Hello All, I have an '87 190E 2.6 and am having some air conditioning problems. The compressor clutch disengages after running the system for a little while (5-10 minutes). Initially everything works and there are no funny noises. I have checked the LP switch and it has continuity. When the clutch quits, I have to shut the car off and restart to get the ac clutch to engage. But at this point I hear some bad noises and the clutch will disengage pretty quickly (under a minute). When it disengages the rpms will go up for and then stabilize. I'm assuming that the Klima relay is detecting belt slip and is cutting the clutch. Does this all sound right? Also, if I let the car sit overnight, the compressor will again work for about 5-10 minutes before disengaging...then return to the 1 minute cycle. During the start from cold, 5-10 minute run the compressor will be quiet, it is only during the under a minute engagement when hot, does it make bad noises. Does this sound like a dead compressor? If this is the compressor, I'm estimating in my mind that it will be about $1000 to get it fixed. Does this sound about right? BTW it is a R-12 system. Thanks.

If it is low in freon, it will do that along with a loose or dirty belt. Did you read this?
http://www.peachparts.com/diy_stevebfl_0.htm

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J.H.
'86 300E

Yes, I fully expect that the problem is a loose, bad or greasy belt. Something is making it slip which trips the sensor.

Good luck,

I really hope that it is a greasy or dirty belt....wouldn't that be nice. Unfortunately, the belt has less than 10K and the tensioner was replaced at the same time. Right now the pointer is still showing at the top of the scale and is really tight to the touch. I'll look a little closer to see if there is any oil or dirt on the belt.

Well, I checked and the belt is tight and clean. Whne the compressor spins up it does give a bad bearing type noise....of course that goes away when the clucth disengages so I don't think it is the ac clutch bearing. Should I convert the car to 134a since it all has to come apart and since R-12 would amount to at least $350 of the repair?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=46094&item=2469852882

Get certified and purchase it on ebay. The above link shows about all you will need for probably under $60 (based on where the bids end).

Sounds like your compressor is on it's way out.

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Jim

If someone is telling you that it will cost $350 for R12 run, don't walk, away from them and don't ever do business with them again. They are STEALING FROM YOU!!!

Follow engatworks advice and buy your own R12. Additionally, from what you've said so far there is not yet any evidence that you even need any refrigerant. Diagnose before you act.

The first thing you need to do is put gauges on the system and see what the pressures are.

Check your sensor wiring to make sure it is all in good shape. Your symptoms still sound like a slipping belt. Possibly the sensor is flaky or wiring to the sensor is flaky.

Look before you leap,

Okay, here is an update...so to speak. First of all I am under the assumption that if a compressor makes bad bearing noises, it should do that everytime it is switched on. Since my car made the noises only when hot....something did not seem quite right. I am hopeful that Larry is right and he definitely has 10,000 fold my experience. So the good news is that I believe the compressor is fine...the bad news is that I am almost sure my waterpump is on it's way out. There is some play when I grab the pulley and the scraping noises seems to be coming from the waterpump area. The way it looks, when the compressor is switched on the extra load on the belt must put additional load on the waterpump...causing the bearing to squeal, creating more resistance and causing the belt to slip.....thus triggering the Klima relay. Does all this sound plausable?

I replaced the belt on my 1990 350SDL a couple of years ago and had simular problems. I did mine in the late fall and did not relate the problem in the spring when I started to use the air. I tied to determine what the cause could be but had to give up. It went to Mercedes and the belt was changed and has worked flawlessly since. I was told the wrong belt was installed. Hope thus helps.

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Who needs spark plugs.

Here is an update. I took the car into the shop as I didn't have the time to tear apart the car. The diagnosis was a bad ac compressor. The compressor, receiver/dryer, and the rear manifold was changed. Now I once again have cool air....too bad I also have an empty wallet.