So here it is. I have a 97 silverado, 4x4, 1500, 350, auto. It has manual heat/ac. It is electronic not vacum. One day air would only flow from the floor duct no matter where I put the selector. It must be the mode actuator right? Wrong, I changed it and nothing. So it must be the HVAC head unit right? Wrong, I changed it and nothing. Then it started working again until I pushed the A/C button or recirc button. Once I push one of those buttons it goes right back to floor. I shut off the the fan and tap on the HVAC head unit and turn it back on and air blows from the vent I want it to until I push A/C or recirc. The buttons don't light up at all. The air just goes immediately to floor. I don't get it. Any help would be greatly appreciated. Thanks.

Scott

 

check the plug that goes to the control unit....they get worn and fit loose after awhile and then dont make good contact. there is no doubt its an electrical problem....fairly common

 

The larger plug? Is it replaceable?

 

I need to pull mine anyway so I will do that and let you know....but yes I think it is replaceable