Heater Control Assembly no good.

[SS5800]

Anyone else have this problem? My LO-HI control works, and the Cold-Hot control works but the dial to change where it blows to is smoked.

I checked the plugs its all plugged in, Is there anyway to fix this because a new one is fricken $100. Seems a bit ridiculous

 

[79powerwagon]

eBay has a bunch of them on there. Must be a fairly common part to fail, judging by the amount of eBay stores selling them. It's all vacuum controlled, so check your vacuum lines, too.

 

[corvhoe7795]

There's no vacuum to the heater AC control. It's all electric and a non servicable control unit. Take the unit out and you'll see wires and 3 black boxes behind the knobs. You could take the one box apart where the wires from the control knob go to this box, you might find something just dirty is all. Like a dirty electrical contact.

 

[79powerwagon]

There's no vacuum to the heater AC control. It's all electric and a non servicable control unit.

Can you link to an image or diagram? Unless it's pure coincidence, my sluggish controls suddenly change to their proper position/function when I have a significant difference in engine vacuum (WOT, full decel)...

I don't know, that's why I am asking! This is my first GM since my 68 Impala:ack:

 

[corvhoe7795]

I took 2 pictures of my dad's old heater/AC controller. He has a 1995 Tahoe too and changed his controller about 2 years ago with a good used one. Anyway, to insert the 2 pictures it's asking me for a URL of the images, I don't know what to fill in after the http:// As soon as I find out what to do I'll get back to ya.

 

[corvhoe7795]

heater control pictures

Heres a couple pictures of the heater / AC controller. My dad also has a 1995 Tahoe and this is his old one that quit working and was replaced. We forget what the actual problem was, it was around 2 years ago. You can see it's all electrical and there's no vaccum to it. There's tiny resistors on the circuit board and probably these are the culprits that make the controller unoperative. Oh, he bought a good used one from ebay and it's still working great. Hope the attached pictures help.

 

[sasquatch094]

mines a 95 and doesnt look like that........

 

[swanie2000]

mines a 95 and doesnt look like that........

Mine's a 1995 Tahoe, and that looks perfect compared to mine.


My unit had brittle plastic, and the 2 POT's on the board, were not seated into the plastic knobs correctly. It took some time, and some 5 minute epoxy to repair mine, but it works good now...

Swanie

 

[79powerwagon]

Hmmm, interesting! Thanks for the pictures! I bet the actual servos for the defrost/vent/heat are vacuum operated/powered, driving by the electronic controls... Again, just a guess until I get a manual...

 

[swanie2000]

Hmmm, interesting! Thanks for the pictures! I bet the actual servos for the defrost/vent/heat are vacuum operated/powered, driving by the electronic controls... Again, just a guess until I get a manual...

NOPE!
There are three servo actuators, and all three are electric. I had issues with two of mine, one I replaced, and the second, I took the main gear from the first one, to replace the cracked gear on the second.


The first servo is located just up from the gas pedal, this one directs the air flow up to the windshield, out the main dash vents, and down to the floor.

The second one is behind the ashtray, it is used to blend the hot and cold air.

The third one is way up behind the glove box, and it is used to select inside/outside air, and also the MAX air feature on the AC "HI" setting.

Swanie

 

[79powerwagon]

Then it must just be coincidence that the amount of engine vacuum changes the position of my controls. I paid particular attention to it yesterday as I was driving around, and engine vacuum changes was when the controls changed.

Believe me, I'm not arguing here, I'm trying to learn.

A friend of mine has a 05 Ram truck, and at WOT, his defrosters go one regardless of the selector switch. Then when he backs off the throttle, it goes back to where it's supposed to be. Another friend has a 03 Ram van work truck, it does the same thing.

My Yukon does this too, that's why I ask these questions. Perhaps it a voltage thing (at high rpms, but that doesn't explain the decel operation).

Curious!

 

[swanie2000]

Then it must just be coincidence that the amount of engine vacuum changes the position of my controls. I paid particular attention to it yesterday as I was driving around, and engine vacuum changes was when the controls changed.

Believe me, I'm not arguing here, I'm trying to learn.

A friend of mine has a 05 Ram truck, and at WOT, his defrosters go one regardless of the selector switch. Then when he backs off the throttle, it goes back to where it's supposed to be. Another friend has a 03 Ram van work truck, it does the same thing.

My Yukon does this too, that's why I ask these questions. Perhaps it a voltage thing (at high rpms, but that doesn't explain the decel operation).

Curious!

No worries! I will be the first to admit that I do not know everything about my 95 Tahoe, I have only had it for a couple of months. I have had a lot of experience with my trucks HVAC recently, as it wasn’t working when I bought it. I have personally visited all three of these servos, and replaced one, and fixed the second. I was only posting MY PERSONAL experience with my 95 Tahoe, that’s all. I am here to learn as well….

That being said, my HVAC would do weird things, such as under the passenger side glove box, I could hear a door opening and closing, back and forth, every minute or so. This door turned out to be the door that selected outside air or inside air for the blower. So different vehicle speeds, would have different air pressure on the door, and it would not open and close as often while driving. As it turned out, the actuator servo for this door, had the output gear cracked, and the main output shaft could slip back closed, if you pushed on the door, or possible if the air pressure on the door was great enough? When I looked at mine, you could see the door close, the servo would stop, then the door would fall open again, then the servo would try to close it again, and so on….

I don’t know if this is your problem or not, but I thought it may help someone here.

Swanie

 

[ConnieRS]

I seem to be having the same problem. One day I got in my 95 Yukon and my HVAC unit was only working for the floor and defrost positions. I was told it was my unit but I am not sure as to if it is that or the mode actuator by the gas pedal.

 

[bsamoul]

If my Hi-lo isn't working right, would it make sense to replace the switch? It cuts out on the setting right before high.

 

[swanie2000]

I seem to be having the same problem. One day I got in my 95 Yukon and my HVAC unit was only working for the floor and defrost positions. I was told it was my unit but I am not sure as to if it is that or the mode actuator by the gas pedal.

Based on what I learned by messing with the acuator by the gas pedal, the floor is one position, the defrost is the extreme opposite position, and the main dash vents, is somewhere in between. See for yourself, take the actuator off, and move it by hand.

While you have it off, pop it apart, and clean the little pot inside, that is controlled by the gear shaft. This could be dirty, and/or have carbon build up in the center position. It is worth a try.

Also, you can try to clean the pot on the vent selector, it could have the same problem. Basically, get some electrical contact cleaner, and spray it into the moving parts of the pot. Some cleaner will get in there to the wiper that makes contact. Just take care not to get the electrical contact cleaner on anything plastic, as some cleaners will attack plastic.

Michael

 

[swanie2000]

If my Hi-lo isn't working right, would it make sense to replace the switch? It cuts out on the setting right before high.

You could replace the switch,(if you happen to have one handy) but I have read of others here saying your problem sounds like it was the resistor pack? You may want to search a little and see if you can find that. I am not completely sure where the resistor pack is at.

 

[SS5800]

Where are the pot and actuator on a 1996 2 dr tahoe?

 

[swanie2000]

Where are the pot and actuator on a 1996 2 dr tahoe?

A "pot" is an electrical term, short for potentiometer. It is simply, a variable resistor.

On my 95 Tahoe... not sure about the 96 year, but I would bet they are very similar...

There is one pot, it is inside the actuator it's self. It is mounted on the circuit board, under all the drive gears. You will need to remove actuator from truck, and completely take the actuator apart, on your work bench, to get at the pot in there. This pot, from the best I can tell, is a feedback resistor, and it tells the actuator it has fully traveled from one side to the other. With this theory in mind, It is possible to see how a dirty pot, could fail to tell the actuator it needs to move, etc.

On the HVAC control unit, there are 2 pots mounted on the main circuit board, and their shafts go out to the control knobs. You will need to take most of this apart, as well, to get at them.


Michael

 

[bitterspleaf]

You could replace the switch,(if you happen to have one handy) but I have read of others here saying your problem sounds like it was the resistor pack? You may want to search a little and see if you can find that. I am not completely sure where the resistor pack is at.

I'd start with by testing that resistor pack directly behind the glove box, 2 bolts.