Ken P

I had something strange happen recently. I was running my daughter around on errands in the 928.
It was a cool morning and I wanted to add a little heat. So I slid the heat control over to all the way hot and the fan control up a notch or two.

All I got was cool air out of the vents.
On the '89 GT.

I did recently change the water valve and the two small diaphragms, in the pods, behind the center console.
Of course I had it all apart.... I did put it back together and tested all of the vacuum lines and they all held. I had driven it a couple of times before the shifter and clutch work and verified the heat worked well.

The vacuum work was done just over a month ago. Since then I worked on the shifter ball cup and linkage and R&R'd the clutch.

So ... I got home and pulled off the drivers side panel to take a look thinking maybe a vacuum line had come loose. Nope everything looked fine. Idling in the garage I started to get heat, I was playing with the sliders on the Control unit. So I backed out to go for a little drive and the air went cool again??
Pulled back in and took of the air filter housing to verify the water valve was working. The only thing I noticed is that it would take 5 - 7 seconds from moving the slider from full hot to full cold before the heater valve would open or close. It did follow the slider for heat or cool, but with the 5 - 7 second delay.

I put it back together and it has not happened again , yet...

So the things that could cause this;
1) Vacuum - very likely to have a leak, but the wrong failure mode. A no vacuum failure should cause heated, not cool air. .
2) Low coolant level - The next day I checked the coolant level and it was about 3/4 of an inch lower than I thought it should be. I topped it up to the seam on the reservoir. I had lost some coolant when I changed the heater valve.
3) Electrical contacts in the Control unit - possible. By moving the control sliders back and forth I may have resolved this issue. restored good electrical contact by moving the sliders.
4) The cabin air sensor - When I put the console back together maybe I did not get this back together securely? If this is not pulling in cabin air, could this cause the symptoms I have seen?

Has anyone else experienced an issue like this? What might it be?
Am I missing something to diagnose?

Maybe the car missed being driven for the last 3 weeks while waiting on clutch parts and was letting me know about it. It had been pretty snowy here, we had gotten about two feet of snow. All melted off now though.

Thanks,
Ken