After changing out the vacuum relay, the Tempmatic worked correctly on my drive to work yesterday, however when I started it up to go home the heat never came on. When I got home and shut it off I didn't hear the spring relaxing, so once again the vacuum relay isn't working. There's two paths forward that I can see:

1.) Jury rig a check valve in place of the unreliable original design. With some fittings it should be possible to make it work with the existing vacuum lines. If this valve does the same function as the vacuum relay, then just maybe it can be used as a substitute.

2.) I found a YouTube video showing it theoretically maybe possible to convert the Tempmatic into a manual climate control. Don't know if it would work. https://youtu.be/I7aqIETsIYw?si=qxZWwxCANwr2Rfiw

 

Having put some thought into it I decided to try option 1 as it doesn't cost that much and is readily available, and best of all requires minimum modifications. Tonight I pulled the programmer out again and replaced the replacement vacuum valve with this one. I did have to get a fitting for it which allowed it to work with the original vacuum line that comes in from the engine, I believe the original is 1/8 and this new one is 1/4". The other two lines that go to the vacuum motor and compensator are both exact fits to this new check valve output so no modifications were needed. Afterwords it's just a matter of putting everything else back in and bolting it together like usual. I took it for a short 2 mile test and drive, and I pleased to report that I have heat again. Here's a picture of the setup:



Now this is a preliminary assessment as it's only been on the road a little bit, and being winter I can expect the heater to be on frequently. It remains to be seen if the heat will shut off on its own when the cabin gets warm enough. But so far this is a very encouraging sign.

 

I wasn't sure if it was shutting off on my longer commutes at the specified temp, so I grabbed a thermometer and put it inside the cabin. Turns out, it actually WORKS. I had it set to 75, and it stopped warming up at 75. While it was still on heater I raised the temp slider a little bit and heard the unit respond and it started getting warmer. I did try putting it to a cooler temp, but it wouldn't go back. I'm not sure if this is just how they are or if there's another issue. But so far it seems using this check valve, part number 15733271, is a viable fix.

 

Stickied, thanks for the good info.

 

As an update to this after fixing a vacuum leak in the vacuum motor I have come to realize it's still using too much vacuum. At first I thought there was a leak in a diaphragm, but it occurred to me to cap off the vacuum line going to the programmer. That addressed the issue, it seems this vacuum check valve is letting in significantly more vacuum than the original did. For now I've decided to downgrade it to a manual blend door control. Later maybe I can try playing with it and try and reduce the vacuum draw but I don't have time for it now.