HVAC heater control alternatives?

[911tracker85]

after extensive reading of threads and trouble shooting the HCV/HVAC heater controller, reached the conclusion I did not want to reach.

apparently the in dash HVAC controller is not working with regard to modulating the HCV. all the air flow flappy actuators work.

I had pulled the glove box to access the solenoids and vacuum lines during troubleshooting.

so got an idea, I knew the recirculating switch/solenoid/flappy was working and verified voltage. but could not get any voltage readings on the HCV leads to that solenoid. so jumper'ed the recirculating switch leads to the HCV solenoid. voila. the recirculating switch will now turn the heat off and on. but no modulation.

my next question is whether there are temp sensors that would create this effect? my 928 had a bad exterior temp sensor, so would go full hot on any setting but full cold. but even on the full cold setting on the 944, still no effect and no voltage on those leads.

so if it is not a bad temp sensor, has anyone tried to install some kind of variable switch to the HCV solenoid rather than pull the dash to replace the HVAC controller?

this may become mute if this also affects the AC. just finished refresh work on the AC and will be refilling the AC system tomorrow. if the AC works, may just leave the HCV controlled by the recirculating switch.

any ideas?

[944 Ecology]

There are three thermistors which provide temp readings to the AC controller (on series 2 cars).

1) in the dash center vent
2) above the glovebox (behind the round grille in the dash)
3) at the AC air intake near the battery.

If any of those is giving the wrong readings, the AC will not act properly. You should check the readings at the connector at the back of the AC controller.

[uvachief]

I have an extra HVAC control unit assembly if you need it. Mountable and works. I replaced it because the defrost switch was starting to stick from time to time. A/c switch still pressed and released when I removed it.