1988 300SE Air Condicioner
 

Compressor does not engage. Recommended check high - low sensor (switch? ) could not locate. Where and what do I look for and how do I check? Anything else I may check. Switches on 5 panel seem to engage properly, air flow changes to correct ports. Heater works. Thanks Brian

Is the A/C fully charged? No freon, compressor does nto engange.

There are two pressure switches on the receiver drier behind the left headlight. One breaks the power to the compressor clutch when the pressure is too low, one sends power to the auxiliary fan circuit when the pressure is 'high enough.'

There's also the 105/115C switch on the head near the #4-#5 intake manifold runners. It's a 2-pin temp sensor. At 105C the auxiliary fans come on full tilt, at 115C the compressor is disengaged.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

Brian,

Sorry about the emails I sent that had nothing to do with the compressor :eek:

The wiring diagram I have is terrible but a simple test is to pull the connector off the switch. If the compressor engages, the swtich is bad.

You should also test the swtich on the drier with the blue/red wire. Jump the ends and see if that gets the compressor going. If so, the pressure switch is bad. I think you have to evacuate the system to replace the switch.

Other suspects are the cabin temp sensor, evaporator temp sensor, temp controller, pushbutton unit and the Klima relay. Diagnosis of these items is not so simple.

Have you tried with the temp wheel set to min - to the click? Have you tried in defrost mode? Are you sure you have a proper refrigerant charge?

Sixto
95 S420
91 300SE
87 300SDL
83 300SD