I drove from Iowa to Michigan and back last week with the heat on high and the fan on low. Temp setting was 22. I have a new monovalve and checked the temp sensor in the water outlet. Got a used pushbutton unit yesterday and tried it. No change. Put the original back in and reseated the connector at the water neck and behind the RF headlight. It worked halfway home from the gas station where I work part time and then went back to blowing hot air. Is the temp sensor behind the radio the next thing to troubleshoot? I resoldered the board in the used unit last night after I got home. Should I try it again? Bad wire somewhere? I also checked a bungh of pins, 2, 4, 7 and 10 I think, against pin 12 of the right connector per the Mitchell guide. I'm stumped and have to make the trip again tomorrow. It's no fun trying to regulate temperature with the sunroof.

420 SEL heat
 

Forget my last post. I found a similar one from Feb. 200 that solved my problem. http://www.peachparts.com/shopforum/tech-help/6418-420-sel-hot-hotter.html
The water valve had just been replaced in the car so I went looking for the aux water pump. When I looked down past the new valve, I saw the plug and contacts for the new valve, separate. The mechanic had forgotten to plug in the new valve and it duplicated the symptoms of the old, stuck valve. Guess I'd better do this stuff myself instead of trusting a professional.