I previously ran a post about my heater core woes. Received several messages all good but still don't think I'm where I need to be on trouble shooting this problem. Had AC working it's R12 system. Had competent mechanic replace my heater core.
All I get now when driving is heat. Took it to same shop who checked out my system and renewed R12 and found that it all leaked out even after a sniffer leak detector showed no leaks. The car is an 89' so things happen they said they probably should pump down put in R134 with leak detector and go from there. So now I know why I don't have AC but I can cycle compressor so I know ac system working just not charged enough to blow cold air. Second is the heat /hot air problem. I can hear vacuum switches working shifting air from defrost to floor. I can switch to ECON but with the heater core hoses connected get hot air out the ducts. When I shut off everything I still get hot air coming down on my legs but not as bad because there's no blower activated. I know these cars run hot in the cabin but I don't want to drive the car in 90 degree weather it just wilts me.

I had buddy pull panel and look at blend door. He said rod was connected but no matter whether I put the temp control at 64 or 74 the blend door didn't move. Buddy feels I should have ac fixed then see if there's movement in blend door.

Right now I'm frustrated to the point where I pulled heater hoses and connected them together so I eliminate the blowing hot air on me condition. Any thoughts.. I'm getting so tired of troubleshooting this and not determining what's wrong that I'm actually thinking of selling car and buying a newer model which my mechanic points out have "other" problems.

 

looking for help any suggestions short of burning the car would be viewed as an act of kindness

 

The blend door actuator in my '86L (electronic a/c control) failed in my car in full heat. I diagnosed it the same way you and your buddy did. I removed it and zip tied the damper to full cool and began searching for the replacement. The plastic gear train grenaded. I found a part number on the gear box on Ebay (not the whole actuator) and swapped it onto my actuator. Crossed fingers and reinstalled. 2 years ago so far still working fine. The complete module is expensive so i tried this first & it worked.

 

Thanks Benny 42. I've researched some more and found that the HVAC Programmer which resides above the gas pedal could be the culprit. Blend door movement is thru actuator but that gets its vacuum from the HVAC programmer.
I think its now down to one of those two. Wardie

 

There are 2 resistors in the vacuum control module that run hot. Even though they look burnt, mine were still good. They just needed to be resoldered.

 

My bet is the programmer (my 88). batee.com rebuilt mine. The blend door motor can also be rebuilt by batee. Programmer is complicated to remove due to the location and the lack of slack in the wires and tubing that connect to the programmer.

 

+1 for checking the programmer. I just had to resolder mine and it was good as new. Just be careful with the plastic clips on the blend door itself, they break very easily (ask me how I know).

 

I agree. The programmer is probably the culprit. If the vents change I would think the vacumn proggammer is OK. I am having same problem.
. From Batee

 

Ok I pulled the blower resistor from the top of the evaporator and I can see the blend door. If I run temp to 90 door is all the way open. If I lower temp to 60 door closes half way.

Now FSM says any time door, actuator or rod disturbed pull negative terminal and wait a second and reconnect. Heater core was recently changed and it was installed correctly. I did that now the blend door won't move at all?? WTF If I ever buy another vette with C68 electronic HVAC I want someone to kick me in the butt!!

Now the door doesn't move at all AFTER the unti recaliberated. Ok I'm stumped any ideas??

I disconnected battery cable should I of pulled AC fuse or something?

 

these many post abot hvac troubles is making me shy away from working on mine, which has your problems, Mine is an 86 and I know at sime point I will have to fix it,

 

Having been through this, the ac/heater programmer controls the air blend door. Question, does the blend door motor still make a noise after the door stops moving while trying to move to the other side? Send both the motor and the programmer to batee.com. That's what I did.

Yes, the C68 unit can be a pain. I tend to think it was a gimmick back in the day. Give me the slides any day. I didn't buy my C4 for the C68. It came with the car.

 

after I disconnected the battery and reconnected like FSM said to do the door doesn't move whereas it moved halfway before? I know theres a cover that you take down to access the HVAC Programmer but how hard is it to get to that press on nut between all those hoses?

 

can U tell me the steps to remove the programmer? How do you get that nut off the center? between the tubes?

 

See the small needle nose pliers in my pic. Put the head in between 2 hoses ( you should have an empty place) and carefully twist it until it breaks. Just don't damage the silicone hoses. When you re-assembly you can use a regular nut. The nut I used fit a 1/4" socket. You just need to tighten by using your hand.

 

Thank You

 

No one to help me there on the press nut. I had to wing it. Good luck. Post a pic of your 89 when you finish.

 

I feel sure this is not your problem. That programmer just works the vents and not the blend door. The main unit is the one that controls the blend door motor which is a separate unit. Go to your manual and look at the diagrams.

 

Ken I sent U a PM

I replaced the C68 main unit in dash with a known used working one. Temps go up and down fine. Vents shift fine. Blend door doesn't move.

If you're saying Blend Door Actuator receives its commands from c68 main unti in dash that unit is working fine.

 

The module that controls the blend door is above the gas pedal with the vacuum hoses. I removed my drivers seat to get to it easier. I took a picture of the vacuum hoses prior to removing.

 

The blend door is moved by a rod connected to a cam atop the Blend Door Motor. Said motor is located under the passenger side dash.
It may be necessary to drop the ECM to see of the motor cam is moving and if it is still connected to the Blend Door rod.
I've had the little plastic connector break off so that rotation of the Blend Door cam could not move the Blend Door rod.