a/c compressor not kicking in - Page 2 - PeachParts Mercedes-Benz Forum

pmckechnie · #16 01-10-2007, 07:32 AM

Maybe I missed it but did you watch very closly at the A/C clutch and have someone else turn the system on. Do this, turn the ignition off, turn the a/c system off, start engine, watch the clutch very closly and have someone else turn the a/c on. If you don't see anything happen then return to your trouble shooting. If you see the clutch enguage for just a split second, then the clutch is slipping, the speed sensor is defective, the tach signal from the engine is bad or the a/c relay is bad.
Just a thought.
An 87 SDL got me on this one time. On it, I just sprayed brake cleaner between the a/c clutch pully and disk both with the engine turned off and with the engine running but the a/c off. Every thing is fine now
.

mdisav · #17 01-10-2007, 10:50 AM

I just need to know where the compressor gets it ground from? Anybody know? Is it also from the klima like the 12v signal?

zill · #18 01-10-2007, 03:39 PM

The A/C compressor will not kick on given an outside temp of less than 32°F, correct.

It has not been that cold on the East coast though

mdisav · #19 01-10-2007, 05:37 PM

Anyone have the wiring schematics so I know how the compressor gets it's ground? Thanks!!

Hit Man X · #20 01-10-2007, 06:13 PM

Email me for the PDF for the climate.

mdisav · #21 01-11-2007, 11:29 PM

Thanks Hit Man! The PDF is helping a lot. I just lost ground to the wire that goes to the low pressure switch??? I am trying to understand the wiring schematic to see how to get that ground back.

Anyone know off hand why I would lose the ground at the pressure switch?

leathermang · #22 01-11-2007, 11:45 PM

Quote:

Originally Posted by zill

The A/C compressor will not kick on given an outside temp of less than 32°F, correct.

In defrost mode it will not kick on to evacuate moisture in the car produced by passengers if the outside temperature is less than 32 degree F ?
Does it say that somewhere in the printed literature for the car ?

mdisav · #23 01-12-2007, 08:11 AM

It has not gone below 34F here. When I bridge terminal 5 and 7 I get 12v at the compressor but nothing at the other 2 plugs at the compressor.

The clutch spins freely.

pmckechnie · #24 01-12-2007, 09:26 AM

First, the 3 wires going to the compressor are:
Blue/Green = power to compressor clutch
Red/blue and White/blue = A/C compressor speed sensor.

The only voltage you will see on the Red/Blue and White/Blue wires will be a small AC voltage IF the clutch is enguaged and compressor is turning.

If you jump pin 5 to pin 7 and the clutch doesn't enguage then the clutch coil is open or the small (usually black or brown) wire that also comes from the clutch coil is broken or disconnedted. I don't have a 300D here to look at right now but if you look carefully you should see it. It is usually connedted to the compressor itself or possibly one if the brackets.

PS I noticed in your sig that you have an 87 300D and an 84 300D but the 87 300D says (SOLD) Are we really working on an 87 300D? When working on the electrical system, the year if verrrry important.

mdisav · #25 01-12-2007, 09:54 AM

I recently acquired a 87 300TD so we are definately working on a W124. So I must have a broken wire or how does the coil to the clutch become open and how do I repair that?

mdisav · #26 01-12-2007, 12:22 PM

I found the two wires that go down the front of the compressor behind the pulley totally severed. What are these two for??

The battery was low and I got the ground back at the pressure switch after jumping the car.

mdisav · #27 01-12-2007, 12:29 PM

Also the wire coming off the back of the compressor is for what???

pmckechnie · #28 01-12-2007, 12:31 PM

The coils just go bad from 20 years of being energized,bumped, etc. The fix if that is the problem is to replace it. It is located unside the pully and can't be seen without disassembly. I see them go bad alot on all brands of cars. I don't have my 300D with me today and my 84 500SEL has a different compressor and electrical system. I will try to look tonignt or tomorrow and see where the ground wire comes out and where it is fastened.
The problem could also be the clutch itself not engaging due to wear.
Tell me what kind of test equipment you have to work with and I'll try to give you some hints for trouble shooting.

mdisav · #29 01-12-2007, 01:04 PM

I have a test light and voltmeter/ohm meter. The clutch does spin freely and I have ground at the #10 pin for the Klima and ground at the pressure switch. I also have 12v at #5 pin and power goes all the way to the compressor when jumping to #7 pin. So I believe everything is functional except the compressor.

I will take the pulley off and see where those two wires go. Thanks.

pmckechnie · #30 01-12-2007, 03:46 PM

First use the test light as the jumper. In other words, using some kind of small wire like a paper clip hook the clip of your test light to pin 5 and probe pin 7. If the test light lights, the circuit is good and you may have a mechanical problem. If the test light doesn't light then either the coil is bad or the ground wire for the coil is broken or disconnected.