220E - Heater Woes

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220E - Heater Woes

Post by RavzSa » Mon 11 Mar, 2019 1:25 am

Hi All,

First time poster! Very informative forum

I now have this car for about 10years and from day one the heater has never worked.

I've always suspected that it was the electrics to the duo-valve that was the cause, so today I removed the little valves / pistons from the duo-valve to allow continuous hot water through.

Now even after doing this, there's no heat. I checked the inlet hose to the heater matrix and found it hot, but the pipes on the outlet side were not even warm.

So I now removed the hoses and flushed out the heater matrix using a garden hose. I observed some coolant flow out followed by clean water. There was a nice flow of coolant and water, therefore I assume no blockage?

I thereafter connected the inlet hose to the heater matrix and left the outlet hose at the duo-valve end unconnected and ran the car. Whilst idling no coolant passed through the duo-valve, not even a trickle. If I kept a constant idle around 2000rpm there was a very slight trickle of coolant.

Surely this is not how it supposed to be?

I have also checked the auxiliary pump adjacent to the duo-valve which does work when the heat dial is set to max.

Any help is greatly appreciated!
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Re: 220E - Heater Woes

Post by CraigB » Mon 11 Mar, 2019 9:22 pm

I'm interested on responses - sounds odd, but you seem to have it narrowed down
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Re: 220E - Heater Woes

Post by Christo C » Tue 12 Mar, 2019 9:50 am

On my 230E the Duo Valves are energized when the heater is OFF - i.e. the 2 outer pins of the Duo Valve connector are grounded (-ve) by the Heater Controller unit, and the centre pin is always +12. That ensures that "fail" condition of these valves (should they go 'open circuit') is Heater ON, which I imagine is important is very cold climates, but seems entirely inappropriate in most parts of Australia :Doh: .

Therefore, as you seem to have found that fluid flows through the heater OK, and the small Circulating Pump is functioning, if you unplug the Duo Valve electrical connection your heater should function... does it?

Another test is to turn the Ignition Switch ON (next detent past accessory) but not start the engine, and plug/unplug the Duo Valve 3-pin connector - do you hear Duo Valves clicking when you do that?

I am surmising perhaps the Heater Controller unit is possibly not turning the Duo Valves off (i.e. by disabling their Ground / -ve supply). Maybe you can check that with a multimeter or globe.

(The Heater Controller senses temperatures at both the LH Heat Exchanger and RH Heat Exchanger, as well as the Inside Temp sensor, usually located in the Cabin Roof Light assembly).
~Christo
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Re: 220E - Heater Woes

Post by RavzSa » Thu 14 Mar, 2019 5:36 am

So I have checked the duo-valve and it does click when connected. I even stripped the duo-valve and confirmed that the solenoids activate when the dials are adjusted - albeit they just move up or down and do not pulse as suggested in other posts that I have read.

I have also used the car with the duo-valve unplugged for a few months and not a single day did I get heat.

So now I wanted to remove the electrical side from the problem and go down to basics, so currently the inner valve is removed from the unit allowing continuous flow of coolant, which again is not providing heat.

So the other evening I let the car idle for about 10 minutes and tried to "burp" the system in case of airlock. This achieved nothing.

I then removed the hose to the inlet of the heater core while the car was running (just for a few seconds as i did not want to lose coolant) and confirmed that coolant is being pumped to the heater matrix. The pressure although not as high as what I got from the garden hose I used to flush the heater core.

So know I assume (might be on to absolutely nothing here) that the heater matrix is semi blocked and the pressure produced by the engine not being as high as the garden hose, doesn't have enough pressure to push past the blockage.

So this weekend I plan to reverse flush the core with citric acid and see if that actually does anything.
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Re: 220E - Heater Woes

Post by John Green » Thu 14 Mar, 2019 9:51 am

Can't remember what the flaps are like inside a W124 heater box, but you might be totally on the wrong path. Most cars have a flap that directs air over either the heater core or the a/c evaporator. If it is blocking air flow to the heater core, then you will have no heat.
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Re: 220E - Heater Woes

Post by Christo C » Thu 14 Mar, 2019 3:59 pm

I’m wondering if there are flaps ? - on my W124 it’s possible to have Cold air from the centre outlets and Hot air everywhere else - a useful, if not interesting, feature - by having the top Aircon button down and the two Temp wheels turned to a hot setting. Result = cold air in your face and warm feet! 😎

In my car there is no evidence of any flaps controlled by the Temp Regulator that I can find...

Regardless of the above Aircon switches, when the Temp wheels are set at their Hottest setting, the Duo Valves should be Open (i.e. no power applied), and the Circulation Pump should be running.
~Christo
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Re: 220E - Heater Woes

Post by RavzSa » Fri 15 Mar, 2019 5:36 am

John Green wrote:
Thu 14 Mar, 2019 9:51 am
Can't remember what the flaps are like inside a W124 heater box, but you might be totally on the wrong path. Most cars have a flap that directs air over either the heater core or the a/c evaporator. If it is blocking air flow to the heater core, then you will have no heat.
But surely even if there are flaps, I should still have coolant flow from the outlet of the heater matrix...
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Re: 220E - Heater Woes

Post by RavzSa » Fri 15 Mar, 2019 5:41 am

Christo C wrote:
Thu 14 Mar, 2019 3:59 pm

Regardless of the above Aircon switches, when the Temp wheels are set at their Hottest setting, the Duo Valves should be Open (i.e. no power applied), and the Circulation Pump should be running.
Circulation pump is running and valves are open but no coolant circulation

So that dash is out, if I this acid flush doesnt work, I have no choice but to pull the HVAC box out of the car and check the heater matrix. Really trying to avoid this....

Any tips for the acid flush?
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Re: 220E - Heater Woes

Post by CraigB » Fri 15 Mar, 2019 10:03 am

Good to bring up the issue of flaps in a thread like this, but you are talking about actual flow of coolant that you are looking at. Sorry can't help on the acid. I was just going to say, depending on the construction of the heater core, if you have put all that labour into pulling it out (if you need to) I took one from a mates suzuki i was fixing to one of the few 'old school' radiator places in Adelaide and they repaired it for not crazy money - new expensive i would think and never quite know what you are buying used. Just a suggestion to think about.
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Re: 220E - Heater Woes

Post by RavzSa » Sun 17 Mar, 2019 2:09 am

So update;

Today I did the reverse citric acid flush on the heater matrix and to my surprise not a lot of dirt came out. A few flakes of what looked like rust and some brown muck came out after about 2 litres of flushing and thereafter the water came out relatively clean.

Hooked the inlet hose back to the engine, gave it a few steps on the throttle and now for the first time ever coolant comes spraying out of the duo valve outlet! hooray! attach all hoses back to the duo-valve and guess what?! no heat....

So I take the hose out from the duo-valve to the engine block to check for blockages, and to my surprise I find a rubber stopper lodged deep into the hose! Remove the stopper, attach the hose and... there's heat!

I assume the PO had issues with the duo-valve or the heater matrix and had the pipe blocked. I checked inside the cabin for dampness and found nothing so far... so I'm hoping the duo-valve was the reason the pipe was blocked.

But now I have another issue, I only get heat when the temperatures dials are set to max. Everything between max heat and the lowest temp setting does absolutely nothing. I even checked the duo-valve if it pulses and nothing.

What could be the issue here?
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Re: 220E - Heater Woes

Post by Christo C » Sun 17 Mar, 2019 9:07 am

So I take the hose out from the duo-valve to the engine block to check for blockages, and to my surprise I find a rubber stopper lodged deep into the hose! Remove the stopper, attach the hose and... there's heat!
Good grief Batman! How did we all miss that ! :banghead:
But now I have another issue, I only get heat when the temperatures dials are set to max. Everything between max heat and the lowest temp setting does absolutely nothing. I even checked the duo-valve if it pulses and nothing.
I found that happened intermittently too in my car, but only on one dial - after dismantling the dial unit I found a dry solder joint on one leg of the dial's potentiometer.

heater_dial_sml.png

Re-soldered and it works fine. Also a little spray of good quality Electronic Contact Cleaner into both the potentiometers helps.

Not saying that is your problem, but it could be, or worn out Potentiometers, or it could possibly be a bad Temperature Sensor somewhere ..... or ...
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Re: 220E - Heater Woes

Post by RavzSa » Mon 18 Mar, 2019 3:17 am

Christo C wrote:
Sun 17 Mar, 2019 9:07 am

Good grief Batman! How did we all miss that ! :banghead:

I did check this pipe previously, but to my stupidity only checked on the inlet side :Doh:

I found that happened intermittently too in my car, but only on one dial - after dismantling the dial unit I found a dry solder joint on one leg of the dial's potentiometer.


heater_dial_sml.png
Might sound like a stupid question, but how do I get the circuit out of the plastic housing. There is 2 screws at the corners holding it in place which I have removed, but still cant seem to get it off. Its being held back in the center where the pins are. I notice in your image there are clips that hold the connecting pins to the plastic body, how do you free those?

Would you also know how to test the potentiometer with a multi-meter?
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Re: 220E - Heater Woes

Post by Christo C » Mon 18 Mar, 2019 7:18 am

I notice in your image there are clips that hold the connecting pins to the plastic body, how do you free those?
from memory I just wriggled it off, probably aided with a small screw driver to gently push those clips in a bit....

I didn't think to measure the actual overall resistance of the Potentiometers; in a nutshell, with the multimeter set to Ohms (Ω) you should measure some set overall value across the two outer pins of the Potentiometer - then, measuring between the centre pin and one of the end pins, you should get a variable reading between zero and the set overall value, depending on the rotation of the device.

This diagram may help
Potentiometer.png
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~Christo
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Re: 220E - Heater Woes

Post by RavzSa » Mon 18 Mar, 2019 8:52 am

So I still cant get the board out! I even tried to pry it out with a screwdriver and still nothing.

I see mines is a bit different to the one in the photo...

Image

Image

So I think my pots are dead...

Image

I took a multi-meter, set it to OHM's and tested resistance and got the following;

Contact 1 and 3 = approx 3.9
Contact 1 and 2 at max = 3.8 -3.9
Contact 1 and 2 at min = 3.4 -3.5

Now measuring between contact 1 and 2 and anywhere between min and max gave me absolutely no reading. So I assume the contact along the track is non existent or dirty.

Going to get some contact cleaner and hopefully that sorts it out.

Now I did test the pot while still soldered to the circuit board, would this have affected the readings on 1 and 2? I assume not as I did get readings when set to min and max..... :think:

If I need to replace the pots can it be replaced with something similar? I believe I need to match the resistance rating of these pots, but I have no idea what they are!
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Re: 220E - Heater Woes

Post by Christo C » Mon 18 Mar, 2019 4:47 pm

Ah yes although the plastic cover looks same that board is different! Your circuit board has many active components; mine hardly any, indeed just a few resistors, the potentiometers and somr globes.
On mine there were 2 small screws on the circuit board surface to be removed first, then some simple retaining clips to spring open.

Sorry I don’t know the resistance of the potentiometers or what scale your meter is on for those readings... but at one extremity the potentiometer should read zero (0) ohms between pins 1 & 2, same as when the meter probes are simply touched together.

Hopefully Contact Cleaner helps...
~Christo
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Re: 220E - Heater Woes

Post by Bartman4800 » Mon 18 Mar, 2019 5:13 pm

Looking at that picture, I think your pin 2 on that potmeter is the common

You should be measuring either between 1 and 2 or between 2 and 3

The resistance between 1 and 3 is fixed (as you measured).

A good squirt of contact cleaner with some wild movement of the pot dial does wonders...


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Re: 220E - Heater Woes

Post by RavzSa » Tue 19 Mar, 2019 8:49 am

Thanks for all the feedback and advise guys!

So I got some contact cleaner today and cleaned up the pots.

After cleaning I now get totally different readings to what I measured yesterday. Haven't had a chance to try it out on the car yet, but these are the readings I measured today. These readings were taken at intervals according to the temperature dial;

Total resistance measured between 1 and 3 - 47,8k
Min (16) - 47.3k
18 - 51.9k
22 - 53.0k
26 - 52k
max - 46.3k

Note - pots still connected to the circuit board.

I tested both pots and had similar readings between the two but they just don't seem right :think: - the values seem too close together :think:

Will test on the car tomorrow and see how it responds.

How should a properly working duo-valve function at the in between 18 - 26? Would the solenoids continuously "pulse" or hypothetically "pulse" every 30 seconds or so depending on the temperature setting?
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Re: 220E - Heater Woes

Post by Christo C » Tue 19 Mar, 2019 12:13 pm

Total resistance measured between 1 and 3 - 47,8k
Assuming it is Linear Potentiometer, if you set it at about halfway rotation, you should get approx 24k ohms between Pins 1 & 2 or Pins 2 & 3. In any case the resistances between Pins 1 & 2 and Pins 2 & 3 should ADD up to the total between Pins 1 & 3... it shouldn’t make much difference that the Potentiometer is connected in circuit...

As I understand it, the function of the Duo Valves depends on those Control settings as well as the various sensed Temperatures as determined by the Heater Controller.
~Christo
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Re: 220E - Heater Woes

Post by RavzSa » Wed 20 Mar, 2019 5:33 am

So connected the CCU and its still pretty much the same

Is there a way to test the sensors in the HVAC box and the sensor connected the little fan behind the glove box or is there some other component that I should be looking at next instead of the sensors?

Image
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Re: 220E - Heater Woes

Post by Christo C » Thu 21 Mar, 2019 6:39 pm

The temperature sensors are simply Thermistors = Temperature dependant resistors.
The one in my Cabin Light in my car (with tube down to small fan behind glovebox) measures around 4,200 Ohms (4.2k Ohm) @ about 28DegC. I think the other sensors are the same devices.
Thermistors are generally very reliable but mostly fail Open Circuit, therefore will read many MegOhms, or rarely fail dead short therefore will read just a few Ohms.

Beyond that your problem is probably beyond my pay grade! Certainly my early W124 is less complicated than yours judging by your pictures.
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Re: 220E - Heater Woes

Post by RavzSa » Fri 22 Mar, 2019 2:25 am

Christo C wrote:
Thu 21 Mar, 2019 6:39 pm
The temperature sensors are simply Thermistors = Temperature dependant resistors.
The one in my Cabin Light in my car (with tube down to small fan behind glovebox) measures around 4,200 Ohms (4.2k Ohm) @ about 28DegC. I think the other sensors are the same devices.
Thermistors are generally very reliable but mostly fail Open Circuit, therefore will read many MegOhms, or rarely fail dead short therefore will read just a few Ohms.

Beyond that your problem is probably beyond my pay grade! Certainly my early W124 is less complicated than yours judging by your pictures.
Thanks for the explanation!

I tested all of the sensors and measured the resistance against the values given in the workshop manual and they all seem to be within tolerance.

What I found now, is that when the cabin sensor (the sensor mounted in the interior light fixture) is disconnected, the duo-valve and circulation pump kick in through all the heat ranges. I assume this is because the CCU now assumes that the cabin is freezing cold.

With the cabin sensor testing out fine, not sure why its not switching the duo-valve on when connected :think:
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Re: 220E - Heater Woes

Post by Ivanerrol » Fri 22 Mar, 2019 11:36 pm

I am going to assume.

You found a blockage in the thermal coolant circuit.
There is probably another somewhere.
The heater condenser is similar to the radiator - lots of little capillaries to allow the heat to be exchanged.

Have you checked the hose from the heater circuit back into the engine block at the back of the engine?

With the electrical connectors off the duo valve you should get full heat through the system.

With the heater controls set at around 22 degrees. On a cold day should able to hear the duo valve clicking in and out.

Do you have a multi-meter to check the differing voltage at the duo valve depending on the position of the heat level required at the console controller?
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Re: 220E - Heater Woes

Post by RavzSa » Sat 23 Mar, 2019 1:14 am

Ivanerrol wrote:
Fri 22 Mar, 2019 11:36 pm
I am going to assume.

You found a blockage in the thermal coolant circuit.
There is probably another somewhere.
The heater condenser is similar to the radiator - lots of little capillaries to allow the heat to be exchanged.

Have you checked the hose from the heater circuit back into the engine block at the back of the engine?

With the electrical connectors off the duo valve you should get full heat through the system.

With the heater controls set at around 22 degrees. On a cold day should able to hear the duo valve clicking in and out.

Do you have a multi-meter to check the differing voltage at the duo valve depending on the position of the heat level required at the console controller?
So I have the heater matrix unblocked and working now.

The challenge I sit with now is that I can only get the duo-valve to switch on when the temperature dials are set to max heat or when I remove the cabin sensor.

Although my A/C does not work, I would assume on a day where the ambient temperature is approx 25 degrees, when the heater is set to 26 I should get some heat?

Would it be possible to remove the cabin sensor and connect a 16k ohm resistor to trick the CCU to believe its around 15 degrees?
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Re: 220E - Heater Woes

Post by Christo C » Sat 23 Mar, 2019 6:42 pm

Although my A/C does not work, I would assume on a day where the ambient temperature is approx 25 degrees, when the heater is set to 26 I should get some heat?
Pretty high expectations I think; you need a greater difference between actual and desired temperature; mine certainly is nothing as precise, but the heater works on cold days.... @25deg do you really want to be warmer?

In electronics, Thermistors are the one of the crudest way to measure temperature.
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Re: 220E - Heater Woes

Post by RavzSa » Sun 24 Mar, 2019 8:23 am

Christo C wrote:
Sat 23 Mar, 2019 6:42 pm

Pretty high expectations I think; you need a greater difference between actual and desired temperature; mine certainly is nothing as precise, but the heater works on cold days.... @25deg do you really want to be warmer?
Haha, no I wouldn't want to be any warmer, but since having this car I've never had the heater or A/C work so not sure how the climate control actually responds.

So today I tried out a 12k resistor and it worked. The CCU thought it was around 21 degrees and the car was able to supply heat anywhere above 24 or so on the dial. So I'm assuming its been just too warm here since testing so will have to wait for a cold day to test it out properly!
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