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Discussion Starter #1
We just got done replacing BOTH temp control actuators and the digital HVAC control on my son's '98 Coupe. The actuators both calibrate fine and we can see the doors move (the dash has been removed). However, we are still getting hot (88 degree) air from the driver's side vent while we are getting cold (53 degree) air from the passenger side vent.

We have checked everything including the freon charge (I have gauges) and everything seems to be working correctly. It is supposed to get to 100 degrees here in the next couple of days. Any help would be appreciated.

Please Note: There are absolutely NO codes set for anything in the car. We had error codes for the actuators, but they are now gone since both actuators were replaced. Both actuators had broken gears and were replaced with brand spankin' new ones from the deaer ($240.00 each).
 

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Discussion Starter #3
We pulled the entire dash apart today and inspected the entire HVAC system. We disassembled everything (motors, vacuum motors, air doors, etc.) and inspected it for signs of wear or deterioration. We found absolutely nothing wrong! We watched as the new steppers calibrated themselves with the new controller several times. Everything went off without a hitch. We even pulled the battery and battery tray to look for corrosion. We also ran a complete vacuum system check following the procedures lined out in the factory manuals that we have. Everything was perfect.

In the end we had 88 degree air on the driver's side and 53 degree air on the passenger's side with an ambient reading of 98 degrees and a VERY heavy sunload coming through the windshield. Both temp doors were locked in the cooling only position.

This is beyond my comprehension. There are NO codes set in the DTC. Not one for anything. Not even any historical codes. You would think that there would be at least one problem with a car that's 9 years old. However, we are very proactive about maintenance.

It's just getting too hot to mess with this anymore. We are going to pull the heater hoses and loop them back to bypass the heater core. It's not right, but it will get the job done until we can find out how to repair it correctly.

Any fresh ideas would still be appreciated.
 

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DC PIT CREW BOSS
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Does the car have dual air or single air? Did you replace the HVAC control with a dual air or single air setting one? Now for the stupid question. If it is dual air is one set cold and the other side set hot? Sorry, I had to ask. The system is supposed to allow a 3* variance one way or another. Maybe the controller is bad and allowing a greater variation

A few things to check are the recirculating air door and the air temperature door to make sure they are operating correctly. Also check the inside air temperature sensor and the sunload sensor to make sure they ares working correctly and supplying the correct voltage to the system.

Just a few ideas
 

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Discussion Starter #5
Thanks to The Torch

Yep! Been there done all of that. Not trying to be a smart a**. I'm just VERY frustrated at this point.

It's a dual zone system. We just replaced both actuators and have checked for proper calibration and operation with the rebuilt controller. The Ohm meter verified that the cabin temp sensor is right on the money with the specs from the factory manual based on ambient temperature.

The main (driver) setting is working as the master control and the passenger control is modulating that side properly based on the driver side setting. I even removed the temp control motors and operated the baffles manually with no improvement. This whole thing is like an episode of the Twilight Zone. I had this thing torn down so completely today that I actually removed the top of the HVAC box to verify that all of the linkages and shafts were working correctly internally and that there was no cracking or blockage in the main air box. If something is still not right, I don't know what it could be. I was about 4 bolts and a couple of freon connections away from having a bare firewall inside this car. I did a visual on EVERYTHING. I even ran a complete diagnostic on all of the vacuum systems (lines and actuators) as outlined in the factory manual.

If I EVER do find out what is causing this problem, I am going to take an unbelievable amount of pictures. I am going to bypass the heater core for now by looping the heater hoses. That will get my son through the hot summer months here. Then this fall, if I haven't found a definitive answer, I WILL pull out the entire HVAC unit and put it on the bench. We really like this car and I refuse to go down without a fight.

Thanks for the help. Let me know if anyone has any more ideas. They are all appreciated.
 

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DC PIT CREW BOSS
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Going after straws here, You did recalibrate the HVAC module when you installed it, didn't you? Can you manually close the heater door, does that affect the hot air flow? IT should eliminate it. Not much left except the routing of the ducting. Sorry I can't be more help

Worst come to worse, an old fix was to install a valve in the line rather than bypassing the heater core, then if you needed heat you only had to open the valve rather than re-routing the hoses



"You're traveling through another dimension, a dimension not only of sight and sound but of mind; a journey into a wondrous land whose boundaries are that of imagination. That's the signpost up ahead - your next stop, the Twilight Zone!"

:laughing:
 

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Discussion Starter #7
We recalibrated everything several times. We even closed the temp control doors manually with no improvement. The air flow diagram in the factory manual shows that that should cure the problem. The air comes from the blower through the evaporator and then through the heater core. The temp control doors should route the air around the heater core when they are in the closed (down) position. This is working on the passenger side, but not the driver's side. We visually confirmed that the doors were moving to the proper positions. I guess I'm just too "Old School". In a small cabin space like this Vette, just a plain old single zone A/C would be fine. However, you can't always get what you want when you are buying a used vehicle like my son did.

I also thought about putting in a valve, but I was concerned about interrupting the flow through the entire system. The heater hoses route back to the overflow tank. I don't want to make another problem for myself. I was thinking of putting in an "H" block with a vacuum valve like the older Chryslers and Dodges used. When that valve is closed, the water automatically gets looped through the built-in crossover.

Again...I appreciate your thoughts.
 

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Discussion Starter #8
OK. You can all laugh now.

I went over EVERYTHING one more time and the problem is fixed. You won't believe what I found! (Well, maybe you will).

The first thing that I found was that sitting in one place idling for a long time causes the entire tunnel area to heat up tremedously. This pushes the driver's side temp up. When I took the car for a drive, I actually got the air at the driver's side vents to drop from 88 degrees to 62 degrees (Still not good enough).

Then I went over the specs in the factory manual and noted that the recommended system pressures seemed a bit low compared to other charts that I had for ambient air and humidity.

The factory manual was calling for 27 psi/ low side an 135 psi/ high side at 1,000 RPM. I finally decided that I had nothing else to lose (but a compressor) and added more R-134a to raise the pressures to about 30 psi/low side and 250 psi/high side. Ambient is about 82 degrees this morning.

I now have 42 degrees at the center vent on the driver's side and 40 degrees at the left vent on the passenger's side of the dash. The factory manual calls for 40 degrees on a perfect system.

Everything is running fine with no unusual noises. I should have gone with my gut feeling about those pressures from the beginning. Anyway......the thing about low freon causing high temps on the driver's side is right on the money. The temp control doors were completely shot and that just added to the problem. On the good side, I now know this HVAC system inside and out. That is important here in the desert.

Thanks to everyone for their help.

--Al
 

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Glad to here it worked out.:thumbsup:
 
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