Heater trouble

[krwsenior]

The heater comes on and goes off whenever it so desires on my 83 300D Turbo. The A/C will be working fine, then all of a sudden, the heat takes over and overwhelms it.

Any ideas why this may be happening? Changing the settings does nothing to cut it off. The heat comes on and goes off at random it seems.

Thanks, KRW

[Cr from Texas]

I've had the same kind of issues over the years. When I'm lucky it's been the heater control valve. When I'm not lucky its been the CCU.

Check the electrical connection on the top of the monovalve, if it's loose the heat will come on intermittently. I recently fixed that problem by putting some conductive "grease" on that connector.

[krwsenior]

Thanks! I will try the grease on the elec connector first. Hopefully that will take care of it. My wife will be pleased. It's getting hot these days in Louisiana. KRW

Hopefully, you will be lucky and that will be the issue. It seems likely because you heat is random. If the heat tends to come on at high speeds only, I would suspect that the monovalve needs to be rebuilt.

[krwsenior]

I rebuilt the monovalve a little less than a year ago. I wouldn't think it would go out so soon. I just put some grease on the electrical connection and the air is working again. Of course, I can't tell yet if the problem will come back again.

Thanks for the tips! This site is great. KRW

Good luck, hope that's it. Let us know.

[tangofox007]

Originally Posted by Craig

If the heat tends to come on at high speeds only, I would suspect that the monovalve needs to be rebuilt.

In my experience, a monovalve diaphragm failure (tear or rupture) will cause the heat to not work at higher speeds.

Originally Posted by tangofox007

In my experience, a monovalve diaphragm failure (tear or rupture) will cause the heat to not work at higher speeds.

Yup, I'm backwards. In any event, the random heat failure sounds like a loose connection. Hopefully it's that easy.

[krwsenior]

The heater came on by itself again today. I guess the controller in the dash is bad. I thought for a while there the grease on the elec connection did the trick. KRW

[krwsenior]

I guess I should go ahead and tear into the dash and change the pods. I've been putting it off and have the vents wired open. KRW

Originally Posted by krwsenior

I guess I should go ahead and tear into the dash and change the pods. I've been putting it off and have the vents wired open. KRW

It's not the pods, the heat is controlled by the monovalve and the monovalve is controlled by the pushbutton unit and the temperature control. When the AC is on, the monovalve should be closed. The pods just direct the airflow.

[krwsenior]

Yes, I realize that the pods are not causing this problem, but it's something I need to do anyway. Maybe now is the time to fix it all at the same time.

Originally Posted by krwsenior

Yes, I realize that the pods are not causing this problem, but it's something I need to do anyway. Maybe now is the time to fix it all at the same time.

Yup, might as well get it all over with at once.

[MB-Owner-in-ind]

I had the same thing with mine and although I had just replaced the mono valve, it had gone bad again. It takes only a little time to check. You will see the rubber broke somewhere.