More monovalve questions for 87 300D
 

I think I have this issue under control, but just wanted to doublecheck I'm taking the right course of action. My monovalve has entirely quit at this point, in that I get 12v to it but still have constant heat. I tried supplying 12v to the pins myself and get no sound. I have a spare used monovalve on my shelf, I think also from am 87 300D, and when I put 12v to that, I get a substantial click. Can I assume that the coil in my monovalve is kaput? So the whole unit needs to be replaced? Or is the lack of any noise possibly due to the valve being stuck ... in which case I could rebuild it I suppose (I noticed via a search that a lot of people rebuilt them).
In either case, is there any reason not to use the used one I have? It seems to work electronically and I thought I could just swap it in and see if it works.

You can go a step further and put an ohm meter across the leads on the "dead" one and verify that it has an open circuit to the coil.

It may be possible to take it apart and find the break in the wire and solder (your favorite thing) it back together. Bring it to Chads and we can have a look. I need some more stuff to fill up the day... :)

Well, all my soldering equipment is still in a pile on the floor from the last project, so I might as well use it again before I put it away.;) Do you think it'd be OK to use the spare used one while I fiddle with the other? Even with the break in the weather, the constant blazing heat trickling out of my vents is a bit oppressive.

It can't hurt to swap it out and then try to repair the one from the car. Then, you can keep that one for a spare if you manage to fix it.

Before swapping in the used mono valve, applied 12 volts then pour some water into it to test for a torn diaphragm.

Good idea! It holds the water with 12v supplied. Will swap it in today. :)

New-used monovalve installed ... I think it's working now, though I will have to try a test drive. I got it up to operating temp in the driveway and the air coming out is not blazing hot like it was before (though it's still warm, probably because it's warm out ... no A/C in this car).
Stupid question: Is it normal that the metal cylindrical part of the housing gets a bit hot (not too hot to touch, just toasty), even before the coolant got hot? Is that just heat from the electrical current? As usual, I'm nervous it's just going to burst into flames.

The coil indeed gets hot if it's energized (when turning off the heat). When supplying full heat to the car it gets hot from the hot coolant ("hottant?").

Jeremy