Too Much Heat - PeachParts Mercedes-Benz Forum

kchemers · #1 11-13-2009, 11:34 PM

89 300TE
1.When car is cold and climate control is set to auto, blower comes on immediately, blower in the past would not kick on until engine was at operating temp
2.heat will blow out of floor vents for awhile then they close and heat comes out the dash vents
3.doesnt matter what the thermostat is set at, heat will continue to get hotter
even if I set thermostat all the way down to max cool
4. can hear doors trying to open or close from behind glove box, not sure what they are trying to do
5.heat extremely hot out of side dash vents, both sides
6. defrost setting works
7. low fan will stilll blow extremely hot air, only relief the in the cabin is to shut system down
8.too cold out now to get a/c to work
9. no idea of what to do, or where to start
10. PLEASE HELP !
Thanks kchemers

kchemers · #2 11-14-2009, 05:03 PM

11. today was 65 and the compressor refused to kick on, blowing hot air from dash vents

kchemers · #3 11-15-2009, 12:06 PM

Someone has to be familiar with this!
Ken

ds190 · #4 11-15-2009, 06:29 PM

The first step is to check that the ventilation blower is working. It is a small blower motor tucked in the dash board under the right vent that always runs whenever the ignition is on. Always.

Cut a piece of paper 1cm x 1cm, turn ignition on (doesn't matter what button is pushed in on climate control unit), and hold paper up to temp sensor grill near overhead light. It should stay up there.

If it falls off, ventilation blower is not blowing, and not pulling air past the temperature sensor up in the overhead light assembly. The CCU doesn't get accurate info of how hot the interior is, so blows full blast. It never slows down.

I've had this problem in two 124 cars. Other people have reported that the foam hose from the temp sensor to the vent blower has disintegrated.

It's something to start with.

kchemers · #5 11-16-2009, 03:43 PM

Thank you I will try that today!
Ken

tinypanzer · #6 11-16-2009, 06:32 PM

Other possibility is a blasted open monovalve diaphragm, or a bad engine coolant temp sensor. The fact that the fan comes on right away would indicate the CCU thinks the coolant is hotter than it is.

Could also be a CCU problem, but I would start checking both interior and coolant temp sensors, and verifying the monovalve is OK.

dhjenkins · #7 11-16-2009, 06:56 PM

Sounds like a bad monovalve. I know when I was messing around with my climate control and disconnected the monovalve connector, all I could get out of the vents was hot air.

kchemers · #8 11-17-2009, 08:45 AM

Thank you , I will try all the suggestions

gmercoleza · #9 11-17-2009, 09:30 AM

My 560SEL did this - Monovalve was shot and was stuck open. Try using clamps or vice-grips to block the hoses going to the monovalve. If the heat stops, your monovalve is bad.

kchemers · #10 12-05-2009, 09:03 PM

Finally had time to hit the junk yard, picked up a monovalve and now have complete control of the heating and cooling system. Once again this forum has come to the rescue!
Thanks for the help
Ken

Camohall · #11 12-07-2009, 02:03 PM

What about the reverse? Could it be the monovalve that is going bad when there's no heat at all?

ps2cho · #12 12-07-2009, 06:13 PM

Thank you for replying with the outcome! Good to know for future reference.

tinypanzer · #13 12-07-2009, 07:43 PM

Quote:

Originally Posted by Camohall

What about the reverse? Could it be the monovalve that is going bad when there's no heat at all?

Yes it could. When that diaphragm tears, it can present either symptom. A small tear seems to make it not want to open due to fluid getting behind the diaphragm while a large tear just lets the coolant rush past.

Another possibility is the coil, but if the coil was blown (open), you would get heat constantly.

Frankly, I'm surprised I haven't seen more bad coils. They are often wet with coolant when you pull them out, which makes me wonder why I have yet to see one that is burned up.....