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H-townbenzoboy 11-05-2004 12:15 PM

1982 300D A/C and heat won't work right!!!
Okay, it's cool in Houston now, but when we had temps in the 80's and 90's just a week ago, I could only set the A/C to MIN temp setting to have cold air, any other setting that was not MIN would blow hot air. Now, I can't get heat in the cool mornings. Cold air blows out!!! Even on MAX temp!!! What's wrong here?

benzzy 11-05-2004 01:03 PM

Sounds like a mono valuve issue to me...
I had to rebuild mine this year...had a similair problem.

I bought one from Phil, and it took about ten minute to install.

At anyrate when your using your multimeter to check your glow plug set up check out the mono valve too on the fire wall.

sixto 11-07-2004 01:19 AM

Other consideration - check that the aspirator motor is drawing air over the cabin temp sensor (there's either a small opening in the middle of the dash or by the front dome light), and that the cabin temp sensor is working.

95 S420
87 300SDL

LarryBible 11-07-2004 10:44 AM

On the 123 there is no aspirator motor.

Pull the glove box and look to the left and forward of the glove box for a plastic pipe running horizontal. There should be a foam hose running across to the temp sensor that is under the little grill in the center top of the dash.

It is probably dissintegrated and gone. Go to Home Depot and get a stick of foam pipe insulation and cut a length to slip over these two connections. Don't use any other type of hose except foam due to the thermal properties of the foam.

Good luck,

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