heater / a/c control problem
 

1986 944 Turbo. I've been having a problem with the heat and a/c working. Regardless of where I set the temp, sometimes I have a/c, and sometimes I have heat. So far, I have check the plastic clip, and that is intact (replaced it a few years ago), and I have replaced the hvac unit in the dash. Still I get the same thing, seems to be no control over what it wants to kick out. BTW, the a/c works and blows cold, when it decides to give me a/c. Same with the heat.

Any thoughts?

Bump

I have the same problem. My car is also a 1986 944T, but I don't have A/C on mine.

I get full heat most of the time, and suddenly the system will start working normal and I can regulate the heat. More and more often it is only full heat.

I have checked the plastic clip, installed a new heater control valve and checked the vacuum lines.

I would suspect the control unit itself, or the interior temp sensor.

It's definitely a vacuum line. It sounds like the heater control valve is randomly opening. IIRC it fails open.

I just finished a build of an 86 951 for DE. all new vac lines, new HCV, and my vac/boost gauge shows excellent vac. so far have not completed the rebuild of the AC. AC on a DE car? why not.:D

but from time to time it will start out blowing hot air. if I rotate the HVAC temp knob to hot and back to cold, it will then stop the hot air. so I am guessing the HVAC head unit is a little flakey. but have not pursued further.

refreshed an 87 944S and sold to my Bro. initially it blew HOT all the time. replaced the HCV but also found not getting VAC to the HCV. after testing from inside the car, concluded the vac line to the HCV was good, but the HVAC head unit inop. for a temp fix, moved the HCV vac line to the RECIRCULATE vac fitting. out and it shuts off the heat. in and HOT. with the heat off, the AC worked fine. just no fine control over cold or hot.

this one is back at the shop for new fuel lines and I got another HVAC head unit to install.

PS. if this does now work properly, need to test the temp sensor.