
WIRING DIAGRAM - Fan & Temperature Control.pdf
That shows for S25/4 3-pin Temp Switch that
when the 100deg contact closes Y2 Electromagnetic Clutch (Engine Fan) is engaged (using power from Fuse 7), and
when the 110deg contact closes K9 Aux Fan Relay is energized, thereby also switching on M4 Auxiliary Fan at full speed (using power from Fuse D).

Additionally, S32 A.C. Pressure Switch may come into play - if it closes, it engages K8 Double Contact Relay which then switches on both Y2 Electromagnetic Clutch Fan and M4 Auxiliary Fan (via a resistor R15 to limit the speed).

Simples!
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~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Fri 21 Jun, 2019 4:09 pm

Thanks Christo, you've been a great help, as always. It seems I've been very lucky by having no electromagnetic fan yet my Aux fan fuse is remaining intact. I'll see if I can get a 3-pin switch from the dealer and report back.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Sat 22 Jun, 2019 2:23 am

I bought a non-agent aftermarket 3-pin switch, it immediately pops fuse No. 7. One of the pins on the 2-pin side shorts directly to earth. It's probably best to buy electrical parts from the agents.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Mon 01 Jul, 2019 11:53 pm

I bought a 006 545 4224 switch from the agents. Strangely, when fitted, the temperature gauge no longer works. If I refit my switch (006 545 9124), the temperature gauge works (it seems the single pin on the switch has something to do with the temp gauge as the gauge stops working when this is disconnected). This seems strange as the gauge gets its signal from the single-pin switch on the thermostat housing (behind the vacuum and K-Jetronic sensors).

By now the brittle plastic connectors have started to crumble. Are they and the pins still available so that one can re-wire the harness?
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Tue 02 Jul, 2019 11:18 am

You didn't say your original 3-pin switch is Part Number 006 545 91 24....
it is quite a different animal from the switch 006 545 42 24
It is one switch and a temp-dependant resistor, not two switches:
as per these diagrams
PN_006_545_91_24.png
PN_006_545_42_24.png
therefore your system is quite different from earlier models like mine, and using the diagram for the 006 545 91 24 switch you could test it; if necessary must replace with same part number.
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~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Tue 02 Jul, 2019 4:36 pm

Christo C wrote:
Tue 02 Jul, 2019 11:18 am
You didn't say your original 3-pin switch is Part Number 006 545 91 24....
it is quite a different animal from the switch 006 545 42 24
Thank you Christo! I don't know where you get all your info from. :salute: I had no idea which switch was fitted until I took it out, actually until I compared the stamping with the replacement. I'm hoping the dealer will do a swop, especially now that I have supporting evidence that theirs is wrong. Strangely mine is the model with A/C, yet it has the non-A/C switch. Why would the 4224 prevent my temp gauge from working, after all, the single pin on the switch activates the AUX fan, while the dual-pin activates the electromagnetic fan, or am I wrong? Now I see the biggest difference is the colour, which I noticed but didn't pay much attention to.

Unfortunately the constant removal and replacement of connectors has resulted in them breaking (brittle due to heat over the years). Hopefully the agents still have them.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Tue 02 Jul, 2019 6:32 pm

The pins on those switches are 4mm, so standard 4mm “Banana” sockets can be utilised ....
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Tue 02 Jul, 2019 6:45 pm

Christo C wrote:
Tue 02 Jul, 2019 6:32 pm
The pins on those switches are 4mm, so standard 4mm “Banana” sockets can be utilised ....
The steel sockets are still okay, the plastic housings have crumbled. Can one still get them?
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Thu 04 Jul, 2019 9:13 pm

Might be hard to source those exact connectors now, so you may have to improvise.

Re-reading all above, and also discovering a wiring diagram which I think is closer to your situation, I think you can ignore what I said about the 3-pin device - seems yours has a switch for the electromagnetic clutch fan, and also has the thermistor for the Temp Gauge.

The Aux fan switching arrangement seems to be controlled by the Aircon Pressure switch and the Climate Control unit.

I’ll try to upload the circuit I found when I get a chance ... it’s not greatly clear unfortunately.

Any chance to tell me your VIN?
~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Thu 04 Jul, 2019 9:50 pm

Christo C wrote:
Thu 04 Jul, 2019 9:13 pm
I think you can ignore what I said about the 3-pin device - seems yours has a switch for the electromagnetic clutch fan, and also has the thermistor for the Temp Gauge.

The Aux fan switching arrangement seems to be controlled by the Aircon Pressure switch and the Climate Control unit.

I’ll try to upload the circuit I found when I get a chance ... it’s not greatly clear unfortunately.

Any chance to tell me your VIN?
My thermostat housing has three, actually four, switches:
  • Single-pin at the rear, which I assumed was for the temp gauge, yet the temp gauge does not deflect when the feed wire is connected to earth;
  • Dual-pin in front of that, closer to the radiator (fuel injection sensor?);
  • Vacuum switch next to that;
  • Single-pin + dual-pin 006 545 9124 switch in front (dual-pin for the electromagetic clutch, single-pin for the Level 2 AUX fan working through the relay (I assume). My A/C is currently without gas, the air pressure switch is thus not working - I have a leak, not sure where, hopefully not from the evaporator. The A/C needs to be converted from R12 to R134a.
VIN ADB1240236B777429
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Christo C » Fri 05 Jul, 2019 7:43 am

OK I found this in a parts diagram:

A 006 545 91 24 SWITCH,AUTOMATIC 98 WATER TEMPERATURE GAUGE & FAN COUPLING 100 GRAD

I think you will find that if you pull off just the single wire the Temp Gauge will stop working - Yes or No?

VIN starts with a W = WDB1240236B777429
Model 230E A A/C
Engine 102982 62 240747
Transmission 722408 202532
Order Number 0 2 675 18004
Order Location REPUBLIC OF SOUTH AFRICA
Interior LEATHER - BEIGE (265)
Paint 1 PEARL BLUE METALLIC (348U)
Delivery Date 1992-10-15
Approx. Build Date 1992-05

I think this is likely to be your wiring diagram:
WIRING DIAGRAM - Air con auto temp control 124_023 1987 on.pdf
There, S25/1 is shown as single switch.
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~Christo
1986 230E W124.023 M102.982 Thistle Green Saloon "Janis" 300,000+Km
Beaconsfield, SYDNEY

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Fri 05 Jul, 2019 6:03 pm

Thank you, Christo! :thumbup: I'll check the single connector over the weekend. The agents have ordered the correct part, it should be here on Monday.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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Re: W124 230E Thermostat Housing Sensors - How to Test?

Post by Ralf_CT » Wed 10 Jul, 2019 10:08 pm

Christo, it seems my car's wiring is different to yours:

The single pin on 006 545 9124 operates the temp gauge, the dual-pin the AUX fan on high speed. My electromagnetic fan is operated by the small blue two-pin switch behind 006 545 9124. That seems to be faulty in my case.
1992 W124 230E Auto, M102.982, 214,375 km, MBSA-built - CURRENT.
1985 W123 280E Auto, M110.988, 110,265km, MBSA-built - SOLD.
1985 W123 230E Manual, M102.982, 219,320 km, MBSA-built - SOLD! :(

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