Recently the heat has been working less and less frequently, the water valve is working great which leaves the good old Tempmatic. Early next week I'll be diving into it and doing proper diagnosis following the manual, but based on what I've been reading here it's very likely the vacuum check relay. As its a common problem with Tempmatics in general it seemed like starting a thread about it would be beneficial, even if it ends up not being the problem in my case.

I've tried doing a preliminary part search for an exact replacement but found nothing, maybe I'm looking at the wrong item? If an aftermarket equivalent isn't available, besides ripping it out how can this problem be fixed?

 

So I’ve had my ‘77 Pace Car and my dad’s ‘77 98 apart several times. What is this relay that you speak of? I don’t remember there being one and both are the auto temp control.

trying to understand to help. I worked on fixing both vehicles so maybe I can help.

jerry

 

This one:




Like I said I don't know for sure yet that this is the problem and I won't have time for a few days to look at it, but from what I've been reading it's very likely as it's a very common problem. Even if it's not the problem in my case, someone will have this issue at some point so either way it's still a benefit to post this thread.

 

Was able to do some work on it today to verify, the check valve is definitely bad. I plugged the vacuum line directly into the vacuum motor and got heat again, replaced all the vacuum lines as they were and suddenly no heat. Now I need to either find an exact replacement relay, which is probably impossible unless anyone has some leads, or find a functionally equivalent vacuum check valve and juri-rig it in.

 

Those things were a common enough failure item that the Buick dealer here kept a couple on the shelf all the time. As many as I bought I can't remember the part #. They were cheap until GM obsoleted them 10 years ago or so. Last one I bought on secondary market was all over top of 50 bucks.

Here's a workaround till you can find one. Connect the vacuum lines as you did to get full heat. Splice a vacuum tee into the hose and run another length of hose into the glovebox. Plug the open end of that tube with a golf tee. If you want cool air, unplug the tee.

Rigged? You bet. An Oldsmobile Zone Service Manager taught me that trick.

Be glad it's a Tempmatic and not a Comfortron.

 

Part # 16002275. Delco # 15-7055.

 

Excellent, got one on the way. I also noticed something odd, it looks like the temp slider cable somehow isn't attached to anything. I'm pretty sure it's supposed to hook onto that long vertical lever running down the center on the front of the unit. Any suggestions for retaining clips I could get at the hardware store to fix it?

 

Turns out there wasn't a clip, the eye of the cable just fits onto the vertical bar, not sure how it managed to pop out at some point. Anyway I finally was able to dig out the programmer and install the new vacuum relay. So far on my drive to work it seems to be working normally again.