PeachParts Mercedes-Benz Forum - View Single Post - 1987 300TDT (W124) Climate Control Problems

swogee · #11 12-15-2005, 07:33 PM

I finally got around to checking out the climate control on my 1987 300TDT. I unplugged the aux. heater pump from the harness, and the ACC seemed to work normally. The air seems to properly come out of the footwell vents when the ACC is in heat mode. I measured the voltage across the pump wire harness jack with pump unplugged when the ACC was operating in heat mode and the voltage was 13V. As soon as I plugged the pump in, the voltage dropped to zero and the ACC started acting funny.

I ordered a new Bosch aux. pump (they aren't cheap, but it is cheaper than a ACC control unit) and installed it. The ACC now seems to work properly. The old pump must have been frozen or something. There was also corrosion on the outside of the pump.

jcyuhn, thanks for the great advice. I was also reading the W124 owner's bible and it lists "heater is always at maximum heat when in heat mode" as a symptom of a bad aux. heater pump. My ACC had that symptom as well.

Thanks again for the help troubleshooting.

-Steve