W124 compressor won't start - I'm stuck - PeachParts Mercedes-Benz Forum

pdrayton · #1 05-31-2007, 03:37 PM

AC has been working great on the 1992 300D 2.5 W124 until a few days ago it just quit. No apparent reason.

I have:

Checked the fuses 5, 7, 12 and the OVP fuse. All good.

Shorted the temp and pressure switches - no cut on

Tested the interior sensor by putting the piece of paper over it (as in the FSM)

Tested pressure - with the ac off (obviously, becuase the compressor won't kick in) the pressure is up around 100PSi. Is that OK? I know it is normally high when the compressor is off and then it drops down again, but I don't know how high is too high.

I put a volt meter across that resistor behind the driver headlight and it didn't have any voltage.

The CC control buttons in the cabin are responsive - the fan switches on and off when I push them, so I am thinking it is not them.

I'm stumped as to what to check next. The FSM procedures seem to need that funky connector box, and they seem kinda overwhelming.

Any suggestions? Open the windows? Yeah, tried that. Not good enough in Florida...

rrgrassi · #2 05-31-2007, 05:49 PM

Did you short the switches themselves or did you jumper the wire leads? Did you check for power at the compressor? If you are getting power there, even with the temp and pressure switches connected again, it could be the clutch on the compressor went out. IIRC, you may have a faulty KLIMA relay instead.

pdrayton · #3 05-31-2007, 08:29 PM

Thanks Rrgrassi for the reply.

I don't know how to check for power at the compressor. I looked, but didn't see anything obvious, and I didn't see how I could test it anyway with the car running. Any tips?

What does IIRC mean please? And is there a way to test the Klima?

Thanks

pdrayton · #4 05-31-2007, 08:30 PM

To answer your question though

- I took the leads off the temperature switch (the black switch with the 2 spade connectors on top of the drier) and jumped them.

The other switch (red - pressure?) I jumped them while they were still on the switch.

P.E.Haiges · #5 06-01-2007, 12:09 AM

pdrayton,

Connect a wire from the + terminal of the battery to the magnetic clutch terminal. U should hear the magnetic clutch engage. U should do this with out the engine running.

If the clutch engages, the problem is somewhere else. If the clutch does not engage, the clutch is the problem.

P E H

pdrayton · #6 06-01-2007, 07:41 AM

P.E. H. - Awesome! Thanks, I'll give that a try.

Another symptom (perhaps) has shown up - the car won't stop when switched off at the ignition. I know on my 240D is shut down by vacuum, so I am thinking there is a vacuum hose loose. It's the wife's car, so I don't have it with me at the mo, but will look for loose vacuum hoses.

Is it possible that vacuum issues could be causing the a/c not to work?

P.E.Haiges · #7 06-01-2007, 09:41 AM

Yes, vacuum problems could cause the AC not to work. The AC system is highly vacuum controlled.

Has any feel changed in the foot brake? If it seems harder to push, the brake booster is getting less vacuum. This could be caused by the vacuum pump going bad or a leak in the vacuum line fron pump to the booster.

P E H

pdrayton · #8 06-01-2007, 09:53 AM

I will apply the Mityvac to said recalcitrant vehicle without mercy apon it's return to the stable. Thanks for the help.

pdrayton · #9 06-01-2007, 07:06 PM

OK. So I put 12 V to the left most connector on the 3 prong connector on the compressor, and the clutch engaged. So the clutch is OK.

I started the car up and there was no voltage to any of the pins on the compressor connector. So the compressor is not getting the instruction to engage.

Combine this with the fact that the car keeps running after the ignition has been turned off, and the cause of all the problems is.........

I've tested the vacuum system (as far as I know). The vac pump is putting out 25 inHg. of the 4 tubes going out from the vac pump - the one going to the turbo and egr doesn't hold vacuum (which I believe is normal), the other 2 hold vacuum so I don't think the car switching off is related to the vacuum. But what else could it be?

Here's me wishing there was a simple solution that some guru could tell me about. It's worth a 6 pack of your favorite beer! Seriously.

P.E.Haiges · #10 06-02-2007, 02:19 AM

pdrayton,

With engine running, remove the brown vacuum line from the shutoff device on the IP and connect it to the mightyvac. U don't have to remove the line at the IP, U can remove at any connection going back toward the key switch.

Now turn off the key switch and observe the mighgtyvac dial. It should be reading a vacuum. If not, there is a leak somewhere. If U connect the vacuum line from the IP shutoff device and apply vacuum from mightyvac to that line the engine should stop.

These tests will show whether the shut off device is working and if it is getting vacuum from the key switch.

P E H

pdrayton · #11 06-06-2007, 01:09 PM

Turns out the vacuum shutoff valve is shot. Doesn't hold any vacuum. I've ordered antoher one. Looks like I have to take off the ALDA to get this valve off. Hmmmm, painful.

Anyway, I got the AC working again. I found out that there is a fault code test you can do with the x11/4 connectino (or whatever it is called). It is wrongly listed in teh FSM as 83-503. it is actually 83-603. Anyway, it lists all the fault codes for the AC components.

But I foudn that after I took out the Klima relay to check it's fuses and put it back again, the compressor switched on fine and the AC is working 100% for the past 3 days. So I am wondering what fixed it. Maybe a bad connection to the Klima, or maybe it is just forwarning that the Klima is on it's way out. .....

Thanks for all the help. If there are any tips for replacing the shutoff valve please let me know.

Paul