Looking forANY ideas. I have a 1991 300E, 3.0 motor. The A/C has been converted to the new stuff. In the morning, the car blows nice and cold. Later in the day, as the motor gets hot and the weather warms up. the A/C does not blow cold. Compressor is a couple years old. Is there a thermo switch of some sort somewhere that could stop the compressor from engaging? The compressor does not seem to be engaging when the motor is hot. Thanks in advance for any suggestions.

 

On the newer models we have onboard diagnostics that you run to get the sensor values.Usually if you have a cold run hot not run it is a sensor reporting an out of range temp.If the evaporator temp sensor is faulty it will shut down the compressor to prevent freezing up the coil.You most likely have run into the scenario however with no way to check it you are going to need to get to a shop that works on mb and have them test the system.
AS long as it is working at least it should not be that much to track down the faulty sensor.
I hope

 

After checking electrical connections, i found that the compressor is turnig on. I pulled one of the wires off the black A/C hi low switch and the compressor went off. I replaced it and it went on. Then i moved up to the cylinder head where there is an "AC Cutoff Switch; On Cylinder Head; Blue Insulator with 2 Prong Connector; 130 Degree C" I removed one of the wires and then the front condensor fans fired up. Instantly the car was blowing cold again. Ire-installed the wire and the fans went off and started blowing warm again. I guess this means I need a newA/C cut off switch. I will replace for 17.00 and see if that works. In the mean timedoes anyone seem to think running the fans all the time for a couple days will cause any problems? thanks,

 

No problem at all.
good trouble shooting
www.autohausaz.com has the switch.
ohlord