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?

StoogeMoe

You don't have to pull the dash to get the controller out. It's pretty simple. The hardest part is not breaking the plastic trim piece when you pry it out. Then the controller is held in by four bolts.

After you remove the controller and unplug the connectors, you can measure the resistance for the temperature sensors to see if they are within spec. As far as I know, the HCV is not modulated. The temperature is controlled by one of the flaps. It's the one on the bottom closest to the cabin. Check that the control rod is in place. You can also supply voltage to the proper pins and make the motor move to make sure it works. Clark's Garage has most of the details. The FSM has a section also.

911tracker85

thanks, got the impression had to pull the dash.

do you know where the info is to test the temp sensor resistance? what pins and what resistance to expect? do not recall seeing that in the WSM, but may be in another section than the one I was using so far.

using the recirculating switch is controlling the HCV is working for now. did not know how the temp gets modulated.

when I started chasing this, went through all the issues covered in Clark's garage tech tips. all that stuff is good.

unfortunately the used AC condenser leaks, so waiting for a reply from the ebay seller about a replacement or return.

StoogeMoe

All the resistance info is in the WSM. I think it's near the end under the body sections. If I recall, it also tells you what pins at the servo motors to apply 12V to move the motors.