Y-Body

Found plenty about Automatic HVAC controls, but mine is manually controlled.
The car has not been driven for most of this year (I have been a caregiver out of state) but everything was fine in December 2011.
The car had a battery maintainer on it while it sat in the garage.

The heater blows cold air and the temperature control **** has no effect. A/C is cold (but 47* ambient temp today surely helped there).

Air outlet selector and fan work correctly.
What could it be other than the temperature control switch?
Is the manual HVAC control panel an all-in-one-box unit or three separate switches mounted in a panel?

Experiences, suggestions & WAGs welcomed.

65GGvert

Does the coolant temp reach normal temperature?

Y-Body

Yes, coolant & oil temps were normal.

65GGvert

I'm not close to an expert on manual air/heat systems, but it sounds like your door that blends the air between heated and non heated is not moving to allow in the air that's passing over the heater core. Or possibly someone has blocked or bypassed the heater core so that the hot coolant doesn't pass through the core?

LoneStarFRC

Have you checked your HVAC fuses? Minifuse 18 in particular. Passenger toe-board fuse panel.

Y-Body

The fan and air outlet switches stopped working when I pulled fuse 18.
The outside air/recirculate switch stopped working when I pulled fuse 27.

The Temperature control still does not change the temperature from the heater.

<vent> And I have not been able to realign the fuse box cover enough to get the cover's screw to engage.
It would help if the top 20% of the fuse box was not underneath that flexible trim under the dash & I could see to get the top groove in the cover to align with the lip of the base. </vent>

PhilsFRC

If your unit is truly "dead" you have a problem. The GM p/n is 10447750 and the Delco number is 15-72690. They are NLA from GM. I spent two days e-mailing and calling people and finally found a place in AZ that had two NOS. Paid $390.63. PM me if you want their information as they're not a vendor-maybe the other one is unsold. Only other option is used unit from a part out.

65GGvert

I assume you meant "still does NOT change the temp". I'm not sure how it's wired, but there is a door that moves to allow more or less heated air from the heater coil. You could have a defective control switch or the motor that moves the door may be bad or stuck. We really need someone who has worked on this type HVAC system to help here. If it was the auto system, I'd recommend you disconnect and reconnect the battery and check for codes using the DIC. If it shows any HVAC codes, clear them and try again. That's what I'd try if I were troubleshooting it on my own car.

Y-Body

Thanks for the information.
Yeah, I meant NOT & have changed that.
I'll disconnect the battery tomorrow (& fight the cover again). There are no codes now.

Yeah, I was hoping to find more people who had already fought this particular battle.

I am wondering if the actuator (assuming that it has one as opposed to two for the dual systems) might be bad or has a bad vacuum line (again assuming there is a vacuum line to an actuator.)
Then again, it could be a bad dash control unit since apparently there are not three switches mounted on a panel (Ahhh, the good ol' days).

PhilsFRC

I've seen situations where the diverter door can stick due to age and the foam edge seal turning into mush, thereby sort of locking it in place. Determining that would require a fairly significant teardown. PM'd you on the information where I got my "new" part.

Y-Body

Got it. Thank you.
After looking around the 'net, it seems there may be more than one manual HVAC control unit.
Mine is a '99. What year is yours?

Bill Curlee

Here is the schematic that you need to troubleshoot this circuit.

Bill Curlee

Your SINGLE Actuator Controller is located on the left side of the air box. If you look under the drivers side dash on the side of the air box, you will see it:

Your single manual actuator is on the LEFT side circled in red. You will NOT have the one on the RIGHT circled in red.

Pretty simple:









Turn the controller fully HOT and fully COLD and see if the shaft that moves the door moves. If it doesnt move, see if you can hear the small electric motor inside the controller is running.. Here is what happens when the main gear cracks:






If its cracked, it will not move the damper temp control door

BC

Bill Curlee

IMPORTANT!!! Read the two test points on the top of fuse 18 to chassis ground with the ignition switch ON. Make SURE that you see FULL battery voltage on each test point.

That fuse is ppowered by the output of the ignition switch. A known failure item..

BC

PhilsFRC

Mine is a '99. Part number referenced is the correct one for your car.

Here's the parts blowup:
http://parts.nalleygmc.com/showAssem...roduct=2821101
#5 is the auto/dual zone controller and #11 is the manual unit. If you look closely, they are both the same (auto) p/n, which is impossible, since the two are not interchangeable. The research I did came up with the number I listed above, and the part I have in hand is a manual controller. FWIW.

Y-Body

Minorl update
I can hear the motor running. Run time is directly proportional to the degrees of switch rotation.
Wilco
It's worth a lot to me.


It's 40* & wet today. I have to move the car onto the driveway to open the door far enough to lie on the concrete so I can get under the dash, so not much going to happen today.
I did find a picture of the rear of the panel:
[IMG][/IMG]

Bill Curlee

I dont think that is part of a C5.. Could be wrong. All my cars have been Dual Zone HVAC but, the actuator for the manual HVAC should not be much different than a dual zone except you only have one actuator and one temp door..

BC

PhilsFRC

Just took mine out of the box and that's essentially it. HOWEVER the one pictured is BROKEN. The round thing on the left is a vacuum distribution valve of some sort. There is an assembly that attaches to the silver colored shaft, that has what I'll call a "vacuum distribution manifold" (for want of a better term) that has 6 vacuum nipples on it.

Bill Curlee

OH,,,,, Thats the CONTROL HEAD!

Y-Body

I had forgotten that the battery was replaced (disconnected) in June when I returned for a couple of days.

Since the motor runs when the temp control is turned and the motor runs longer when the control is turned further, it seems that the control panel is functioning properly. (Which is actually too bad since replacing the controls would be the easiest repair.) But the car had not been cranked for two days when I listened, so any required vacuum-assist was probably not available

So IF the switch is good, what does that leave?

• There are no codes. Does the Dual Zone always throw codes when it is bad?
• PhilsFRC pointed out that one of the control switches has a vacuum "octopus". That may be to the air output selector system.
  But there appears to be two other vacuum connectors on the lower rear center of the panel where the temp switch is located. What is the easiest & fastest way to check vacuum in the HVAC switching system?
  What else might be in play (or not working properly)?
• ?

I am time limited because I have to return out of state. Anyway, the idea of my tearing out the dash just plain intimidates me. I did see references to accessing the driver's actuator by removing the knee bolster.