Automatic Climate Control – Sign of Fatique? - PeachParts Mercedes-Benz Forum

#1 10-30-2003, 12:04 AM

The A/C (retrofitted to R134a) was nice and cold all summer. Now it’s fall and heat is preferred. Ambient temp: about 62*F. With Smokeless running at normal operating temp (85*-90*C); ACC temp dial set at 22*C; EC button pushed in; Fan speed on AUTO warm air blowing on the side vents fine.

Later on, without any setting change, warm air changed to lukewarm air. Turning temp dial to MAX, no changed. Hmmm. I don’t recall the sequence of button-pushing and temp dial turning but somehow I managed to reset the ACC to the above condition.

Something is failing, what may it be?

fahrgewehr2 · #2 10-30-2003, 12:28 AM

I can't answer your question, but the same thing happened to me tonight.

On my drive home, air from vents became luke warm, and finally, cold (same as outside temp).

I parked the car and started her back up and heat blew as it should. shut it back down.

Will see what develops tomorrow. Good luck to both of us.

Mike

mercedesmatt · #3 10-30-2003, 12:35 AM

check your mono valve diaphrams first, then you may wanna look at the temp amp behind the glove box.

lrg · #4 10-30-2003, 01:19 AM

99% probability it's the monovalve. Often when they fail you won't get enough heat except at low fan speeds. It's pretty easy to check. Remove the top of the valve body and withdraw the cartridge. If you see any cracks on the rubber in the middle of the cartridge it needs to be replaced. Fortunately a replacemnet cartridge is not expensive and it's an easy job (except on the late California cars that have a heat shield that gets in the way).

fahrgewehr2 · #5 10-30-2003, 01:31 AM

I'm in route to the garage...thanks!

Mike

#6 10-30-2003, 03:02 AM

After a forum search on "Mono Valve" and read plenty of threads on the subject, it appears that my problem points to a faulty Mono Valve. I will be get a hold of a DIY Repair Kit and see what happens.

Question: When the ACC Defrost button is pressed and the fan goes to high speed, is it normal that you get hot air (this is what mine does) blowing out the vents? I always thought that the Defrost button will turn on the a/c compressor and hence dry cool air should blow out?

engatwork · #7 10-30-2003, 06:34 AM

Defroast button pressed = hot air full blast out of the defroast section and side vents if I remember correctly.

fahrgewehr2 · #8 10-30-2003, 07:22 PM

I jsut changed out my monovlavle diaphram. Will get back to you if it works.

Mike

#9 10-30-2003, 09:55 PM

This Forum is great!!!

NO HEAT at high speed but HEAT at idle speed, purchased and installed Bosch Mono Valve Repair Kit (1 147 213 007) C$45.80 (Oct 2003) and everything works fine now.

This forum suggests that if NO HEAT at idle speed, could be Auxilliary Water Pump.

fahrgewehr2 · #10 10-31-2003, 12:56 AM

I have heat again too! Whoo Hoo!

For the sake of the archives- job not very hard and took a ham fisted oaf like myself less than one hour.

Mike

Ken300D · #11 10-31-2003, 06:56 AM

I have something of the opposite problem with the 82 300D. The system will start providing heat but seems to get stuck on full heat.

In the past I have found the air tube behind the glove box was disintegrated, and replaced it. The symptom of that problem is that you have to keep bumping up the temperature wheel a little bit to maintain a comfortable temperature. This is because the temperature in the dash gets warmer faster and stays warmer than the regular passenger compartment. So, when the air sensor tube is gone the system pulls air to sense from within the dash.

However, my ACC seems to vary between good temperature regulation and FULL HEAT.

Would this be more of a controller problem, or could the monovalve possibly stick OPEN?

Ken300D

fahrgewehr2 · #12 10-31-2003, 11:14 AM

Ken-

When I purchased the part from my mechanic, he told me that your symptom could also be a sign of a faulty monovalve. I would just swap out the insert and hope for the best, since the part is cheap and its easy to do.

I looked on fast lane and the "repair kit" for your car is the same as mine, same price too ($34).

Mike

#13 10-31-2003, 11:33 PM

Quote:

Originally posted by Ken300D
... In the past I have found the air tube behind the glove box was disintegrated, and replaced it....Ken300D

Foam Air Tube Replacement

I am not sure what MB engineers were thinking to have decided to use a foam hose to join two plastic air tubes. However, replacing the hose is very easy and simple: a) removal of passenger side under dash cover; b) removal of glove box; c) removal of old disintegrated foam hose.

Foam pipe insulation is what I used to replace it. ACC heat sensor (on the dash) is now working fine.

See picture 1 of 4

#14 10-31-2003, 11:34 PM

Pcture 2 of 4

#15 10-31-2003, 11:35 PM

Picture 3 of 4