89CE

Hi all. Well I just picked up a very clean 92 2.6. The problem is that the a/c compressor is not engaging, hence no cold air blowing. Does this year have a relay? What other possible causes would be suspect? Any advice is welcomed.
Thanks in advance!

Jer

There are several things to check:

-The "Klima" control unit disengages the compressor if it labors or if the comp. speed and engine speed are not in agreement. Sometimes these go bad and need to be replaced. It can be found on the passenger side in the engine compartment behind a plastic cover (at least on the W124).

-The pushbutton control unit (auto climate controls) might be defective. You can get a rebuilt one with a core refund for sending in the old one.

89CE

On the 1992 190E 2.6, there are no "KLIMA" and "KICKDOWN"
relays in the back of the plastic cover, like the ones found in W124s. What I have back there are the voltage protector (the one with the fuse on top), and a large relay looking part that has "MAS" on written on it. Anyone know where I can find the compressor relay, or is it the "MAS"?

MTI

On the 2.6L the A/C compressor relay is located on the battery side of the engine bay. It's in the same grouping as the MAS Control Unit and the OVP (the one with the fuse on top) relay. The A/C compressor relay should be right in back of the MAS Control unit and to the left of the CIS Control Unit.

89CE

There's nothing in back of the MAS unit because it's mounted on the firewall itself. The OVP is in front of the MAS, and the CIS computers are to the right of the MAS. I cant find the compressor relay and the fuel pump relay. This car has to have these relays right? I took a pic of the area where the relays are located.
Any help is appreciated. Thanks.

bamberger_1

Could it be this is a later added aftermarket A/C? These normally having the function hard wired some where with normal car relays. My guess in your case is, that your system needs recharge of refrigerant. Since if the refrigerant is low the compressor is protected by a pressure switch. If there is no larger leak, rather than you lost the R134a slowly over time (3-4 years) just have it recharged.

germantoys12345

1993 190e 2.3 compressor clutch will not engage. use to work, can,t charge as compressor won,t engage, how to check the clutch for continuity and ohms

190Efan

Do you hear any noise at all from the compressor? I'm wondering if the compressor clutch isn't engaging because the compressor itself isn't working? You also need to check if your A/C is still the R 12 or if it's been converted to the R134A.If it's still R12, the freon is pretty much not available any more.

lsmalley

Unplug the compressor and just run 12v to the clutch with the engine off to see if it engages. Clutch pin is the one closest to the top where the blue/green wire connects. At least I believe, it's blue and green, the 2 that go to the speed sensor are the one in the middle which is white/blue, and the one at the very bottom which is red and white. At any rate, which ever the color of the clutch wire is, it's definitely the top pin. I've pretty much dissected my entire system for my w201 ac and I have had zero issues with it. If the clutch does engage, then there are a few things that prevent it from turning on:
1) refrigerant pressure sensor
2) evap temp sensor
3) coolant temp sensor
4) speed/rpm sensor on the compressor
5) engine speed sensor
6) serpentine belt loose
7) interruption or short circuit from the push button climate control
8) low/no refrigerant
9) in cabin temp sensor
It doesn't matter what refrigerant you have in your system (I use r152a) if any of the above numbered conditions are faulty your ac won't work.

190Efan

That's not entirely true. You need to have the rest of your A/C system parts updated to be able to use the newer refrigerants. You can't just start using the newer refrigerants in a system that was only designed for R12.

lsmalley

The only thing that you would need is to change out is the service port because R12 is different from R134 and also the o-rings and oil flush....but I wasn't disputing any of that, what I was saying is that if any of the several items I listed are faulty, then the ac would not work, period, regardless of what refrigerant was ran through the system.

190Efan

While I agree that any of the other items you listed could cause the A/C to not work, your continuing claim that only minimal changes are needed to be able to run R134 in a car designed to run R12 is not accurate.

lsmalley

I personally did my own conversion from R12 on my AC to R134, before I switched to R152. I did the following: Evacuated what little R12 was left in the system, removed the receiver drier and installed another one, then I flushed the system over a period of 2 days with Liqui Moly AC flush to remove the oil. I then removed the compressor and replaced it with a new one (same model), I then removed the receiver drier and put in a new one and of course replaced the o-rings. The only part of my ac system that is not exactly the same as when it came off the line is the oil and refrigerant and the new r134 quick connect port I installed, other than that everything is the same. Please explain why you believe that converting from r12 to r134 is some huge elaborate process. And yes, I still have the r152 and I can easily get temps in the 30 degree range from the vents with the ambient socal desert temp being 110+ degrees.

190Efan

It's my understanding based on numerous people who've made the conversion from R12 to R134 that you need to replace pretty much every thing in the A/C system. I hope your conversion continues to work for you.

Deadbolt9009

Good explanation of how to test Compressor Clutch. I also have a W201 2.6 (1991with 233,000 miles). I recently had the Air Pump Clutch Bearing seize up which caused complete destruction of the serpentine belt. I have since replaced the Air Pump, Idler Pulley, Belt Tensioner (OEM Febi), Tensioner adjusting bolt/nut (OEM) as well as the belt and everything is working great except for the A/C. The clutch will not engage. I’ve put pressure gauge on low side of A/C and can not get a good read. Is this because the Compressor Clutch will not engage? Before the air pump problems, my A/C system was working well. Would appreciate any help/info/ you can provide. Thanks!.

lsmalley

Disconnect the compressor plug and run +12v to the pin to see if the clutch engages. If it does, run the engine with the +12v to the clutch and check your pressures. While you are checking your pressures, make sure your fans turn on. Go into the cabin and verify that you are getting cold air. This will establish that the compressor works and there is a charge in the system. Report back with your findings

lsmalley

Ended up finding this bulletin from MB. Anyone that is still running the outdated R12 and wishes to update their AC system, here is the info. Though, you don't necessarily need to use R134a, which is also outdated, you can choose to run any compatible refrigerant of your choice. As mentioned before, I currently use the R152a, which is readily available at any office supply store, Wal-Mart, general store, or online. I've previously used the R134a, which was way to expensive and time consuming, due to not being able to just vent it out when making any minor repair like changing a sensor or even replacing a part of the AC system. I also tried the R290/R600 propane/isobutane, which was surprisingly really cold, but it made me a little nervous tbh. Anyways, now that the hot weather is coming to an end, now would be a good time to considering doing this if you want, since you would be in no urgent rush or need to use your AC.