Hi,
I have a '98 blazer. The heat ALWAYS comes out the vents on the dash. It will come out on the floor, or the defrost as well, but the vents are always on.
I located the two vacuum valves under the dash, drivers side. Both valves are operating correctly, however, the “Mode” valve which controls the vents does not have vacuum on the front port. All other vacuum hoses have vacuum ~10”. So I believe the source of the problem is the lack of vacuum on the specific hose (yellow).

I have the automatic HVAC unit, so there is a bank of solenoids that control the vacuum to each port under the front of the dash.

So here’s my questions for anyone that can help:

How do I determine if the problem is the solenoids, or the HVAC head unit in the dash?

If it is the solenoid bank, how do I remove it and where exactly is it? It appears I may need to remove the entire dash to get this small box out that’s may be right under/behind the ash tray?

Any help would be appreciated.

 

Somebody out there has to know something about this????