'85 300D with Klima relay, no power to A/C compressor. - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 04-15-2016, 01:43 PM

I have no power to the A/C compressor, and have replaced everything I know of. I replaced the Klima relay, the CCU, checked the fuses, and checked the monovalve. I tried five different CCU's I had, and no change. I tried a known good Klima relay, and still no power. With A/C selected and the temp wheel all the way on blue, I have power at the monovalve connector. The fuses are good, even the one for terminal 86. I can put +12v to the compressor coil, and it blows cold. I even bypassed the compressor switch, and still no power to the compressor. Anyone know where else I can check?

Volvo Diesel · #2 04-15-2016, 02:07 PM

By the compressor switch, do you mean the one on top of the valve cover? If yes, you can stop reading now, because what follows won't be helpful. If not....

What about the compressor cut-off switch on top of the valve cover? When mine started to fail it caused the compressor to cut on and off very quickly; moving/ messing with the connector would usually solve the issue. Finally, the compressor wouldn't come on at all, but when I unplugged the switch the compressor worked fine. I just left it unplugged and zip-tied the connector to some vacuum lines (the cut-off feature doesn't matter to me) and it still works fine.

Good luck.

SD Blue · #3 04-15-2016, 02:09 PM

From what I gather of the FSM schematics, the 85 is a little different. The Compressor Kickdown Cut-out Control Unit provides power to the A/C clutch. It is also on a different fuse F11.

ROLLGUY · #4 04-15-2016, 02:27 PM

Thanks for the great tips. The switch I bypassed was the pressure switch on top of the drier. I had not thought about the compressor cut-out switch on the valve cover. I will check it out, thanks.