I just bought my first Vette 3 weeks ago (89 Coupe). It runs great. A/C is ice cold, no problems. I'm running to the Ice Cream store with my daughter tonight, and decide I want to see if turning on the heater will drop my Coolant temp at all. It was running 210. I turn on the heater, and it drops to 195. I go to turn the A/C back on and nothing but HOT air will keep coming. Turn it off, turn it on. Stop and restart. Nothing! Still hot friggen air all the time. The compressor is turning, the Condenser is dumping water as normal. Its like the ac is working, but the heat won't stop flowing into the fan. Any ideas?

 

Check your heater water valve. It may be stuck open.

 

I haven't gotten the shop manual that I ordered yet, so could you point me in the right direction to find that sucker!

 

His '89 doesn't have a heater valve. Either it has a vacuum problem which is causing the door under the passenger side dash to open and close properly, or you have a short in your Electronic A/C panel. I can tell you how to get to the door if you like, but it is not an easy job, let me know if you want the instructions.

 

My vote is for the blender door. It is not vacuum controlled, but controlled by a little motor under the passenger side hush panel. You can check the operation by doing the following

Open the hood and move to the passenger side where the A/C lines go into the evaporator housing. On top of that housing there is a harness that plugs in. There are 3 7mm screws that you need to remove and then pull out that harness and controller. Grab a flashlight and look down in the hole at the door inside there. Have someone turn on the car and switch the temperature settings from 60-90 on the temperature gauge. If the door doesn't move, grab a long screwdriver and stick it in there and *GENTLY* see if you can move the door with the screwdriver. If you can, the little white plastic clip that sits atop the motor under the hush panel is broken. If you can't I would say that the motor that controls the linkage is bad.

If you need instructions on how to replace that peice, I can give you those as well.

 

I will give that a try tonight. Thanks for all the advice. I will let you know how it goes!

 

[QUOTE=88vettelover]My vote is for the blender door. It is not vacuum controlled, but controlled by a little motor under the passenger side hush panel. You can check the operation by doing the following

Open the hood and move to the passenger side where the A/C lines go into the evaporator housing. On top of that housing there is a harness that plugs in. There are 3 7mm screws that you need to remove and then pull out that harness and controller. Grab a flashlight and look down in the hole at the door inside there. Have someone turn on the car and switch the temperature settings from 60-90 on the temperature gauge. If the door doesn't move, grab a long screwdriver and stick it in there and *GENTLY* see if you can move the door with the screwdriver. If you can, the little white plastic clip that sits atop the motor under the hush panel is broken. If you can't I would say that the motor that controls the linkage is bad.

Amen,
That is what was wrong with mine, Hot are all the time until you push that rod back and forth. The plastic clip was broken. Fixed the problem with a new clip and bingo. Took longer to get the passenger seat out and Ecm out then to pop a new clip in.

 

Hey Talmadge,
I have the same problem with my A/C unit, 89 'vert. Everything seems to work ok except the blender door in the evap housing is not blocking off the heater core.
I have my passenger seat out and am about to remove the ECM; any tips on what to do and not do so that I don't damage the ECM.

 

I was referring to the blender door as well. Mine is also an electrical motor, but is in fact controlled by a vacuum line

 

Are we talking about the same thing? There are 2 doors underneath by the passenger side hush panel. One door has an orange vacuum line going to it, that is not the blender door. The Blender door has an electronic motor that pivots the door open and closed.

Whoever posted about removing the ECM, unhook the battery, and then just drop down the ECM (I think it's 2 10mm bolts.) I didn't unplug mine, just dropped it down and moved it out of my way. Then you have to do some feeling around for each of the 7mm screws that hold the motor to the heater core box. One is on each side. Once you get those out you should be able to figure the rest out. Clip sits in the little arm on top of the mottor, and then clips onto the threaded rod to the Blender door. After I got the motor out, I plugged it in and made sure the arm still moved when I switched the temp from 60-90. It did, so I only replaced the clip.

Good luck!!

 

Sorry, I didn't mean to highjack your post; got caught up in trying to fix the same problem you're having with your A/C that I'm having with mine. Hopefully we can both benefit.

Anyway, guys, on my C68 system, I did find the motor and linkage that operates the blender door, (its right in front of the ECM) and the plastic clip looks to be ok. I tried to move the rod but it wouldn't; is it supposed to? I figure it's not supposed to since you're trying to move the linkage against the motor's drive.

I took the Programmer down and looked at the circuit board. The 2 resistors that have been discussed before in a lot of other posts look like they did get hot as the area around them looks burnt. The solder joints were bad so I resoldered them. The resistors themselves looked ok, and read about 119 ohms each, but I'm not sure of the values. The color bands in order are: brown; orange; yellow(or gold); the resistors are both light blue in color. From my Navy days, brown=1; orange=3, and the yellow or gold band is the multiplier. If it's yellow, than its 10k; if gold, its divide by 10. Need help here!!!!!!

BTW, after getting a temperature set point via the Controller, what actually provides the power to operate the blend door? Is it the Programmer?

Thanks, in advance, guys.

 

Your instructions worked great. Once I was able to giggle that flap a little it started moving freely. Went through a couple cycles of hot/cold and it seems to be working properly now. I guess it just needed a little excersize!

 

Just some feedback on the problem that I had...........

Picked up a new Programmer from the dealer and installed it this afternoon. I now have temp. control where before all I could get out of my vents was hot air even though my a/c was putting out cold air. The old Programmer was not supplying power to the motor that actuates the temp. door inside the evaporator housing.

Before installation, I compared the two resistors to the old ones that I wasn't sure of their resistance values ; they looked the same, but on the new ones the color bands were easier to distinguish: brown, red, brown which reads out to 120 ohms. The tolerance was 5%.

Thanks to all who gave their inputs!