Classic Muscle

I have a 77 Corvette that blows heat out the defroster and floorboard but nothing out the center or side vents. When I switch the selector to AC then air flows through the vents. Could this be a bad "Heater Air Conditioning Control Vacuum Switch"? Or should I look for some other problem?

kansas123

If you are wanting warm air from the vents at the same time warm air is coming from the defroster/floor, I am not sure the systems on these cars were designed to do that. I'm sure you will receive word soon from some experts soon. Is there a bi-level selection on your HVAC control switch? Seems like that might be what you are looking for?

Classic Muscle

I've tried every setting on the seletor switch and the only time any air at all will come out of the center and side vents is on the AC setting.

kansas123

On a '72, when the Bi-level selection chosen, "only outside air flows into the system and the air flow is directed between the dash and floor outlets with slightly warmer air coming from the floor outlets." If this is not happening, then there may be something wrong with either the switch or the vacuum lines that are plugged into the switch. Perhaps one has come off. The only way to know is to gain access to the workings of the switch by removing the console cover.

Classic Muscle

I have most of the dash and console out of the car now. The vacuum hoses going to the thing connected to the switch feel and look good from a quick inspection. The weather here in NC hasn't been so great the last couple of weeks but I plan on uncovering her tomorrow and tinkering a bit. There is no air coming from the vents at all unless it is on the AC setting I'm positive of that. When it's on the AC setting it blows pretty strong considering it probably needs new foam striping installed on each duct work fitting.