Chevy truck heater

I have a ’91 Scottsdale, 4.3L, and the heat is always on. I can move the controls from cold to hot, a/c to vent, or whatever and all I get is heat. Even with the controls in the off position, hot air comes
through to my feet. Any ideas? Thanks.
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air flow move? If not check the vacuum lines and the vacuum selector switch. If the air flow does move, then there could still be a problem with the vacuum switch, or the blend door is stuck, or the dash pot that moves it is shot. Whitelightning
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No vacuum on this year and model; all electronic. Sounds like either the blend door actuator motor is shot, or the linkage between the motor and door is shot. The doors do tend to get "sticky" over time but if it was stuck and the motor fried I'm sure he would have smelled it!
Doc

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Gesh that's what I get for making an assumption that a 91 full size would be the same as my 91 S-10 Blazer. Whitelightning
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I wish it was a vacuum actuated system. Just more shit to go wrong with an electrical system, and it's harder to service than the vacuum-based systems. Vac lines and pots are usually pretty easy to get at and service, the electric motors are a real bitch and a half to get at..........kinda noisy too.............ol' Blue sounds like a dairy cow mooing when she opens and closes the recirc door, he he he.
Doc
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One thing I always wondered is this. Vacuum leaks can cause a poor running engine, because air is introduced after the air/fuel mixture. Are say the vac controls, or wiper on an older car, "pre-carb"?? Or, can a rough running condition be caused by the failure of one of these puppies? Cuz then that's a dumb ass design....
GMC Gremlin

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Well, a vac port attached above where the fuel/air is physically mixed would not cause drivability issues, because it isn't leaning out the mixture. I supposed if you say a wide open one wouldn't fubar things, it wouldn't - but all I can see is some poor woman stuck on the side of the highway in her hubby's truck because of some heater door - where an electric one would jest fail but the truck would keep movin'.....
GMC Gremlin
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There is no vacuum above the throttle plates, which is why all vacuum ports are located below them or on the maniofold itself.
Doc

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Exactly my point - why not... vacuum with no drawbacks...??
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I think you missed my point. There aren't any vacuum ports "above where the air and fuel are mixed" because there is no vacuum above the throttle plates. Sure, you could plumb one in above the plates, but you'd have no vacuum and whatever was plugged into the other side wouldn't work.
Notice that vacuum decreases as the throttle plates open? Vacuum on most gassers reaches close to zero at WOT, which is the same condition as a vacuum port located above the throttle plates.
No such thing as vacuum with no drawbacks. If a line has vacuum, the air is gunna end up in the intake stream if it springs a leak.
Doc

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"Whitelightning" wrote:
> > > > > > > No vacuum on this year and model; all electronic. Sounds > like either the > > blend door actuator motor is shot, or the linkage between > the motor and > door > > is shot. The doors do tend to get "sticky" over time but if > it was stuck > > and the motor fried I'm sure he would have smelled it! > > > > Doc > > Gesh that's what I get for making an assumption that a 91 > full size would > be the same as my 91 S-10 Blazer. > Whitelightning
The air flow does move between vent, bi-level, heat, etc. I removed the cover that directs air on the blend door and it does move from open to closed between heat/off and ac/vent so the actuator motor and linkage is working. A friend suggested the heater shutoff valve (?) might be stuck open. Thanks, AndrewS
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Too bad yer' truck don't HAVE a heater shutoff valve!
Doc
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I had a similar problem with the AC head unit in my 1990 Scottsdale. I believe that the same system was used in the 1991 model with a re-circulating mode button added perhaps in 1992. If your unit has the re-circulating mode, you are probably using it as a temporary workaround.
Do all of the features of the AC climate control selector seem to work? In other words, does the screen show some movement of the indicator between the icons? If this is the case, the control unit may be working properly, but there may be trouble with the electrical connection.
To access the AC control on my truck, I needed to take out four screws to remove the plastic surround covering the edges of the dashboard. After this, there were a couple of screws holding the AC head unit into the dash. After removing these screws, the AC control could be pulled out of the dash and I could access the clip which connected it to the wiring harness. Go gently when working with these plastic parts because after 14 years of residing under the dashboard, they have probably become brittle. And don't over-tighten the screws when putting the dashboard back together.
It was corrosion in this connection which caused a number of problems (no hot/cold temperature control, no control of air flow, inability to select the AC mode, etc.) with the AC control on my truck. Unplugging and re-plugging the electrical connection solved my problem and it might solve yours. Using a no-residue contact spray is also beneficial. At this point, you can test out the system before re-installing the AC control.
Hope this helps.
PS: I also traced some mysterious problems with the stereo to its connections to the wiring harness. The stereo on the 1990 truck contained three components: The tuner, the equalizer/cassette and the under dash amplifier which was behind the ash tray. Unplug, clean and re-plug all of the stereo connections and this should fix things.
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"One-Shot Scot" wrote:
> > > I have a '91 Scottsdale, 4.3L, and the heat is always on. I > can move > > the controls from cold to hot, a/c to vent, or whatever and > all I get > > is heat. Even with the controls in the off position, hot air > comes > > through to my feet. Any ideas? Thanks. > > > I had a similar problem with the AC head unit in my 1990 > Scottsdale. > I believe that the same system was used in the 1991 model with > a > re-circulating mode button added perhaps in 1992. If your unit > has the > re-circulating mode, you are probably using it as a temporary > workaround. > > Do all of the features of the AC climate control selector seem > to work? > In other words, does the screen show some movement of the > indicator > between the icons? If this is the case, the control unit may > be working > properly, but there may be trouble with the electrical > connection. > > To access the AC control on my truck, I needed to take out > four screws > to remove the plastic surround covering the edges of the > dashboard. > After this, there were a couple of screws holding the AC head > unit into > the dash. After removing these screws, the AC control could be > pulled > out of the dash and I could access the clip which connected it > to the > wiring harness. Go gently when working with these plastic > parts because > after 14 years of residing under the dashboard, they have > probably > become brittle. And don't over-tighten the screws when putting > the > dashboard back together. > > It was corrosion in this connection which caused a number of > problems > (no hot/cold temperature control, no control of air flow, > inability to > select the AC mode, etc.) with the AC control on my truck. > Unplugging > and re-plugging the electrical connection solved my problem > and it might > solve yours. Using a no-residue contact spray is also > beneficial. At > this point, you can test out the system before re-installing > the AC > control. > > Hope this helps. > > PS: I also traced some mysterious problems with the stereo to > its > connections to the wiring harness. The stereo on the 1990 > truck > contained three components: The tuner, the equalizer/cassette > and the > under dash amplifier which was behind the ash tray. Unplug, > clean and > re-plug all of the stereo connections and this should fix > things.
It sounds like the same truck! I can move the display between cold and hot and all the icons work. I’ve also got the mysterious radio problems, so the connections may be the problem. I’ll check and let you know. Thanks! AndrewS
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"AndrewS" wrote: > It sounds like the same truck! I can move the display between > cold and hot and all the icons work. I've also got the > mysterious radio problems, so the connections may be the > problem. I'll check and let you know. > Thanks! > AndrewS
Well, I’ve taken the dash apart, unplugged and cleaned the contacts on the connectors for the heat-a/c controls and I still get heat all the time. I’m stuck.
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sounds like your temp door in your AC/heat system is stuck or not working properly. THe A/C head unit could be screwed up too.
you'll need to locate in the Heat / AC duct work where a door controls the input of heat from the heater and have someone move the controls on the A/C control head to see if this door is moving.
Many of the temp doors are controlled by vaccum (not sure on yours) and the old manual style A/C head unit had a cable that controlled the temp door.
do you get cold air out the A/C vents if you turn on the A/C and select the A/C vents? Does the defrost blow out on the windshield when you select that?
wrote:

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"Elbert3" wrote: > sounds like your temp door in your AC/heat system is stuck or > not > working properly. THe A/C head unit could be screwed up too. > > you'll need to locate in the Heat / AC duct work where a door > controls > the input of heat from the heater and have someone move the > controls > on the A/C control head to see if this door is moving. > > Many of the temp doors are controlled by vaccum (not sure on > yours) > and the old manual style A/C head unit had a cable that > controlled the > temp door. > > do you get cold air out the A/C vents if you turn on the A/C > and > select the A/C vents? Does the defrost blow out on the > windshield > when you select that? > > On 6 Jan 2005 23:32:05 -0500, AndrewS
> wrote: > > >"AndrewS" wrote: > &nbsp;> > It sounds like the same truck! I can move the > display between > &nbsp;> > cold and hot and all the icons work. I've also got > the > &nbsp;> > mysterious radio problems, so the connections may be > the > &nbsp;> > problem. I'll check and let you know. > &nbsp;> > Thanks! > &nbsp;> > AndrewS > > > >Well, I’ve taken the dash apart, unplugged and cleaned the > contacts on > >the connectors for the heat-a/c controls and I still get heat > all the > >time. > >I’m stuck. > > --- > Elbert Clarke > elbert.clarke@**adelphia.net > remove ** to email
No cold air at all. I can move the flow between vent, floor and windshield, but I never get cold air.
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wrote:

I would have to guess then that your A/C control head is faulty if its electronic or you have some issue with the temp door thats part of your A/C heater duct system.
I'm assuming your A/C compressor does work properly?
As far as I know there's not really a way to know for sure if your A/C control head is faulty, unless it displays an error, most of the time its a part swapping game to see if the new control head fixes the problem.
When you move the temp control to full cold you should not have hot air coming out the ducts even if the A/C does not work.
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<<Well, I've taken the dash apart, unplugged and cleaned the contacts on the connectors for the heat-a/c controls and I still get heat all the time. I'm stuck.>>
I don't want to put you to any more trouble. The cause is probably either the control or the motor which operates the vent door. I had my original control replaced under warranty and then when the second one started acting up, I was able to fix it for 6 months at a time by fiddling with the connection.
I do know that GM had so much trouble with that control box that your dealer will probably have it in stock. Last year when I checked availability and price, the unit was in stock at $129.
Whenever the temperature selector was moving in my truck, there was always a little whirring noise which I assumed was a motor moving the heater vent. I doubt that you are hearing any such noise if the temperature is not changing.
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