Hey all! For the first time in a few years I tried to drive my Z in the winter cold and noticed the heat does not work! I dug around through the forum and found a few posts about rebuilding valves and lots of unobtainium parts. Before I got too deep I wanted to make sure I'm troubleshooting correctly. Am I correct in that there are two valves on a 77-- the vacuum operated one at the firewall and a cable operated one closer to the heater core?

Is there an easy way to isolate and test for clogged heater core vs bad cable operated valve vs bad vacuum operated valve?

My car does have AC if that matters for troubleshooting (though I've never tried to use it).

6 hours ago, sboy79 said:

Am I correct in that there are two valves on a 77-- the vacuum operated one at the firewall and a cable operated one closer to the heater core?

Is there an easy way to isolate and test for clogged heater core vs bad cable operated valve vs bad vacuum operated valve?

My car does have AC if that matters for troubleshooting

There are two water control valves for AC cars. One simple thing that you can do is to just stick your head under the dash and watch what happens. Not uncommon for the water **** cable to get bent and stop moving the ****. And the vacuum **** works on vacuum of course, which comes from the vacuum tank. I had a hard time keeping the supply line to my tank from splitting. No vacuum, no heat. That was my clue. You have to check all of those things.

An IR gun might help you locate where the warm hoses stop and the cold hoses start

14 hours ago, Patcon said:

An IR gun might help you locate where the warm hoses stop and the cold hoses start

I had a similar thought about checking hose temperatures but realized that if the valves are closed flow will be stopped. No way to tell if it's valves or a core blockage just by hose temperature.

These are both great places to start. Can you see the two valves operate with the blower assembly installed or does that need to be removed?

It's cramped but I think that you can use vision and feel to determine if they are working correctly. You'll probably see old crusty hose and signs of leakage and end up on a difficult weeks or months long repair project. Beware and good luck.