w201 Tempmatic Climate Control Problem - PeachParts Mercedes-Benz Forum

kiato4 · #1 08-07-2003, 12:49 AM

Hey all:
I need a help with my tempmatic climate control. It is a 1987 model so there is no EC button. The problem is such that I cannot use my newly reconditioned (new condensor) and converted to R134a AC because the defroster will continuously blow heat. When I push the dehumidfy button (the top of the three vertically lined up buttons on the right of the climate control panel), I feel the AC compressor engage and the middle vents blow cold air, but the defroster will never stop blowing hot air. When I push the AC button (the middle button in the same location), the AC compressor does not even turn on. I think that I have two problems, 1. There is a vacuum problem (heater valve?) that will not close the defroster 2. The AC button or inside car temperature sensor are broken and do not sense that the AC must turn on. Any help would be greatly appreciated, I cannot drive in this weather with heat.

mbdoc · #2 08-07-2003, 08:10 AM

Vacuum supply to the switch-over valve assembly is the KEY to correct operation on the W201 chassis A/C system. Just to the right of the glove box inner liner is the switch-over valve(s), you need to check vacuum supply there.

Mercedes Maniac · #3 08-07-2003, 10:13 AM

Hi,
Also having problems with '87 W201 A/C. Fortunately I have a second vehicle that I can use in the heat. I am looking at a Tempmatic control P/N 201-830-0785, a rebuilt by CCI Uptime, I have zero compressor engagement, auxilary pump was previously disconected. I will be doing more trouble shooting over the next two weeks. For more info on system, download from this site info on control P/N. http://www.programainc.com/?go=technical_support&v=3 Keep us posted, Thanx.

kiato4 · #4 08-25-2003, 08:45 PM

I have an update on this problem. My mechanic opened up the glove box liner and checked out the switch over valve. He said all the valves are fine. He showed me that if he disconnected one vacuum line and applied vacuum to it manually with his mouth, the flaps would shut and air conditioned instead of heated air would get to the defroster. He is still working on it, but I just want to clarify what this means. Does this mean that there is a vacuum leak somewhere (if so, where are the common problem areas) or is there some sort of electrical connection problem. I performed another check, in that I checked to see the voltage at the feedback potentiometer and no matter what setting I put the temperature wheel at, the voltage did not change across that part.

Mercedes Maniac, thanks for the link. According to that sheet, I have either an electrical connection problem or a vacuum leak.

moneypit · #5 08-26-2003, 10:01 PM

i had a similar problem on my 190e. it was caused by a crack in the vac hose to the monovalve. when i fixed it the pods for the defrost flap and fresh air flap blew out. i changed them all including the monovalve and my ac works great. not sure this is your problem but just wanted to share my experience with you. good luck!