heater/ac controls

my 99 grand prix gt started about a week ago...........when you turn the a/c or vent on any setting including the defrost it blows out of all the vents. it is like the defrost, heat, a/c, and everything is on at the same time and it doesnt blow very hard. i think it might be the control panel, because the knobs dont seem to be locking in any specific setting. anyone else had this problem? let me know

The selector for heater, vent, defroster, or other settings, simply changes where the air blows out. There is a valve (kind of a way to think about it) in the dash that either closes, or opens, and routes the air to where it should be going according to the selector knob. This valve, or switch of sorts, will get stuck in any particular position sometimes on a variety of GM cars. Usually, the first symptom is that you start to lose fan speeds. Like you may have fan speeds 3,4,&5; but 1 & 2 don't work. Then you either lose other fan speeds, or then lose the defrost, or the ability to get air to your windshield. I believe I have heard of it locking while being completely open before, so that could be what's happening with you. It does have to be taken to professionals, but it doesn't cost much to have it fixed. $50-$130????

I used to have a S-15, and had that same problem. the issue was caused by a vaccum leak. I would check all of your vaccume hoses to see if there was one that was unhooked

just my $.02

If it doesn't blow like it should even on fan speed 5, then it most definitely could be a vacuum issue (to back up that theory).

the switch apearantly was stuck in defrost. i put the knob back on defrost and pushed in kinda hard and turned it and i can get it to work right that way, so im pretty sure it is the control panel. i think the selector knob is stripped out. thanks for the help. if u lose speeds and it only works on one or two speeds that is the blower resistor module. i had to replace it about a year ago

Thanks for that tidbit. Glad to hear you found a resolution.