No heat problem finally solved!
 

When I bought my 86 944 na, I had heat all the time. The clip in the footwell had broken and it had defaulted to full heat. Ran me out of the car. I installed a new clip and guess what? No heat 95% of the time. It was coming and going and mainly not coming. Checked the vacuum lines. Found one old one to the heater core frayed and barely on. Fixed that. Had heat for a day. Thought I had solved it. Heat disappeared the next day. Assumed it was the heater core. Removed and replaced that during the top end engine rebuild. Had heat for a week and then no heat. Kevin Kaminski told me it was the HVAC control uit in the dash. He had swapped one with a known working customers in his shop. I bought several off Pelican Parts Classifieds. Swapeed all of them in and out over time. One had to work right? No change in the no heat problem. I was beyond irritated.

I kept driving by this little import repair shop not far from my house. I saw one of the mechanics had an early 944 na. Figured I would give it a shot. Dropped it off to him. 2 business days later - he called. It was a defective HVAC control unit. He was able to source a rebuilt or reconditioned unit for less than $150. Installed it and voila, I have heat now. Just passing this on as a warning about buyung used parts - even on Pelican. Also, maybe it will help trouble shoot someone else's no heat problem. Good luck!

I have a similar problem with my 87S.

I replaced one heater clip in the drivers footwell, and found a vacuum line off under the air duct I had once removed to replace the wiper motor. If I turn the temp down to less than 25% I hear a click in the control unit and the heat relents. Something is still not right.

I think there are two other clips somewhere I have never seen that could be bad, as well as a possible problem with the control unit.

I would think the control unit might be repairable if it has bad solder joints, in fact I can recall a post about how the unit could be rehab'd.

Edit: Found the 2nd clip in drivers footwell, but pelican says there are 3 per car...

Clarkes also mentions the following: Typically this is caused by a dirty interior air temperature sensor. There is a small fan that supplies air flow to the interior air temperature sensor. It's located behind the small round vent next to the cigarette lighter. Underneath the dash follow that tube toward the firewall and you'll locate the interior temperature sensor. See pictures in HVAC-01 for sensor location.

So let's make this an all-Virginia thread..
Have either of you gents yet replaced your original Heater Control Valve in the engine bay?
(next project on my list)

Same question for any members not from the Old Dominion?
Merry, merry to all..

I replaced mine when I did the top end rebuild in 2011.

Early cars don't have that problem. They're full on when the plastic clip on the rear of the unit fails to hold the cable any longer. I deal with it. The a/c system when on shuts down the hot air flow.

Congrats on getting it solved. Do it yourself next time, you slacker.:D

I did...three times and all the dang units didn't work.

I just finished up opening up, I mean, cracking up the dash, to clean the air temperature sensor vent and hose. So my heat is now working flawlessly. Next stop Pelican to order the heater face plate that got destroyed in the process.

Also installed one new rear speaker so all 4 now work, and installed a new washer pump so I will have bug juice this winter...

What a nice day it was in Virginny.

I need to do the washer motor also. Mine sounds like 2 squirrels fighting over nuts.