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W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Thu 16 Jul, 2015 12:29 pm
by chopper0813
Vacuum Diagram.png
Hi Folks,
About six months ago I purchased a 1997 W202 C200, the car was located in Sydney, I live in Cairns and so accepted remote engineering inspections. On receiving the vehicle, although the a/c system produced cold air, it only worked through the centre vents.
A closer inspection revealed that the outside temperature sensor had worn off by contact with the road and the coolant supply to the duo-valve had been blanked off.
The outside temperature sensor was replaced, the duo-valve serviced as both valves were stuck open. The air conditioner then seemed to function correctly with good temperature control.
Despite all efforts, there is a leak of defrost air to the defrost vents continuously. Using an endoscope through the defrost vents, the defrost flaps can be seen stuck slightly open and do not move with changes in the airflow switch. I have changed the climate controller but the results are the same.
Using a long grabbing tool through the top vents, the defrost flaps can be moved open and closed.
I believe the next step is to locate the vacuum valve block and test the defrost flap vacuum and electrical connections.
I just can't find the location of the vacuum valve block, I see on other forums that the LHD vehicles have it mounted on the blower case or behind the glove box.
Can somebody help me with its location?

Following all the diagnostic work above (Now 7th September) further examination of the EPC by VIN tells me the item I am searching for is a VALVE.
Item 5 on the EPC part No. A2028000278 or A2028000378. Confusingly, the EPC shows a LHD vehicle A/C system.
The EPC shows the VALVE positioned on the front face of the heater box, following a serious search I am still unable to physically locate it.
The page from the EPC is attached at the beginning of this post, hopefully some knowledgeable person will be able to help me solve this problem.

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 16 Jul, 2017 12:21 am
by Tenorite_320
Hi Chopper,

I have been researching a similar problem on my W202 280 Sport with virtually no air flow to the front windscreen with heater controls in the demist position - did you find a solution to this problem?

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 16 Jul, 2017 3:03 am
by Tony From West Oz
WHOA. Do not buy anything or muck around at this stage. The issue is most likely to be a simple mechanical disconnect.
Step 1. Remove the fascia from the HVAC controls, radio, etc.
Step 2. Remove radio. Feel up behind RHS of heater controls via radio opening. Are both linkages attached to the air box? If one or both of these is not connected, the air distribution control will not work correctly. If this is the case, continue:
Step 3. Remove HVAC controls
With HVAC Controls removed, align the air distribution knob so that the linkage sockets are aligned with the orientation of the air box linkage plugs.
Replace HVAC Controls, using a hand up the radio opening to help the linkages mate correctly. It is fiddly, but it helps to get it back together.

Step 4. Before replacing the radio and screwing everything up again, test the airflow control to ensure that it sends air where directed.
Once all working correctly:
Step 5. Reinstall radio and replace all screws
Step 6. Replace the fascia.

Drive and enjoy the HVAC, as it should work.

How do I know the above?
I needed to replace the globes in the HVAC controls and managed to not mate the linkages. Live and learn!

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 16 Jul, 2017 11:08 am
by chopper0813
Hi Folks,
My problem in fixing the defrost air leak was that I wrongly utilised the vacuum control information for the automatic climate control unit, most of which applies to LHD vehicles. Some time later I understood that the air control flaps (with the exception of fresh air) are moved manually. As Tony says, unless the operating spigots are connected correctly to the air box levers, nothing happens.
To fix my defrost air problem I needed to replace the RH flap operating lever as it had broken off.
Below is the post detailing my work in fixing the problem

viewtopic.php?f=26&t=21759

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 16 Jul, 2017 1:39 pm
by Ivanerrol
For other air circulation problems.
This is the vacuum distributor in the earlier W202's
AC compressor rings.JPG
Note the green line - it's broken off. The circulation wont work properly

Here's another controller. It's underneath the glove box in front of the fan
AC controller.jpg

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 23 Jul, 2017 1:47 pm
by Tenorite_320
Appreciate the comprehensive replies - with the radio and HVAC control unit removed this morning, I could manually operate the air distribution controls using a screw driver and the air flow was definitely alternating between the screen and the face/foot level vents. On that basis, it appeared the vacuum controls were operating correctly. A bit more sitting there looking at the problem and determined the control knob for air distribution in the HVAC control unit was upside down - rotated it 180 degrees and it works perfectly. Thanks again.

Re: W202 1997 C200 Air Conditioning System- Defrost Flaps

Posted: Sun 23 Jul, 2017 2:50 pm
by Tony From West Oz
Happy to help you.
I was having problems like yours after replacing light globes in the HVAC control panel. Then the demist stopped working, it was easy to identify the cause.