LannyL81

On my '95, do not get much heat out. Have flushed the heater core and had good flow, so that is not the problem.

It seems that the air mix door motor is not moving the door between the heater core and the evap coil. I have it out, but have no way of testing it. The C68 Electronic Temp control self test all came back good with no failure codes, so I am assuming that this is good as this is what drives the motor.

Has anyone had to replace this part before?

Thanks,
LannyL81

SunCr

Never replaced one - usually it's the linkage that breaks and the only trouble code is if the return signal opens or shorts. Troubleshooting ('90 and up) is best done with a bidirectional scanner through the CCM link. That will emulate the Control Panel and you can send commands to fully open and close the door. If it doesn't work, suspect the Programmer. If it does, suspect the Controls or the Serial Data Lines. If you don't have access to one, might be worth it to see what the Dealer's flatrate is to do it for you. Otherwise, at 90, it should be completely blocking the a/c evaporator - 60 the opposite. Verify by removing the Blower Module from the Evaporator Case and looking inside to observe the Door. If it's moving correctly, your core is plugged up (sometimes they can't be flushed) or I believe your Year has an orifice from the coolant source on the inlet line and a couple around here have found it plugged up.

LannyL81

On this '95 there is no linkage, its a direct connection to the motor module.
I had the motor module in my hand while I went between hot and cool on the temp setting...and the motor never moved. I can rotate the air mix door by using my fingers, so I now that it is not jam'ed or anything. I am not able to turn the motor with fingers though.

According to the FSM schematics there are two battery inputs into this motor with resistors (of unknow value), so I do not want to put +12Vdc across it to try to test test it.

Guess I will just get a new one and see what happens. Would not be the first time I have replaced a perfectly good part.

LannyL81

James in MD

This is the same problem that I posted about a couple of days ago. I recently purchased a 91 w/LT1, and am experiencing the problems that you have described. The system has been flushed, codes checked in the control moduel (no faults), and the temp door doesn't move freely. I'm going to go back and check for door position at 60 and 90 degrees. This is most baffling.

Corvette Kid

Although I haven't had to work on mine and so haven't checked the manual, you need to consult one. Testing an actuator for a blend door or anything else is very simple. The actuator has a set number of positions, each of which are determined by a given voltage reading. If the correct voltage is there for each position, the module is good. If the actuator on the blend door does not respond properly to the various voltage levels, it is defective.

65Z01

If the motor drive voltage is varied to set door position, perhaps you can jumper between the connector and the motor. Then you can measure how drive voltage varies between the 60/90 deg settings, with the resistors in the circuit.

Then, if the drive voltages seem correct you could be assured that the motor is bad.

enventr

laniL81,
If you set heater to 90 degrees do you get more heat or is it still poor?

LannyL81

I was able to test the air mix door motor by applying +12V through a resistor. I looked at the schematic again and saw that I had mistaken the action of the switching of the power supply to the motor. It does indeed work off of +12Vdc through a resistor to ground.

Took mine apart and applied +12Vdc and the was able to see the motor moves in both directions. I check harness and it is good as well. I still need to check the circuit board within the motor module for continunity between the motor itself and the harness connector pins to make sure I do not have a break there.
If the circuit board is good, then what is at fault in my car and probably James in MD is that the HVAC Programmer has failed, as it provides the power to the motor module.
The HVAC head control should be reporting a failure as there is a positon feedback circuit within the motor module that tells the systems that the door is not moving.

Putting the HVAC into diagnostic mode, selecting the temperature door test should show this.

But I did have heat this morning as I have the motor module off and I can move the air mix door using fingers. So I just put it all the way to the heat position and drove to work WITH heat. Of course I could not regulate the temp with the temp setting...just had to open the window.

I plann on pulling out the HVAC Programmer and checking solder connections first before getting a reman one ($120). Getting to the HVAC Programmer is not fun..

James in MD....I suggest you check the temp door values on your HVAC control head. If you need instructions on how to, just ask.

LannyL81

VenkmanP

Tell us more about whatever you're getting at here. Do you know what causes this problem?

Mine (C68) has always blown lukewarm at any temp other than max or min. At max it blows full hot. At min it blows full cold. In between is pretty much one temperature.

I've figured it was probably a bad interior temp sensor but it hasn't ever bothered me enough to dig into it. This winter I have the dash apart and will be investigating this problem.

LannyL81

After taking the motor module apart and testing the motor with +12Vdc and seeing that it moves it both directions....I plugged it back into the car and this time when I changed the temp settings between 60 and 90....the motor comes on.

Guess the HVAC Programmer is working fine. Only thing I can think of was that the solder connections on the motor are not making good contact and my probing around on them clean the connect enough to get it to work.

I plan on hitting the two solder joints with a solder iron to reflow the joints and test it again in the car. The motor housing itself is very oxide which I think is from condensation dripping down the temp door pivot shaft and into the motor module. This motor is just a little dc motor. I will post a picture of the insides later tonight, as I took a picture of it before I took it apart.


Here is what the air mix or temperature door motor module looks like inside
http://i136.photobucket.com/albums/q...1/P1280003.jpg

LannyL81

LannyL81

See link in above post

STL94LT1

From what I've read the electronic climate control needs 3 minutes to relearn after the battery has been disconnected and reconnected. Maybe diconnect the battery and reconnect, then let the car run for 3 minutes before adjusting the climate control. I need to try this on my car, because it is starting to have the same symptoms you describe.

Just a thought.
-Mike

enventr

My 95 has the same problem but the heat is good for 10- 15 minutes then it gets cold(set on 78 degrees) if I put temp. to 90 degrees it gets real hot.I checked position of ambient temp. sensor-that was good.I know I had a new radiator put in recently(the battery was disconnected) and then I noticed the problem.I will disconnect the battery and start the car for 3 minutes and give it another try.Thanks STL94LT1

James in MD

I will check the temp door positions, as well as trying the battery disconnect process. If there's no success I guess the door motor module is next. I suppose that its a good thing that I have this big hole in my dash where the radio headunit goes. It's out for repair.

LannyL81

Unfortunately having the radio out is not going to help you at all in getting to the air mix door motor.

Access to the motor module is obtained by removing the passenger knee bolster. Then removing two screws and it drops out. The screws are 5.5mm or 7/32 hex head.

I put the HVAC into diagnostic mode and then into the temp door test #31 or #34 (not sure which now). And the display was to show between 100 and 200. By changing the temp between 60 and 90 the motor module would move, but the number on the HVAC display never changed like I was expecting.

Oh well...at least the temp door is moving now so I have heat and defrost, which is a good thing.

Later,
LannyL81

STL94LT1

I did the battery diconnect/HVAC relearn this afternoon, and now I can get heat on any temp setting, not just *90.