heater wont turn off?

[wally91vhevrolet]

I have a 91 silverado and when i turn my heater off itll stay off for 5 mins n then turn on on the floor. it doesnt show it on on the display? sometimes the triangles flash n wont let me turn it from heat to cold. i dont have a compressor on it any more i installed a bypass pulley cause all the bs the compressor was causin me. but this was a prob long be4 that. would it be a relay? sometimes it kicks on when i jump on the throttle. it never blows cold either only hot. i wouldnt mind so much if it didnt blow so damn hot i have to keep my windows down. i havnt tried much cept disconnecting the battery to reset it and turning it off and on repeatedly. also pulled the fuse and checked connections on back of the control unit (which is all digital on my 91 **not mechanical**) any help is appreciated.

[skipr]

Check that your blower motor resistor coils are not touching each other, and check the therm-limit resistor in front blower.

[67malibu]

Check the damper that allows air to flow over the heater core. They tend to get stuck.

[benw]

I had a similar problem. my heater blows hot air out on the floor continuously when the truck is running. It doesnt matter what the temp is set for, it just blows out hot air.

[mbumgua]

The heater/AC controller has a circut board in it if it goes bad these kind of things can happen. GM had lots of problems with these even when they were new. Junkyards often have these for 10-20 bucks. Get a known good one and swap with yours. This can rule out the control unit as your problem. Also a bad contact where the control plugs in can cause problems. Good luck!

[wally91vhevrolet]

wouldnt pulling the fuse and turning off the control unit make the heat turn off if the control unit was the problem? i pulled the fuse and it still blows heat

[mbumgua]

Yes --that should stop it if it is the controller-- so maybe the quick fix is to put a ball valve in the heater hose to shut off hot water to the heater core when you don't need heat. you may have a vacuum leak in a heater vacuum control line--also the flaps that control air flow could be stuck or the motor that controls them broken. Best and easiest is to put in the ball valve.

[wally91vhevrolet]

I pulled out all 3 relays behind the glove compartment and i cant turn the heat on at all.... but for some reason when im driving it STILL blows heat on the floor? shouldnt pulling the relays cut all power to the blower and not let it work at all? i would expect it to let some heat seap out but blow out? i dont understand... i might try the ball valve thing next.. where can i purchase the ball valve and how hard is it to install?

[67malibu]

In either 92 or 94, GM finally made it where you could shut off the outside vent. From 88 to at least 91, you can't shut off the outside vent so when you are going down the road, you are getting airflow into the cab (on your feet if nothing is on.) As you turn off the ignition each time, you will hear the vent closing for a few seconds. The most common cause for your problem is the damper that allows air to flow across the heater core gets stuck open. Since antifreeze always flows through the core at operating temperature and the outside vent opens, you get hot air blowing in on your feet as you go down the road. Check to see if the heat is only blowing in while you're up to speed or if it is blowing while sitting still.

[wally91vhevrolet]

it only blows when im up to speed... ill check the damper door for the heater core... right now i got rubber tape covering the holes at the feet lol but u have 2 do what u gotta do ya know.. isnt there a motor that turns the damper door? could this have gone out?