Troubleshooting Myh 124 Climate Control

88 300E

Known:

o Shorted pin 87 to hot and compressor clutch kicks in
o Low pressure switch is made, but no Voltage making it to the switch
o Ran Impulse Counter Test at Diag connector getting one flash, meaning no errors present. I don't know if I should test temp sensors individually or if this diagnostic is adequate proof that there is no sensor trouble.
o Blower works fine and AFAIK all pods are operating correctly
o During all tests so far, the car is hotter than blue blazes, so I haven't even bothered testing the sample blower draw since the sensor is obviously hot, the clutch should be kicking in.


Since there is no Voltage making it from the CCU to the low pressure switch, then there is no signal making it to the Klima, thus the clutch is not kicking in.


I get a few minutes each evening to do a little testing, then I come in and study schematics for a few minutes. At this point my money is on the CCU as the culprit, but I want to pull the CCU and do a continuity test from the pin 7 to the low pressure switch.


Anything I missed so far? I will keep everyone posted on the process.

[J. M. van Swaay]

Don't know if this is helpful, but I recently had AC problems with my 94 E320 Wagon. Troubleshooting proved difficult because the problem was intermittant. Turned out to be a defective climate control unit. I learned that this part is also sometimes referred to as the compressor relay. Out of curiosity, I opened up the little black box. Inside I found a circuit board containing two small relays, a chip, some resistors, diodes, capacitors, etc..... This unit is more than just a relay, maybe thats why MB calls it a climate control unit.

Part number for the CCU on my car is 003 545 56 05 Don't know if your car has a similar part........

More information on my problem is available in this thread:
1994 e320 ac evap freezing up?

Second to last past details the discovery moment.


J. M. van Swaay