HPF

My W203 2005 model cooling/heating system has worked fine for almost 8 years now except 1-2 years ago when the A/C wouldn't blow cold air anymore. A refill fixed that problem.

This evening the heating system worked fine when I drove to a friend of mine.

3-4 hours later I started the car to drive home and the Thermatic panel, that used to light up, stayed black. The Thermatic panel doesn't respond to any of the buttons except the A/C OFF button. If I press that button the A/C OFF red LED lamp will light and the Thermatic panel will light up also...but that's all.

When I press defrost button I can hear something move inside the dashboard, but no fan start and no LED light turn on.

The Thermatic panel is same as the ACoff-REST (third from top) here
https://mbworld.org/forums/attachment...trol_units.jpg

Suggestions on how this can be fixed is highly appreciated.

Glyn M Ruck

Before you can diagnose anything make sure that your refrigerant pressure is correct. Why did it require a refill? Did they find a leak? Did they fix it? If pressure is too low it will shut down the system to protect the compressor.

Then check the pressure/temperature switch/sensor in the base of the condenser at the base of the radiator.

If all is good then you likely need a new controller.

Glyn M Ruck

Also check fuses. 30, 41 & 51

HPF

AC stopped working. Don't remember if the fan stopped working also or if it just stopped blowing cold air.

Workshop said it was timeconsuming to find a small leakage and they said sometimes refill was required even if there was no leakage. To save money and time they just refilled and also added something that would leave color or something to spot where the leakage is (if any).

Is there a way I can check the refrigant pressure myself?

Glyn M Ruck

I do not advise it. Take it to an HVAC specialist. I do not recommend working on a pressurised AC system without the correct equipment. You don't have to go to a dealer.

HPF

OK, thanks for info. The B12/2 on the picture, if damaged can that cause the problems? At my friends house yesterday it was limited space to turn so I drove the front of the car into a snowdrift.

Glyn M Ruck

Yes. That is the pressure/temp sensor. If it reads incorrectly e.g. no pressure ~ it will shut down the system.

HPF

Also noticed today that radiator fan run at full speed even after coldstart and minus 4°C outside. Talked with workshop that suspected the Thermatic controller unit need to be replaced. New one cost €550, I can get a used one for €150.

Does the Thermatic controller also controll the radiator fan speed? The engine coolant temperatur displays correctly though so either engine coolant temp is not governing the radiator fan directly or the radiator fan doubles as HVAC radiator fan also and run at full speed for some reason, ie no HVAC temp input.

Not even the heating wires in rear window work....can defect HVAC pressure/temp sensor cause that? I mean it's logic it shuts down the HVAC, but the heating wires for rear window also?

Guess I want the Thermatic controller unit to be broken so I can buy a used one and change myself

HPF

For some reason it started to work again after being completely dead for 4 days. It coincides with a temperature increase from below freezing point to above.

Glyn M Ruck

The radiator fan has it's own controller on a fly lead from the fan. It is speed controlled by the ECU. The radiator fan should run immediately your turn on the AC. Speed will vary on condensor temp & engine temp.

Seems something is messing with the pressure temp sensor. I hope you have no water in the refrigerant circuit that is freezing.