AC Clutch Intermittent (A/C, Air Conditioning, Compressor, 1984 300D Turbo) - PeachParts Mercedes-Benz Forum

littlerobot · #1 06-19-2010, 12:06 PM

I've searched the forums, and haven't found this exact problem.

The compressor clutch sometimes engages, and sometimes does not when starting the car, which leaves me never knowing if I'm going to have a sweaty ride or not. However, I'd say most of the time it does not engage. Turning the ignition off and back on seems to have no effect on the problem. Once on or off, it does not intermittently engage. It either stays on, or stays off, until I turn the car off. So, I need some advice on where to look first. Here's what I assume:

1. The temp dial on the climate control unit, or some other part of the CCU may be bad.

2. A short or faulty wiring connecting to the compressor.

3. Compressor clutch is faulty.

Is there anything else it could be? Is it possible to replace the clutch without replacing the compressor? Where should I start?

*I have cleaned the clutch with brake cleaner to make sure it wasn't dirty or greasy.

ashedd · #2 06-19-2010, 09:10 PM

I used a piece of plastic water line that builders use nowadays... just something I had laying around. Do I need to replace it with something better Larry?

littlerobot · #3 06-20-2010, 01:34 PM

Yes, but that sensor you speak of, isn't it overridden if the climate controls are on manual intead of auto? If I rotate the temp dial to cold, and engage the blower motor on full-blast, then that sensor is no longer involved in the equation, right?

That said, I'll do what is suggested. It couldn't hurt, right? But I'd still like an answer to the above question if anyone happens to know.....

BoiseBenz · #4 06-20-2010, 03:23 PM

Do you have good (read: new) brass/copper fuses? Did you inspect/swap the ice cube relays (one for aux radiator fan, one for compressor clutch)?

littlerobot · #5 06-21-2010, 12:05 PM

I have never heard of the "ice cube" relays. Where are they and how do I get to them?

The aux radiator fan works. I have new fuses, and are willing to use them.

, but is the compressor clutch fuse somewhere else besides the fuse box? I'm a bit confused.....

BoiseBenz · #6 06-21-2010, 12:52 PM

Quote:

Originally Posted by littlerobot

I have never heard of the "ice cube" relays. Where are they and how do I get to them?

Under the hood, atop the left wheel well, under a 4x5" (100x125mm) black plastic cover.

littlerobot · #7 06-21-2010, 01:04 PM

You're right Larry. I've removed the glove compartment and are making the changes you requested now.

Boise Benz: I've found the box you described. Underneath the cover are two silver boxes with relay diagrams on top. I can pull them off easily. Are the fuses you describe inside the silver boxes? There doesn't seem to be an easy way (on first inspection) to get inside them....

littlerobot · #8 06-21-2010, 01:12 PM

Duh. I get it. The relays (two silver boxes) resemble ice cubes, thus "Ice Cube Relay". I have a feeling I should be carrying extra relays with me for these kinds of problems?

littlerobot · #9 06-21-2010, 03:43 PM

1.The 'ice cube' relays are both working. I put in new one and switched them around: the aux fan came on with both relays. The compressor clutch did not.

2. I replaced the climate control unit with a new / rebuilt CCU. No change in temp and compressor clutch is still not engaging.

Is there any way to manually engage the clutch? Wire jump?

Is it possible to replace the clutch and not the entire compressor, or is this a sign of a failing compressor?

Climate issues are a pain. Not as big of a pain as changing the starter motor, which I did last week.

littlerobot · #10 06-21-2010, 08:02 PM

Larry,

There are two lead wires on the side of the compressor. If I disconnect them from the compressor and clip my voltometer wires to them and turn the ignition to activate the cars electrical system (but not start it), should my multimeter read 12 volts? I'm thinking of trying this.

littlerobot · #11 06-21-2010, 08:28 PM

Also, where is the low pressure switch?

leathermang · #12 06-21-2010, 11:02 PM

By low pressure switch... if you mean the one which will turn off the system in the event of refrigerant loss... it is typically on top of the Receiver Dryer. It plugs into the system.. so can not be taken out without losing refrigerant... but the other switch there is a temperature switch which can be replaced without loss of refrigerant...
Some cars may have more than one which would be called something like that... and it would be used to activate the clutch on the compressor...
You may have to be more specific in the question to get a solid answer.

littlerobot · #13 06-22-2010, 03:20 PM

okay:

1. I jumped the pressure switch on the receiver / dryer. Still no clutch engagement.

2. Hooked a multimeter up to the wires that plug into the side of the compressor (I assume these power the clutch to engage / disengage) There appears to be no voltage getting to the compressor clutch.

Geez, what the heck is the next step? This appears to be a voltage issue, yet the ice cube relays are fine, it appears the pressure switch is also, so where the heck could the problem be?!?!

Am I correct in assuming the next step is to hook the stupid compressor straight up to the battery and see if it clicks?

leathermang · #14 06-22-2010, 05:14 PM

That is the logical thing to do... try to separate the system components and test them one at a time....

littlerobot · #15 06-22-2010, 05:51 PM

okay, after buying a more reliable multimeter:

1. Compressor is getting power.

2. Clutch not engaging.

So......bad clutch. Question is, do I buy a brand new clutch, or pull one from a yard. Also, having never done this before, how difficult is it on a scale of 1 to 10?