The control valve is working. When we drive the car there is no heat. When we shut the car off, wait a few seconds and turn the key on (we do not start the engine) there is heat. Once the car is started, it goes back to cool.

Response from seweavers
1 question asked

you failed to mention that the circulation pump was working. it is starting to sound like a plugged heater core, you can remove the line from a heater control valve and use your garden hose and try to blow out the heater core to see if you've got a circulation

Answered by Dr Loot (expert)
2,178 answers provided

I do not have the circulation pump as shown in the picture. this pump is on my 300d that we have but not the 300sd. I can get very hot air when the engine is off.
We are getting circulation but in my opinion it may be inadequate. I beileve ther is another type of valve under the valve at the firewall. It does NOT have any wires going to it but the hoses do. Will try to bypass this to see if flow increases.
I have an 83 and 84 sd and 1 84 300d and 2 85 300sd.

Response from seweavers
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that would change everything if it is a 300d..... I have one of those in my storage lot, let me go take a look at it and I will get back to you

Answered by Dr Loot (expert)
2,178 answers provided

This is on a 300sd. one of the photos you had posted was not like the 300sd, it was like the 300d.

Response from seweavers
1 question asked