A/C Question On W124 - PeachParts Mercedes-Benz Forum

#1 06-04-2002, 03:39 AM

My 1992 300E w/164,000 miles is a great car, But i just have one problem. When the A/C is on it blows sorta cool air in the center vents on low and hot air on the outside vents. On high it just blows hot air so i drive around on the low setting. I was thinking about getting a rebuilt climate control push button assembly as my friend advised me. Can anyone PLEASE give my some good advice. Thanks

ctaylor738 · #2 06-04-2002, 07:35 AM

Dunno about good, but here is some advice -

There are a variety of diaphragms and vacuum servos that are activated when you push the different buttons on the controls. These cause the flaps to move to the appropriate positions for heat, cool, floor, dash, etc. It is fairly common for one of these components to go south with age.

I would advise taking the car to shop that works on these cars a lot for a diagnosis before putting money into replacing a possibly good control unit.

mbdoc · #3 06-04-2002, 08:11 AM

If you ask for A/C & the center vents are cold but the outer vents are warm then most likely the heater valve isn't shutting the water OFF.

jcyuhn · #4 06-04-2002, 10:09 AM

I think you have two distinct problems here. I agree with the good MBDOC that you have a mono-valve problem. The mono-valve controls the admission of hot water into the heater. They're known to fail, in which case you get heat all the time, whether you want it or not. The good news is a repair kit is ~$25 bucks and installation is about as easy as it gets. BTW, only the outside vents are heated - it's not possible to get warmed air out of the center vents.

However, your a/c also sounds as if it is weak - probably very low on freon. The a/c system of a car can remove heat from the air at a certain, relatively fixed, rate. If you pass a little air through the system, that air is cooled down quite a bit. Pass a large volume of air through the system - by running the fan on high - and the air is cooled only a few degrees. In either case the same number of BTUs are removed. Anyways, you should have the a/c system diagnosed by a good shop. Have them check for leaks and top up the system.

#5 06-16-2002, 04:38 AM

I ordered a mono/heater valve from fastlane for about $80 and installed it. Crossed my fingers and Wah Bam!! We have Cold A/C. Park Place Motors In Houston, Tx. gave me an estimate of $4200.00. They said i needed to change out the evaporator core, vacuum and refill system, and labor. Ouch!

Did it myself with the help of this MB Forum. Total cost was about $100 to put freon in and a mono valve. What A Great Day!! Thanks Guys!

#6 06-16-2002, 10:13 AM

Chuck has been there, done that! He offers good advice.

BTW the monovalve on the 124 car is not repairable. It is the monovalve on the late 124 ACC cars that is easily repaired with the inexpensive kit.

Good luck,

bluerhino · #7 06-16-2002, 10:30 AM

What's the part number for this mono-valve for 124. How are they called at fastlane?

Amuso · #8 06-17-2002, 10:31 AM

Is this an electrically operated valve? I saw a "device" in front of my battery on the passenger side in my W124. Is this the mono-valve?

#9 06-17-2002, 11:04 AM

On my 1992 300 E the Part# was R3022-36289 - ACC Mono Valve. Yep, it's that electrical valve thing with 3 coolant hoses attached to it next to the battery. Hope that helps you.

Amuso · #10 06-17-2002, 11:11 AM

Ah thanks! Yeah, I did test mine during the weekend. Applied power and made a hearable click. My klima relay is blown so that explains why my car has been throwing semi-hot air while driving. I guess that valve was stuck open and let the engine water flow through the coupe.