Hi! Thanks so much for your post! That is incredible information! I have a few further questions if you don't mind.

I bet you are right about the problem we are having. I suspect that it's 38. I will have to test 40 to see if it works. The question is: How do I find the connector for 40? I noticed that there is a connector on the front of the heater box, but I think there is another connector below the box too. From what you say, I think the front connector (red & yellow) must control the heater vents, so the connector for 40 must be somewhere else on the box.

We noticed that there is vacuum but I am not sure how much there should be, and it's possible that some is leaking somewhere.

Also noteworthy: the front of the heater box, visible from where the ac controls and radio are, was cracked and a small piece (the piece with the rivets) was completely broken out, and it would move up and down when we changed modes on the climate control. When we found out how much it costs to replace a heater box, we repaired it by pulling the broken bit, which had gone inside the heater box a fourth of an inch or so, back out as far as possible, and then sealing it in with a healthy dose of epoxy. Now, it's pretty secure, but it is not completely flush -- it is actually about 1/8 of an inch inside the heater box, as that was as far as we could pull it out.

Thanks again, and we really appreciate you helping out.