190E AC Trouble
 

I have a 92 190E2.6 with 138,000mi. When sitting in traffic or parked and idling on hot days, the ac stops working until the car is back in motion and has cooled down. When this happens, the engine temp is just below 100C. I have bypassed the MAS module and also bypassed the climate control engine temperature by installing a fixed resistor into connector to simulate a cool motor. I have also recharged the system as it was a little low. Aux fans have been wired on low to increase airflow at idle. I have not bypassed the refrigerant pressure switch yet. Any ideas? My wife and kid are sweating in the afternoon shcool pickup line.

Rod

Is the compressor engaged when it is not cooling?

I do not know if it is or not. I am not in the car when it happens but it is temperature related. Driving down the road for hours and it will work fine, but stop in traffic or park while idleing and it will quit. Once the car is back up to speed and the engine temp drops then the AC begins to work again. I may just wire up a manual engage button to engage the compressor for my wife to push when it quits to see if the AC starts cooling.

I'm not sure about the 2.6, but the 2.3 has a single-wire temperature sensor that cuts out the A/C at what it percieves as too high a temperature. You could bypass this to keep your A/C functional. I had this sensor go bad on my old 2.3 and as a result the A/C would never engage.

I have bypassed the temperature sensor for the climate control by installing a fixed resistor in the plug(2 pole) to simulate an engine temp of less than 80C. The only thing I have not bypassed is the pressure sensor. I may do that tonight as it is getting too late to wire in an manual switch for the compressor clutch for testing.

Sorry I wasn't too clear. The sensor I speak of is a coolant sensor that is of the on/off variety. It's only function is to cut off the A/C when it sees a high coolant temp. I don't believe it has any other climate control or fan control function.

On my car it uses a temperature sensor mounted in the head close to the temp sensor for the CIS computer. The sensor goes back to the Tempmatic control unit in the dash and if the engine temp gets to 117C it will cycle the compressor at 50% and at engine temp of 120C it will disengage the compressor. I bypassed the pressure switch and will see what the wife says when she get home today.