dturley

The air direction does not change on my 96 Blazer. It will only blow on the windshield and on my feet. I understand that this is vacuum operated. On the back of the control switch I am seeing 5 vacuum lines (orange, blue, gray, brown and black). I have been able to trace the orange, blue and gray lines. I'm not quite sure what I need to ask, but I think my questions are: Where is the main source of vacuum located on the manifold and where does it come through the firewall? Which colored vacuum line is responsible for changing the air direction?

MT-2500

Black/gray is the engine vacuum source.
The rest is in your mail box.

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Remember proper testing gives us the answer to many problems.
MT

old_master

With no vacuum present at the control switch, the HVAC system defaults to defrost. A black vacuum line, approximately 1/4" in diameter, runs from the intake manifold, possibly near the PCV valve, to a vacuum tee/check valve. From the tee, one line runs to a vacuum reservoir located under the hood. The other line goes through the bulkhead, (firewall) near the center, to the interior and then to the control switch. With the vacuum connector unplugged at the switch, there should be vacuum to one hose while the engine is running.