ORIGINAL: mk378

There's a motor that controls which vents the air will come out of. It's electric, not vacuum. When you push the buttons on the control panel, does the corresponding light come on? Check that everything is plugged in, if so could be the motor or the control panel. The motor is on the heater box sort of behind the control panel. I think it can be removed without taking the dash out by reaching way up from the floorboards on the left side.

The temperature lever is purely mechanical. Check that the water valve under the hood opens fully (lever moves back toward the firewall) when you put the lever on hot. If it does the heater core may be restricted. Disconnect the heater hoses and flush it with water to check for restricted flow. This is assuming of course that the engine reaches proper operating temperature.