W124 climate - auto works for cold not for hot

[larsko]

Hi I'm having issues with the climate control on my1990 w124 300e. It's the push button type climate control. And first: I've replaced the blower motor and regulator, serviced the mono valve, replaced the water temp sensor on the engine block. (The a/c is out of gas and not working).

The fan works as it should on high and low setting.

On auto if I set the temperature setting to min the fan spins up to max and blows cold air. Increasing the temperature, the fan slows down as it should. Fan blows at min around 22C. Seems to work except for when I set the temperature to max, the fan blows hot air maybe like 2 of 4 on a manual system. If I push the defrost button it speeds up somewhat but nowhere near full speed.

Where do I look? Does the climate relay behind the battery have anything to do with this? Could it be the push button unit itself? The internal temp sensor? I'm at loss - would appreciate some tips (hot air is much more important than cold air in Norway anyway )

[Diseasel300]

The Klima relay controls the A/C clutch. It won't be your issue here, especially since the refrigerant has leaked out.

I'd suspect the issue lies in the pushbutton unit itself or the "porcupine" blower motor controller, although you said you just replaced that.

My SDL (which has a similar HVAC system) had goofy fan controls in "Auto" as well, it only ever seemed to blow full or blow low and there was no real rhyme or reason to what it was doing. High fan and Low fan would produce the proper results, but "Auto" was all over the place.

I got brave and rebuilt my pushbutton unit in a desperate attempt at getting some A/C. One of the things I did was replace all of the electrolytic capacitors on the circuit board. In addition to getting my compressor working, it also seems to have restored proper operation of the "Auto" fan function. Instead of just abruptly changing between high and low randomly, it seems to gradually change speed and hold at various levels depending on where the temperature is set and what the temperature of the car is. Very clever...

[larsko]

Clever! A bit beyond my skills. Perhaps look for a complete new unit... thanks!

[larsko]

Update: cleaned the temp sensor in the roof panel today. Lots of dust and dirt in there. And it is better. Still no max speed on max heat or defrost but more speed than it used to have... weird