Weird problem with heating system
Thread Starter
Junior Member
Joined: Nov 2007
Posts: 15
Likes: 3
From: Shenandoah Valley, Virginia
1990 300se, 1980 450sl
Weird problem with heating system
Before posting, I did a search and did not find the same problem.
With my 1990 300se, you can set the heat on "econo" and it seems to work fine, including when you change the temp setting up and down. Here's the problem.
When you change from the "econo" to say "defrost" it starts to blow cold air, if you go back to "econo" it blows cold air. If you turn off the car and turn it back on, it works correctly again. If you turn the car off, set it on defrost, turn the car back on, it blows hot air. like it should.
It appears by turning the car off and back on it resets something, any ideas??
Paul Waddell
1990 300se
Front Royal, VA
With my 1990 300se, you can set the heat on "econo" and it seems to work fine, including when you change the temp setting up and down. Here's the problem.
When you change from the "econo" to say "defrost" it starts to blow cold air, if you go back to "econo" it blows cold air. If you turn off the car and turn it back on, it works correctly again. If you turn the car off, set it on defrost, turn the car back on, it blows hot air. like it should.
It appears by turning the car off and back on it resets something, any ideas??
Paul Waddell
1990 300se
Front Royal, VA
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Joined: May 2006
Posts: 1,318
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From: Virginia
W212 M276 DELA 30 ; W211 M113k, W126 M117, W126 OM617, W211 OM642 ; R107 M117 X2, Sierra 1500 LZ0
Its probably your monovalve. Do a search. I found a great pictorial on how to replace it. I was able to do so in a dark garage with just a screw driver (simple fix).
