Part time A/C on my 124 - PeachParts Mercedes-Benz Forum

muleears · #1 04-30-2007, 06:09 PM

My ac compressor shuts off after about 5 min. It will initially cool but then the compressor stops and all I get is warm air. If the car is allowed to cool down it will work again but only for about 5 min. Through my search I have come across some possibilities:

KLIMA: my car has had the KLIMA replaced by the ice cube. I know, not a good idea on the 603 but I didn't do it. But if this were bad the AC would not work at all would it?

Temp. Switch, my guess is that a temp. switch has gone bad and is turning the compressor off too quickly. I have looked at the temp. switch at Fastlane, but don't know where it is located on my car. If I am on the right track could someone point it out to me?

The AC worked fine last week, not COLD but cool (R134A)

Now, all of a sudden its acting up

Any help is appreciated.

muleears · #2 04-30-2007, 06:48 PM

I found the temp. switch (red cap in lower left of pic) but why do the two wires from it go, one to a double connector and the other just hangs there?? I am now officially very confused. Even if the switch is bad would I rewire the new one the same way?

softconsult · #3 04-30-2007, 06:54 PM

One possibility. If you are too low on freon, the system cuts off the compressor.

Steve

Jeremy5848 · #4 05-01-2007, 12:03 AM

Quote:

Originally Posted by softconsult

One possibility. If you are too low on freon, the system cuts off the compressor.

Steve

But if the Klima relay is bypassed by the icecube relay, that safety feature does not work. Additionally, the picture looks like someone has bypassed the safety switch, not a good thing. Better check the Freon level before the compressor is damaged -- it is one expensive puppy!

TimFreeh · #5 05-01-2007, 08:55 AM

Quote:

Originally Posted by Jeremy5848

But if the Klima relay is bypassed by the icecube relay, that safety feature does not work. Additionally, the picture looks like someone has bypassed the safety switch, not a good thing. Better check the Freon level before the compressor is damaged -- it is one expensive puppy!

Not true - of course its tough to say for sure if somebody has been fooling around with the system by bypassing the function of the KLIMA relay.

The KLIMA relay will disengage the compressor when it detects 1) belt slippage 2)a wide open throttle condition (caused by the kickdown switch OR the wide-open throttle switch) or 3) coolant temperatures about 115C. If the functions of the KLIMA has been bypassed by a "dumb" relay these are the safety functions that will no longer be in play.

The red switch in your picture is a two contact 'make or break' pressure switch. A signal is passed through the both poles of the switch to the KLIMA relay (or in your case the "ice-cube" relay) from the ACC pushbutton control unit to indicate it wants compressor engagement. The KLIMA unit receives this request and determines whether or not it can actually engage the compressor based upon the parameters mentioned above.

What is really strange is that if somebody pulled the plug on the two prong pressure switch it should interrupt the engagement signal from the ACC pushutton unit and the compressor should NEVER engage.

It seems like the person that replaced the KLIMA relay may have been involved in some other "system enhancements". You are going to need a schematic diagram of the system and somebody that can figure out what was modified and how to fix it or put the system back to the way it came from the factory before you can diagnose whats wrong.

muleears · #6 05-01-2007, 12:05 PM

Thanks Tim. Today it ran for about 10 min before quitting. One other odd sympton is it has started to run the ventilation fan with the acc switch off!
When it starts blowing warm air I push the "O" on the acc and everything goes off. Then a few minutes later the fan starts on high and blows out the center vents. It has never done this before. Could the ACC or the switches be bad? Thanks again for the help.

babymog · #7 05-01-2007, 12:15 PM

Oddly enough Mule, my '87 was running in the off position also.
A/C worked great, even in econ or off mode, the compressor would sometimes run. Cycling the switches would turn it off again, but eventually the fan would start blowing, and the compressor.

I replaced the CCU with a known working one from my other car, all was well, so in went a new one and it works great.

I don't know why my CCU failed, this is why I tried the used one first (in case a short or something would take out the new unit). Seems okay though. BTW, my car is not altered from the original wiring, so it isn't necessarily your wiring that has changed the functions.

Try the CCU from Fritz.

muleears · #8 05-01-2007, 06:04 PM

Its actually Fritz thats having the problems. Loni's AC doesn't work at all. However the CCU may still be OK. I'll do a search to find where the CCU is, swap them, and hopefully that will fix my problem. Could the CCU also cause the AC problem?

babymog · #9 05-01-2007, 06:20 PM

The CCU is the pushbutton unit in the dash. Remove the two screws above the radio, swing the zebrano panel out/up, remove. Remove the six screws in the CCU and slide the unit out.

The CCU does need to call for cooling for the compressor to run, certainly can be related.

muleears · #10 05-01-2007, 07:05 PM

Well, I did the transplant, still no AC. I don't think I drove far enough to test wether it will come on by itself or not, sometimes that takes 15 min. Usually the ac works when first started, but this time not, I guess it was still hot from the 45 mile drive home. Thanks for the help, any other suggestions?

pberku · #11 05-01-2007, 10:00 PM

If you look closely at the the two wires going away from the high pressure switch (The ones with the female connector) I am sure that you will note that they have been jumped together. If that's the case, then that's what allows your compressor to come on even though one of the wires coming from your red switch is not plugged in. In other words, someone bypassed the red high pressure limit switch.

By the way, The red AC switch is a high pressure AC switch, not a temperature switch.

jbach36 · #12 05-01-2007, 10:45 PM

Laugh as you may, but a seemingly fine serpentine belt (on my W124) was causing the a/c to not work. Also if you don't have a splash guard (aka belly pan) under the car, water can get up on the belt and electrical components. It's a very important piece to the car.

Jeff 1991 300d

muleears · #13 05-02-2007, 06:04 AM

The belt has about 10K on it, haven't noticed any squealing. No the car does not have the belly pan anymore. It hasn't rained in several days so it shouldn't be wet.

I have another problem, probably related, now a relay behind/around the glove box keeps clicking on and off whenever the ventilation is on. It will do this several times a minute. Once the ventilation is turned off it stops clicking. Could I be hearing the "ice cube" clicking? What I hear sounds like it is inside the car though.

I will swap the CCU's back this evening as the "newest" one apparently doesn't work as it turns the fan on and off frequently if the ventilation is on, but not in unison with the clicking relay. It didn't turn the fan on once turned off though. I'll pull the glovebox tonite to see if the relay will click while sitting in the driveway and see if I can find it behind the dash.

Thanks for the help so far, I think we are making progress.

babymog · #14 05-02-2007, 09:04 AM

I think I'd unplug the aux pump, it's under the washer bottle, in case it's drawing too much and causing the problem.

The thing clicking under the glovebox is the vacuum-controller relay array, not sure what it's called, controlled by the CCU and other signals. Check the air sampling blower under the right vent while you have the glovebox out, if it's not working correctly your climate control will cycle, I'm not sure whether it'll cause additional problems if it's stalled/drawing too much.

muleears · #15 05-02-2007, 12:06 PM

Thanks babymog. I had the air sampler out for a lube about a month ago, so I think its ok. How do I check the vacuum/relay you mentioned? Should I do a transplant there also? Could that be stopping my AC compressor?