I have a 1987 190E 2.3 8V. The AC cuts off after 5 mins or so. My mech has looked at it. The relay checked out. So did the freon and compressor. I have recently replaced the blower control assembly. What is causing it to cut cold air?

Possible causes->bad high pressure switch->temp sensor in the evaporator housing->control relay..

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Jeff L
1987 300e
1989 300e
1987 BMW 325

If the problem is the compressor shutting off I would look into your belt tentioner. The Klima relay (compressor control relay) uses a number of signals to decide whether to turn on the compressor. The first signal is the actual A/C on signal from the pushbutton controller. You can verify what this signal looks like by testing at the low pressure switch when the compressor works (some of the systems trigger with a groung some a voltage signal [its a diesel versus gas thing and I can never remember which is which]). The signal passes through the low pressure switch so its an easy place to test. Decide while its working which side comes from the pushbutton unit and which goes to the compressor controller (so you can test the signal when it shuts down).

The other inputs are temp (switch cuts it off at 110deg C) The final and most critical element is the comparison of compressor speed to engine speed; this is where the belt tentioner comes in. The purpose of this control is to shut-off the compressor when it locks up to prevent burning out the belt which also turns the water pump among other things. This is so sensitive that if you have a belt chatter it will set the control off and the comp will shut down until the next ignition cycle.

Of course the speed sensor and the engine speed signal are also critical but the are very seldom the problem. The only comp speed signal problems I have seen have been on rebuilt compressors where in construction they got the end of the compressor shaft too far from the sensor.

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Steve Brotherton
Owner 24 bay BSC
Bosch Master, ASE master L1
26 years MB technician

A BAD BELT TENSIONER (LOOSE BELT)WILL CUT OUT COMP.,A BAD COOLANT TEMP. SENSOR WILL SHUT YOU DOWN IF IT THINKS THINGS ARE TOO HOT!,IF YOUR FEEDBACK POTENTIOMETER IS OUT OF ADJUSTMENT YOU CAN LOOSE YOUR COOL....BUT YOU CAN OVERRIDE IT BY USING TOP RIGHT A/C BUTTON!!
M.F.

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M.F.

I have had weird ones like this.. And sometimes it is the potentiometer under the dash. I have seen more than one do this.

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Benzmac:
1981 280GE SWB
1987 16V
ASE CERTIFIED MASTER AUTO TECHNICIAN
SERVICE MANAGER FOR 14 BAY FACILITY
MERCEDES SPECIALIST 8 YRS
PARTNER IN MERCEDESSHOP.COM

This works for me. Push the top right button on 86 190E and compressor engages and cold air blows out. Very nice. Then it cuts out after about ten minutes. This is the only way to get cold air out of the system. Otherwise, the system blows hot air on all settings. Car has been retrofitted by dealer to R132 or what ever it is called and several parts and hoses have been replaced over the years. No good fix. Any idea what is going on? Thanks for your time.