When you slide the climate selector to AC what happens behind the dash? My problem is when I slide the selector to any of the AC settings the air doesn't come out the dash vents but still blows from the floor vent. It's like there is something unhooked in the dash that doesn't redirect the air to the dash vents.

92 blazer.

 

Update:

Hmmm, after doing some diggin' around some sites the basic operation of the climate control is actuated by the engine vacuum. There has always been a stray vac line on the firewall, turns out this goes thru the firewall to the control switch. Hooked it up to the plenum line to see what would happen. I could hear the sucking sound of the vacuum behind the climate selector, so I opened it up to investigate.



So here's a look at the vacuum control connector. Before I could get a chance to trace the vacuum leak the vacuum control switch came apart in my hands.



As of now, I need to replace this switch and see it that was the cause of the vacuum leak. My guess is the PO was having the same problem with a vac leak so they just disconnected the vacuum line at the plenum.

 

Update:

Replaced the vacuum switch and all is working as should be. This might be a common problem as several switches in the wrecking yard also fell apart as I was removing them.