92 400e a/c compressor won't engage - PeachParts Mercedes-Benz Forum

gregoryyoder · #1 07-11-2010, 02:29 PM

I have a 92 400 E. The A/C compressor won't engage. I'm pretty sure the compressor is OK. I had the R134 pumped out and refilled. The pressures are OK and there are no leaks. It's somewhere in the circuity.

Thanks
Greg

macdrone · #2 07-11-2010, 05:00 PM

Pressure sensor on the drier may be bad mine was. Gorr take out freon again to replace. Compressor must engage to get the proper amount of freon in also btw. Need 35 on the low side with compressor engaged at 2000 rpms or your system will never work correctly.

#3 07-11-2010, 06:39 PM

Are you sure that the compressor is not engaging momentarily and then kicking out? Watch the front of the compressor while someone starts the car and then turns on the climate control. If it kicks in momentarily, then it is likely a belt or clutch slippage issue.

There has been massive discussion of this system here on the forum if that turns out to be the problem.

Best of luck,

emerydc8 · #4 07-12-2010, 05:15 AM

I had this happen on my 400E. I don't know if this will hurt the compressor or clutch (it didn't seem to hurt mine), but I emptied a can of contact cleaner in between the clutch and pulley, cleaned and reseated both electrical plugs to the compressor, and lightly tapped the front of the clutch plate a few times with a ratchet. I think the engine was actually running and I was calling for cold air on the a/c when I tapped the clutch plate. This was at the recommendation of the dealer's shop foreman. He said that sometimes the clutch sticks and this will unstick it. I don't really know which one solved the problem, but it started working after that. I'm glad it did, because the foreman told me that trying to repair the a/c clutch on the 400E without taking the compressor of the car is not a fun job.

Here is a good link on clutch problems with an idea from Deanyel that I would consider.

Intermittent A/C Clutch - A Relay, perhaps???

Quote:

Not sure, but it's possible that the clutch slippage fault requires getting both signals and finding a disparity between the two, as opposed to just not getting one of the signals and being unable to do the comparison. Not specifically familiar with your car but shouldn't be hard to replace the speed signal sensor, normally doesn't require removal of the compressor, but the first step would be to have a look at it, to see if the connections look good and wires not bare etc. One of things that I've done, and I'm sure this in primitive and unelegant, is to run a 12v wire off the fuse box (proper amps) to the compressor power line to see if the clutch engages, stays engaged and cools. If so you know you don't have a compressor problem, clutch engagement problem, clutch gap/shim problem etc. This confirms that you have an electrical problem - that the signal is simply not getting through the morass of tests in the system.

mlozzi200478 · #5 07-17-2010, 02:11 PM

first i would open the hood,place your hand on the ac compressor clutch,it should spin freely with your hand,with no scraping at all,it will move easily,if its hard to turn or grinds while turning,the clutch is bad,also if the clutch is bad,it will throw the belt off,another issue is the pressure sensor,if there is a tiny leack,there will not be enough pressure on the switch to engage the clutch.did they do an evac then perform a pressure test,then leave for a while to see if the pressure has dropped at all?if your positive there are no leaks,check into the ac pressure switch.sometimes they go defective.,make sure all wire connector ends are tight,no loose connector ends,and all the wiring looks tight/sealed.another thing is checking the operation,of the climate control head unit.sometimes the saldor fractures internally,causing no power to relay over the switches.you can resolder the pins,or purchase a reman,unit.good luck.