Replacing AC Compressor Clutch

[JoeMB]

Could someone inform me how to replace an AC Compressor Clutch on a 1984 300D Turbo?

This morning, the local Mercedes Shop inspected my entire air conditioning system and said that the compressor clutch was not operating. They informed me they could not order or replace this one particular item, but could order the entire compressor, receiver/drier, expansion valve and recharge the system. This would be very costly.

I have read through the threads on the message board and noticed that some people have replaced the clutch, but I could not find any specific information about the process, tools, or how they did it.

[Pete Burton]

My guess is you have an R4 compressor on it. I think you can fashion a spanner to provide a counterhold to the very front of it (the triangular shaped plate) and remove the nut. But, I'm sort of guessing, do a search, you'll find more. Also, make sure the compressor itself turns freely, as if the clutch failed because the compressor siezed, you'll be wasting your time.

[billrei]

Is the clutch not working or not getting power? It's easy to check the clutch operation yourself. Just hook a 12V source (battery) to the 2 pins in the plug socket. You should hear a the clang of the electromagnetic pulling in the clutch plate. If you hear that noise then you know your problem is in the climate control not sending a signal, not the clutch.

[dannym]

as if the clutch failed because the compressor siezed, you'll be wasting your time.

If the compressor siezed then the whole system is fouled. You would then need to replace the compressor, condenser and the filter/dryer. Then the remaining components, core, tev, etc.. would need to be flushed. Actually the tev is a $20 part so just replace it anyway.
You without a doubt want to make sure the compressor is still working.

Like Pete said you can "make" a spanner wrench to hold the pulley in place while you remove the clutch nut. I would spray the crap out of it with penetrating oil like PB Blaster over the course of a day or two. Some light blows with a hammer wouldn't hurt if there's enough room.

My experience with clutches is they are a PITA to remove. especially ones that have been on for 20+ years. Not that it would happen to you but I more often than not have broken or bent the compressor shaft. I would STRONGLY encourage patience when working on this.

Replacing the compressor would be best but the R-12 throws a monkey wrench in that.

Good luck.

Danny

[billrei]

I've had good results with a R12 replacement. http://www.es-refrigerants.com/ . I have both my 250SE and W123 running on it with no problems. I used the lastest esther based oil which eliminates the corrosion issues with R134.

[tangofox007]

Originally Posted by dannym

Replacing the compressor would be best but the R-12 throws a monkey wrench in that.

Could you elaborate? About the R-12 and the monkey wrench.

[Wasuchi]

Are you sure the system is charged? If it isn't the clutch won't work, it still will if you hook the 12v to it like billrei said, but not on it's own.

[JoeMB]

Thanks for all the posts concerning my inoperative AC compressor clutch on my 1984, 300D Turbo.

I did take my car this morning to the Mercedes Shop and they ascertained that: there was sufficient charge at the low pressure switch, that there was both power and ground at the A/C clutch. They informed that the A/C clutch was not engaging.

I examined the compressor and found it was manufactured by General Motors (GM) and model number 111350. It also said Harrison on the label.

[Pete Burton]

Good, then it is an R4 compressor. I replaced mine years ago with a Four seasons rebuild, only $97. If the compressor is good, you should be able to turn that triangular plate by hand. But before you change the clutch, check the resistance across the 2 clutch terminals. Should be a bit less than 1 ohm I think. If it IS that, test it again by jumping it direct from the battery (briefly). Reason is, that clutch takes a lot of current, and just because you have 12 volts doesn't mean you have 15 amps or so going through it.

[dannym]

Originally Posted by tangofox007

Could you elaborate? About the R-12 and the monkey wrench.

Most people don't have the necessary equipment to work on R-12 systems. Unless of course you don't give a crap about the environment and just vent to the atmosphere.
It's not like you can walk down to the local Auto Zone and buy gauges, refrigerant, etc..

Monkey wrench=not impossible just a little more difficult.

Danny

[SD Blue]

Originally Posted by billrei

I've had good results with a R12 replacement. http://www.es-refrigerants.com/ . I have both my 250SE and W123 running on it with no problems. I used the lastest esther based oil which eliminates the corrosion issues with R134.

Your link only takes us to the home page. Which "replacement" did you use?

[JoeMB]

Does the "Air Gap", the distance between the A/C compressor clutch plate and the compressor clutch rotor normally increase with age and usage? My vehicle has 177,000 miles on it.

According to the shop manual, this gap should be from 0.5mm and 1.0mm, on my 1984 300D the gap is closer to 1.5mm. The manual says if this gap is too large, the electromagnetic coil may not be able pull the clutch plate and engage the compressor. Therefore, I am thinking that I need to adjust this air gap back to the correct tolerance and do some testing.

The resistance of the electromagnetic coil is 3.5 ohms, which is the same resistance of another coil in my other vehicle with the same compressor (GM R-4).

If anyone has any experience about this please let me know. I am new at working on this type of problem.

[Pete Burton]

It's very possible that resistance is OK. I know it takes several amps, obviously I was thinking more, but 3.5 ohms would give about 3.5 amps. Yes, the gap does increase as it wears. So, first with engine off, see if you can rotate triangular plate easily by hand, you should be able to. Then, run jumpers to the clutch and put your DMM on 10A setting inline. Then, push the triangular plate in real slow and see if it doesn't "jump" closed when you close the gap up about halfway.

[JoeMB]

Thanks for all the information about the compressor clutch, it has been a great help in narrowing what the problem most likely is.

This weekend I followed Pete's suggestion and ran jumper wires from the battery, with a Digital MultiMeter inline, to the compressor clutch. The compressor clutch immediately closed and the amperage was 3.38 amps. I tested this several times with the same result. This clutch closed even though the "air gap" is 1.5mm, which is much wider than the shop manual specifications.

Although the compressor clutch closes during those tests, is it possible that once the car is running, with the A/C on, the clutch is slipping? The air conditioning does seem to put out somewhat cool air, but never cold.

I ordered a compressor clutch tool kit which contains a "clutch hub holding tool", "compressor plate removal tool", and a "compressor plate installer tool". Using these tools I should be able to remove the clutch plate, and do an inspection of the plate wear, and then re-install the clutch plate with the correct air gap. Unfortunately, the tool kit will take 2 -3 weeks to arrive.

[Wasuchi]

The somewhat cool air sounds a lot like the bad expansion valve I had last summer, the air was cooler than the outside air but cooler than 95-100 degree air doesn't really cut it when you're sitting in the sun. I replaced the expansion valve and dryer and it worked 100% better, it's really cold now! The guy that did it also flushed the whole system a couple times because it was really dirty. He was also the only guy that I could find that didn't insist on converting it to R-134.