Suddenly! No A/C!!! - PeachParts Mercedes-Benz Forum

dwayneb · #1 05-31-2007, 05:44 PM

The A/C in my 85 190D just stopped cooling. It has been working with cold air since I bought it. The compressor kept cycling on and off, but seemed to be normal. Today, I turned on the A/C and nothing but hot air. The compressor is running and when I look in the site glass, I see bubbles so I know there is still some gas. When I press the A/C button on the ACC panel, the compressor turns on and off. When I turn it on and off, I hear a small "thunk" in the dash which I assume is some control valve or other. There is absolutely no difference in the temp of the air coming from the vents. If I thumb the temp wheel, up or down, there is no apparent difference, except that once today, when I had the temp wheel to max and pressed the A/C button, the compressor did not come on until I moved the temp wheel off max. It is still using R 12.

Oh, the compressor does not cycle on and off now, regardless of the rpm. Everything else on the car seems to be working normally.

HELP!!!

dwayneb · #2 06-01-2007, 08:06 AM

Somebody, HELP!

Brian Carlton · #3 06-01-2007, 08:17 AM

I'd like to help you, but, I don't have any schematics of that vehicle.

The typical problem occurs at the Klima relay where it fails to get all the signals required to close the compressor contacts. It might fail to get a signal from the CCU, fail to get a proper speed reference from the tach, or fail to get a proper speed reference from the compressor itself. If any of these items are outside of parameters, the Klima drops the compressor offline.

There are specific tests to find the problem, but, you'll need the FSM for that vehicle to be sure of the test socket contact points.

TX76513 · #4 06-01-2007, 08:18 AM

There is not a "do this" one line anyone can tell you from your first description of the problem. Have you checked fuse? I believe you have two temp relays on the 190 if either fails the compressor will not engage. You said - Hot air from vents - do you mean heated or just warm air circulating.

dwayneb · #5 06-01-2007, 08:54 AM

Friday morning, it's cool outside. I just went out and drove the car until the engine warmed up. The compressor DOES turn on and off. The warm air I was getting yesterday was just outside air. This morning I found out that I don't get cold air from the A/C or hot air from the heater. Repeat, my compressor does turn on and off. Does this sound like the ACC head and will the ACC head from a 93 190E work on my 85 190D. I have one. The buttons on the ACC do redirect the air and the temp wheel does cause the compressor to turn on and off but there is NO difference in temp of air. If I turn the fan on high, I can get just a very little warm air from the floor heater vent.

Thanks for ya'lls assistance.

tobybul · #6 06-01-2007, 09:25 AM

If this car has a monovalve, then I would say you have a torn diaphram.

SD Blue · #7 06-01-2007, 10:48 AM

Quote:

Originally Posted by dwayneb

Friday morning, it's cool outside. I just went out and drove the car until the engine warmed up. The compressor DOES turn on and off. The warm air I was getting yesterday was just outside air. This morning I found out that I don't get cold air from the A/C or hot air from the heater. Repeat, my compressor does turn on and off. Does this sound like the ACC head and will the ACC head from a 93 190E work on my 85 190D. I have one. The buttons on the ACC do redirect the air and the temp wheel does cause the compressor to turn on and off but there is NO difference in temp of air. If I turn the fan on high, I can get just a very little warm air from the floor heater vent.

Thanks for ya'lls assistance.

This is starting to sound like a vacuum pod/switch problem. On preceding years, all I have to go by, MB has a fresh/recirc door and a diverter door to cause air to flow over the evaporator coils. Since I don't have a schematic, not much help.

(MBUSA, has service CD's available in their classic section) (http://www.mbusa.com/heritage/index.do select "classic center" & "tech literature")

Mustang_man298 · #8 06-01-2007, 11:44 AM

If you get no heated or cooled air, and your compressor still operates, your A/C system itself is likely fine, it sounds more like a control issue, either as mentioned with the vac pods, or in the electrical controls. if you have the auto klima system, those controllers are known to go, often checking the solder joints in it helps folks.