A/C suddenly stopped working yesterday - compressor shot??? - PeachParts Mercedes-Benz Forum

Jetmugg · #1 08-04-2010, 11:29 AM

I have a '93 190E which has been refitted with an OM602 turbo / 5 speed drivetrain.

The A/C has worked well for the last 2 years, since I put the car back on the road. At that time, I put in a new condenser, expansion valve, and drier. The system was evacuated, filled with the proper amount of oil, and charged with R-12. It has worked as intended up until yesterday.

It was extremely hot here in St Louis yesterday (102F actual temp, "heat index" up to 117). Anyway, as I was running some errands yesterday in the early evening, the A/C was working fine, until I pulled into a friend's driveway, shut the engine off, and the car sat for maybe 5 mins.

When I restarted it and engaged the A/C, I heard a "chirp" sound, and then I had no A/C the rest of the way home. When I arrived home, I popped the hood open, and with the engine running, temporarily jumpered around the pressure switch next to the drier. Again, the compressor "chirped" as the clutch engaged. I immediately un-jumpered the connection, and now assume that the compressor is shot.

Could an excessively high head pressure (related to the high outside and underhood temps) have caused the compressor to fail, or was it just a coincidence?

I have 2 "spare" compressors on the shelf - is there a reliable way to test them before installing them in the car (I will flush the whole system and replace the drier and expansion valve)? Any advice on getting the system back up and running would be appreciated.

SteveM.

LCA078 · #2 08-04-2010, 11:43 AM

Before you condemn your compressor, take look at the clutch. My situation was very similar to your in that my "compressor" was locked up. Turns out, the electromagnet coil melted and dripped molten plastic between the coil and pulley when shut down. When I tried to start back up a few hours later, the compressor was locked. After I removed the compressor, I found out the compressor was fine, it was the pulley stuck to the electromagnet.

Jetmugg · #3 08-04-2010, 11:51 AM

Excellent idea - I will certainly check the clutch ocondition before getting any deeper.

I will also check the pressure in the system.

SteveM.

#4 08-04-2010, 12:14 PM

With engine off, turn the clutch at the foreward most portion of the compressor in front of the belt, by hand. If it turns freely then there is likely something slipping which is causing the rotational sensor to mismatch engine speed. In this case the system shuts off the a/c to prevent distributing debris throughout the a/c system. A loose belt, bad tensioner, bad or slipping compressor clutch, a bad sensor or a worn compressor are all things that can cause this to happen.

Start by checking tensioner and clutch gap. Occasionally if the clutch is the culprit, spraying it down with Brake Kleen will correct the situation.

Hope this helps,

Jetmugg · #5 08-04-2010, 12:25 PM

Thanks Larry - I know you are a guru of this stuff.

The sudden nature of this failure, in conjunction with the very high ambient temperatures yesterday, have me puzzled. It was working, then the car was shut off, and 5 minutes later, the A/C would not work at all.

I will take your advice to heart, first checking for resistance while turning the input portion of the clutch by hand, then checking the clutch condition and gap.

The tensioner and belt are relatively new, I don't suspect them.

Does the fact that I was able to jumper the pressure switch and cause the clutch to engage (with the dash controller set on A/C) provide any clues?

SteveM.

sixto · #6 08-04-2010, 04:14 PM

It tells me system pressure is too low or too high or the switch is bad.

Sixto
87 300D

Jetmugg · #7 08-04-2010, 08:46 PM

It does appear to be a problem with the clutch.

I can turn the compressor by hand and it feels smooth.

If I start it up cold and switch on the A/C, the clutch will engage briefly, then I can visibly see it start slipping, then it dis-engages (presumably due to the differential rpm's as suggested by Larry Bible).

I'll try to use the brake cleaner trick, but I'm not too confident about that working.

Next issue- is it possible to change the compressor clutch without losing the charge in the system? Are there any seals on the front of the compressor that need to be opened in order to change the clutch?

SteveM.

#8 08-05-2010, 07:23 AM

Yes it's possible to change the clutch, but don't get the cart in front of the horse. There are many other possibilities for tripping the rotational sensor circuit.

Assuming that it is indeed the sensor tripping, possibilities are; clutch, belt, belt tensioner or just a worn out compressor. The compressor can wear to a point where the innards move fore and aft due to thrust upon engagement. This can fool the sensor. A remote possibility can be the sensor itself.

Check belt tension and belt condition.

The good news in your last post is that the compressor is turning smoothly.

It would be a good idea to put a set of gauges on it and check pressures. Record high and low pressures if you can get the clutch to stay pulled in.

Jetmugg · #9 08-05-2010, 07:58 AM

More good advice, Larry.

Hopefully I can find the time to perform some more diagnostics and get a set of gauges on her this evening.

If the compressor is worn to the point where it makes/loses contact with the sensor, should I be able to feel forward/backward movement by grabbing the front "hub"?

Steve.

funola · #10 08-05-2010, 08:50 AM

Are the clutch plates metal to metal or should there be frictional material on one of them? On my R4's (2 that I have taken the clutches apart), there is no friction material that I can see, unless it's worn off. If your clutch is slipping, if there's oil in there brake clean should help. Or the gap maybe too big. If the surfaces are glazed, slippiping 60 grit paper in there to rough it up will help.

#11 08-05-2010, 12:24 PM

No you can't feel the thrust movement at the clutch. It is internal.

There are posts on here that give pin numbers and so forth for replacing the Klima relay with an ice cube relay to defeat the rotational sensor circuit.

Jetmugg · #12 08-05-2010, 12:30 PM

I would prefer to "allow" the system to work the way that MB designed it.

If the clutch is slipping, I want to fix that condition so I can get the proper rpm's from the compressor.

In the end, I'm not above "forcing" the system to work the way that I want it to, but if I can figure out exactly what's happening and why, I'll feel a lot better about it.

SteveM.

francotirador · #13 08-05-2010, 06:34 PM

Quote:

Originally Posted by LarryBible

With engine off, turn the clutch at the foreward most portion of the compressor in front of the belt, by hand. If it turns freely then there is likely something slipping which is causing the rotational sensor to mismatch engine speed. In this case the system shuts off the a/c to prevent distributing debris throughout the a/c system. A loose belt, bad tensioner, bad or slipping compressor clutch, a bad sensor or a worn compressor are all things that can cause this to happen.

Start by checking tensioner and clutch gap. Occasionally if the clutch is the culprit, spraying it down with Brake Kleen will correct the situation.

Hope this helps,

I don't want to hijack this thread, but I'd like to know the outcome as I'm experiencing the same issue. My a/c just stopped working today and I'm clueless. I turned the clutch as you suggested to the OP and it turns freely. I'd like to know if a lack of refrigerant will cause the compressor to shut down suddenly.

Jetmugg · #14 08-05-2010, 11:21 PM

Update - I had a little bit of time to hook up some gauges (Robinair, so I trust the readings).

I selected A/C and minimum temperature before starting the engine. The guages were already hooked up, but shame on me for not noting carefully enough what the static pressures were before starting the engine. I think it was about 90 psi. on both sides.

Anyway, I started the engine, then walked around to peek at the compressor. After about 20 seconds or so, the clutch engaged (should it take that long). After that, the clutch stayed engaged.

The high side pressure got up to 200 psi. The low side pressure went down to about 45 psi. This was probably after 1 minute of running or so. The ambient temperature was roughly 80F. I didn't have a chance to check the temperature of the air at the dash vents, but it was suitably cold.

Do my pressures look OK?

SteveM.

sixto · #15 08-06-2010, 12:10 AM

Klimas prior to 1990 have a 10 second compressor delay after starting the engine.

Sixto
87 300D