A/C compressor not engaging... ideas? - Page 4 - PeachParts Mercedes-Benz Forum

dieselmania · #46 10-07-2012, 07:18 PM

Quote:

Originally Posted by Merkey

Copied and pasted from the FSM....

A. Testing with electromagnetic clutch of refrigerant compressor not connected
Attention!
A prerequisite for test is perfect functioning of
refrigerant compressor activation.
For this purpose:
l Switch on ignition, push mode selection button
and (GJ for air conditioning system.
l Connect voltmeter to blue/white line (input) of
pushbutton refrigerant compressor (22) and up to
model year 84 to vehicle ground, starting model
year 85 to positive. Nominal value: battery voltage.
If there is no voltage, test air conditioning system
according to wiring diagram (refer to 83-028).
l Connect voltmeter to blue/red line (output) of
pushbutton switch refrigerant compressor (22) and
up to model year 84 to vehicle ground, starting
model year 85 to positive. Nominal value: battery
voltage.
If there is no voltage, test high pressure of air conditioning
system. Renew pushbutton switch (22) at
a pressure of > 3 bar.
Refill air conditioning system at a pressure of
< 2 bar and eliminate leak.

Maybe I am not reading this right but it seems you have it backwards. The FSM is telling you to put one probe on the trigger and for models up to 1984 the other probe to ground and look for battery voltage. This would indicate the trigger is positive. For 1985 up it says to put one probe on the trigger and the other to battery positive and look for battery voltage, which indicates the trigger is ground.

cousindave76 · #47 10-11-2012, 04:44 PM

Does your A/C system have an evaporator temperature cutoff switch? (ETR Switch). Read on if it does.

My compressor would only engage if I directly applied 12v current. I finally traced the problem to the ETR switch which is located high and right under driver foot well just under the evaporator('83 300sd). Should be closed circuit by default, opens when to cold. Mine was faulty and stayed open causing the rest of my A/C system to have no voltage. Jumped it and the A/C system worked like normal again. Replaced it and all is good.

Merkey · #48 10-11-2012, 05:35 PM

You maybe right Dieselmania...

As soon as Peachy is out of my Garage, I will investigate that, then your comment Dave!