Compressor Clutch Issue - PeachParts Mercedes-Benz Forum

Adriel · #1 05-10-2013, 10:47 PM

Had 100*F A/C which turned out to be two problems: low on refrigerant and the clutch not engaging properly. The former is decently resolved (still a few bubbles but no longer foam) so now onto the clutch.

The clutch does not engage unless the engine is goosed to 4.000R.P.M. several times then quickly disengages. Pressure switches are new and passed with flying colors. Jumped the clutch and got nothing.

Any help greatly appreciated!

BenzTurbo · #2 05-11-2013, 05:00 AM

My compressor wont engage until 3500 ish but stays on. It does make nasty noises when it gets hot out. When i first put it on after being rebuilt, it would turn on at idle but is getting worse and worse. I bypassed my ETR switch so i only have to floor it once on my drive to get cold air. The R4 is truely a POS. I plan to do a sanden conversion before the real heat comes and it craps out. I don't think you can do anything about your problem with out removing the compressor. mine is not an electrical issue and im sure yours isnt either. It is most likely a failing electromagnetic clutch coil or the "air gap" has somehow gotten too big.

dude99 · #3 05-11-2013, 01:07 PM

I could be wrong here as I don't know a lot about A\C but if the clutch doesn't engage when you supply 12v directly to it then thats your problem. I seem to remember that you can change the clutch assembly with the compressor on the motor, but don't quote me on that. The R4 was used on a wide range of vehicles so you should be able to source the clutch from a junk yard fairly easily.

Adriel · #4 05-11-2013, 02:38 PM

Thank you all for the help!

When I did the test of the control unit, R3 to 6, the ETR switch came up faulty. However, I could not find it, nor did the mechanic even know it existed!

I rather bypass it and see how the system responds then mess with the clutch right off. If things improve then know for sure where my issue is.

Oh and my compressor does not look like the R4 as appears to be the same diameter all the way back.

BenzTurbo · #5 05-11-2013, 07:32 PM

You should see the ETR if you remove the lower dash kick panel on the passenger side. You may also want to remove the glove box liner. If you jump the 2 wires, the compressor will not turn off unless you have the acc in the off or economy mode. If you have the blower on a lower setting, its possible to freeze the evaporator up so if it is the fault, i'd replace it with a good one! Here is a pic of an R4 compressor and the ETR switch.

Adriel · #6 05-11-2013, 09:46 PM

Quote:

Originally Posted by BenzTurbo

You should see the ETR if you remove the lower dash kick panel on the passenger side. You may also want to remove the glove box liner. If you jump the 2 wires, the compressor will not turn off unless you have the acc in the off or economy mode. If you have the blower on a lower setting, its possible to freeze the evaporator up so if it is the fault, i'd replace it with a good one! Here is a pic of an R4 compressor and the ETR switch.

I remember that switch so thank you so very much for all the help! I go out now and do it, but have to move the Mercedes out of the garage well, what the heck! I can get something decent on!

Oh, and had the wrong picture, so thank you for clarifying that. Brand new, so hopefully do not have to mess with it...

Adriel · #7 05-11-2013, 10:12 PM

Well, jumped the two wires and nothing! So is it a bad compressor relay then?

Clutch is new so really doubt it being an issue.

Thank you all in advance!

oldiesel · #8 05-11-2013, 11:03 PM

Most A/C compressor clutch units have a way to adjust the air gap,and if the air gap is too great they will fail to engage.You will have to look up how your unit can be adjusted and what the air gap is supposed to be.

BenzTurbo · #9 05-11-2013, 11:29 PM

No problem!

Try turning the key to the 2nd click but don't start it. Wait for the glow plug relay to "click" off and turn your a/c on. Maybe put the blower on low so its quieter. You should hear the compressor clicking when you turn on and off the a/c and the magnet pulls the clutch in. If not, reach in and try helping the clutch by pushing it in. (with the engine OFF)

If it does engage with a push, the clutch magnet is most likely toast or the air gap is too big for magnet to overcome. You can try this test with jumper wires from your battery directly to your clutch and if you have the same results, you can be 150% sure your cars wiring is not the problem!

Adriel · #10 05-13-2013, 10:33 AM

Thank you all for the help!

Figured be good to repeat than miss something.

I finally got my friend born in '41 to who is a A/C technician to hook up his gauges on Friday (not in the best shape, gets tired easy, but still works as if he is not retired). It showed about 200P.S.I. on high side and vacuum on the low. Added a can as that is what he said to do. It was then found the clutch was not engaging easily (several bursts to over 3.500R.P.M. to get it to snap) and quickly disengaging.

Tram said add another can. That didn't work so well as there was no instructions how to get the plastic tab out so the build in gauge kept popping. According to that the pressure is no more than 45P.S.I. at 95*F. The refrigerant still looks foamy.

The trigger dispenser is now repaired so it is proper and bought another can.

The cans we are using add about an ounce of oil so the system has at least five to six, plus the two tablespoons.

I pressed on the clutch with the system on and nothing happened.

I can't jump the compressor directly as have to strip a lot of stuff out of the way. Did it indirectly by back probing and nothing. I have thin hands but the connector keeps hitting the fender. I hate to pull it off and not get it back on!

What I am getting from what you all are saying is the A/C replay is bad? Or is it the few month old compressor? I HIGHLY doubt the latter.

BenzTurbo · #11 05-14-2013, 02:27 AM

Hmm, thats odd why it will not stay engaged. You should try jumping the compressor. That will really narrow it down to the compressor being an issue or a sensor/ bad connector on the car. Do you have any small alligator test leads or something to connect to the compressor? I find it easy to access the compressor connector from under the car. You can use the glow plug relay for a +12v test location because it always has power and ground it to a power steering pump bolt or something. The connector that goes in the side of the compressor gets a lot of oil and dirt in it that could cause an issue so its not a bad idea to unplug it and clean it anyways

Adriel · #12 05-15-2013, 11:54 AM

Quote:

Originally Posted by BenzTurbo

Hmm, thats odd why it will not stay engaged. You should try jumping the compressor. That will really narrow it down to the compressor being an issue or a sensor/ bad connector on the car. Do you have any small alligator test leads or something to connect to the compressor? I find it easy to access the compressor connector from under the car. You can use the glow plug relay for a +12v test location because it always has power and ground it to a power steering pump bolt or something. The connector that goes in the side of the compressor gets a lot of oil and dirt in it that could cause an issue so its not a bad idea to unplug it and clean it anyways

Thank you so very much for all the help!

I jumped it several times and nothing. I have an adrenaline rush that I have not experienced since I shocked myself with 10 amp 120volt! The crackle of welding sure gets my attention! Just not a lot of room to get a lead from the battery all the way down in the hole. I would figure jumping the compressor should turn it on, right?

At this point, I am seeing the dollars add up. If I have to pull the compressor that means I have to have the system vacuumed. That then opens up a can of worms as then I have to decide if I want to stick with the R134a or go R12a. I know the "risks" with R12a but rather do that than leave something in the atmosphere that will affect future generations (following the concept of Chief Seattle). Plus, works better than R12 or R134a and extends the life of the compressor. Oh, and the best part: it costs less!

Air&Road · #13 05-15-2013, 01:20 PM

If jumping 12V directly to the clutch does not cause the clutch to engage, the problem is the clutch, not the compressor. The clutch can be replaced or the air gap adjusted. If this is the situation, there is no need to replace the entire compressor.

Doktor Bert · #14 05-15-2013, 07:31 PM

Quote:

Originally Posted by Adriel

It showed about 200P.S.I. on high side and vacuum on the low.

This would indicate an obstruction. Since I have no idea what car you are working on, I will address this based on my 1978 W116.

When my expansion valve stuck closed, I had similar pressures to what you describe.

After I flushed the system out with the proprietary A/C flush, replaced the expansion valve and added the correct amount of mineral oil (R-12 system) and charged the system with 2.6 lbs of R-12 (I use no substitutes) and allowed the system to stabilize.

I then removed the 'Blanket' from the ETR and dialed in compressor cutoff at 35°F in the center vent @ 85°F ambient.

Pressures recorded were 150-170 psi on the high side and 20-30 psi on the low side.

NOTE: pressures will drop on the low side and rise on the high side until the point of compressor cutoff, then pressures will stabilize (equalize) on both sides during the shutoff period.

Doktor Bert · #15 05-15-2013, 07:33 PM

Quote:

Originally Posted by oldiesel

Most A/C compressor clutch units have a way to adjust the air gap,and if the air gap is too great they will fail to engage.You will have to look up how your unit can be adjusted and what the air gap is supposed to be.

Factory specification on the R4 is .020" to .040" but I set them at .015" on all A6 and R4 compressors.

The tool to install the clutch is needed to set the air gap....