Quirky Climate Control - PeachParts Mercedes-Benz Forum

tgh93 · #1 11-02-2003, 03:55 PM

I just started using the heater and it heats the car up and you are comfortable. Then after aout 15 minutes it decides to blow full heat. I roll the setting back and get the ac on to cool it down. then After another 15 minutes we do this again. I replaced the push button unit about 2 years ago. By the way it is a 1982 300TD. Thanks

#2 11-02-2003, 05:39 PM

Possible MONO VALVE or deteriorated FOAM HOSE connector behind the glove box causing the on top of dash sensor to read incorrectly. Change both and corrected my heating problems. See this thread:
[URL=http://www.peachparts.com/shopforum/showthread.php?s=&threadid=78365[/URL]

#3 11-02-2003, 05:41 PM

Automatic Climate Control – Sign of Fatique?

tgh93 · #4 11-02-2003, 06:28 PM

I'll check the hose first. Where is the monovalve located?

#5 11-03-2003, 12:09 AM

Quote:

Originally posted by tgh93
I'll check the hose first. Where is the monovalve located?

On the firewall next to the battery and above the atf dipstick.

tgh93 · #6 11-03-2003, 06:50 AM

Thank you. I really appreciate the help.

tgh93 · #7 11-03-2003, 06:19 PM

I changed the hose this morning. It seemed to help a little but it still will go to full heat and not shut down unless I roll the wheel to cool. I usually have it set on 22 but when it keeps blowing hot I go to 18. Next I guess will be the monovalve.

84300DT · #8 11-03-2003, 08:05 PM

check the cabin temp sensor at the center of the dash.

lrg · #9 11-04-2003, 12:29 PM

If you are getting full heat and able to regulate to cold then it is probably NOT the monovalve. I agree that it may be the temp sensor or sampling motor that draws air past the sensor. They are accessable by removing the interior of the glovebox and the passenger side kick panel. While it is unlikely that your two year old CCU is bad be aware that a shorted coolant circulation pump has been known to ruin the CCU. It's best to double check that the circulation pump is still running too. If you you put your hand on the motor with the heat set to hot and the engine warm and idling you should be able to feel it running.

tgh93 · #10 11-04-2003, 05:17 PM

I checked the monovalve and it looked fine. Where is the circulation pump located? Thanks Eroc

lrg · #11 11-04-2003, 06:42 PM

It varies depending upon the year/model but it should be easy to find by following the heater hoses in the engine compartment. On my '85 California wagon I believe it's up front near the air cleaner. It's a bit smaller than your fist and has a black plastic pump body. It's designed to keep the hot water circulating at lower RPM so you still get all the heat you want when the engine is idling. The problem is that if the pump shorts out it tends to pull more current through the CCU circuit board than the CCU can handle so it ends up frying the CCU. I still think the temp sensor and/or sampling motor are the most likely suspects for your problem but it's a good idea to check the circulation pump anyway.

tgh93 · #12 11-05-2003, 06:09 PM

I checked the circulation pump and it seemed ok. What does the temp sensor look like. Thanks

lrg · #13 11-05-2003, 06:21 PM

It's a small diode like device that is under the little square grille in the center of your dash (attached to the end of the hose you just repaired). You may be able to get at it from above (I've never tried) but my guess is it is best accessed from behind the glove box as you'll want to check the wires that are attached to it. The sampling motor produces a suction that draws cabin air in that little grill and across the sensor. A bad connection there or faulty senor might cause symptoms like yours. It is possible to test it according to the shop manual.

tgh93 · #14 11-07-2003, 09:23 PM

I put a kleenex over theinlet for the sampling and it would pull it down (not alot of pressure), I guess thats enough? Is there a way to test the ambient sensor and if it is bad where can one get one? Thanks

samiam4 · #15 11-08-2003, 01:05 PM

What's the test for the sensor???

This symptom is exactly like mine. I don't think my coolant pump is running. I can feel a difference in idle heating vs cruiz.

I've been lazy and not checked the foam tube piece yet-