We just got done replacing BOTH temp door actuators on my son's '98 Coupe. It has dual-zone HVAC and both actuators had broken gears (It gets REAL hot here in Phoenix!!). We also replaced the electronic controller and everything appears to be working perfectly. We can watch both temp control doors move and calibrate themselves and all of the vacuum doors seem to be operating properly. That said.........

We now get 88 degree air on the driver's side and 53 degree air on the passenger side. Both temp control doors are in the same position and they will move to the "Heat" position independently under control of the electronic controller.

Any suggestions???

Please be aware that both actuators are brand spankin' new from the dealer and the controller is a rebuilt from Digital Dashes. Like I said....We can watch the doors move into the correct positions. We still have the dash removed. We just can't figure out where the heat is coming from. After almost $600 in parts and about 8 hours labor, we are about ready to disconnect and loop the heater hoses to get rid of the heat. It's supposed to hit 100 degrees in the next two days here.

Any help would be GREATLY appreciated.

 

If it were me,, I would remove the actuators and MANUALLY position the dampers so that it blows ALL cold air. That way you will know for certain what position the doors need to be in to get cold air and that you can get cold air. Then you will have a better idea what is happening that isnt correct.

 

You can try to reset/clear the HVAC codes....try it several times. Not guaranteed to work but we see this and more often than not it will (at least for a while) at least get you to all cold both sides. The acuators try to calibrate. Also try & check for good vacume at the unit, you may have a vac leak. Good Luck! (the heater core bypass will work as well).

 

YES!!! EXCELLENT recommendation! The HVAC system will NOT work properly when a DTC is set!! Clear the DTC and see if that makes a difference,

BC

 

I have read other threads stating that when the R134 is low the drivers side gets the warm air and passenger side gets what cold air is left. I am in Glendale AZ and have 3 used actuators you are welcome to try. My son and I just did the same process for my 2000. I put a control unit from a 2001 in my car as they are supposed to be a little more actuator friendly. Shoot me a pm if you want to try any of these actuators.

David in Glendale

 

that sux dude hope you can figure it out

 

I'm sorry. I should have stated in my original post that the temp actuator doors are in the proper position. We can see them since the dash is removed. I should also have said that there are absolutely NO codes set for anything in the car.

Is there a vacuum door that controls the heat? I have the factory manuals and there is no mention of any heater control valve or vacuum door that I can find.

We are definitely NOT going to put the dash back in until this thing is working perfectly! We just cannot figure out what could be wrong. The system pressures are right where they should be ( I have gauges) and with the passenger side temp at 53 degrees at the center vent, everything seems fine. The outside temperature was over 90 ambient with the display showing 114 at the time we took the temp reading at the vents. This is well within GMs recommeded limits.

I appreciate the offer for the actuators, but we just replaced both of them AND the controller. Everything seems to be functioning fine. We just can't seem to shut off the heat.

 

Especially if you are NOT getting any codes relating to the HVAC system. It sounds like you have fixed your actuator problem, but might be low on freon. I'm pretty sure Autozone will check your freon level for no charge. That would be my next step.

Edit - Just read your reply above. Are you sure your guages are reading correctly? With no codes, that sounds to me like your actuators are doing everything they are supposed to be doing. I still have to say I recommend a second opinion on the freon level.

 

Could it be that little interior air temp sensor, just to the left of the ignition switch, has gone bad? I'm asking, hoping others might chip in who are a little more knowledgeable in this area.

David in AZ

 

This is the first I've heard about these kinds of issues... what are they symptoms? How do you test? Turn on AC then turn dual zone side to hot and see if it gets hotter?

 

I'm about 4 bolts away from pulling the entire dash out of this thing!

I just pulled the new actuator on the driver's side and moved the air valve manually. It is definitely seating properly. The vacuum actuators are all working normally and all of the air valves are moving to the correct position.

I know that the freon charge is OK. My gauges cost $250.00 and everything is reading normal. I don't have a lot of experience with ATC systems, but used to install and repair A/C units on new Toyotas.

Thanks again David for the suggestion. I pulled the cabin temp sensor and checked it with an Ohm meter. The reading is well within the parameters in the factory manual for the current ambient temp.

It is currently 82 degrees ambient here in the Valley of the Sun and I have 46 degree air out of the passenger side vent. I still have over 90 degree air out of the driver's side vent and the car is not even up to full operating temperature.

I WILL find out what is wrong here and report back. This thing may never run down the road again, but it is damn sure going to have cold air blowing out of all of its vents. Thank God and Chevy for those factory manuals!!

Thanks for all of the suggestions. I appreciate the help and support.

 

We pulled everything apart (again) and inspected it for signs of wear, damage, etc. We found nothing wrong. We pulled the battery and battery tray to look for signs of corrosion. There was none. We ran a complete diagnostic vacuum check of all of the lines and actuators following the factory manual and everything was fine. We watched as the new temp actuators calibrated themselves to the new controller several times without a hitch.

We checked the DTC and there are no codes set for anything! We do take good care of this car, but I would have expected at least one historical code, but there were none on any of the systems.

We reassembled the car and started it up. With everything set to its coldest settings, here were our final results:

Driver's side temp. - 88 degrees at the center vent

Passenger's side temp. - 52 degrees at the center vent

Ambient temp. -98 degrees

This is beyond my comprehension. We are going to pull the heater hoses and loop them. It's not the proper solution, but it's just getting too hot to mess with this anymore.

If anyone comes up with a solution, I would be VERY interested to hear about it. We have done everything that we know to do.

 

.....Wow, Im going to check my R-134a level, no codes, just warmer air drivers side than pasenger...

 

Can't hurt to pull the two HVAC fuses in the passenger side footwell fusebox. I believe they are number 18 and 27. That will reset the actuators and it should also reset the control unit if I have this figured correctly. Live them out a few minutes then pop them back in and fire up the car and the a/c. It is worth a shot.

Being that it is your son's car I guess you ride on the passenger side.

Good luck, keep us posted.

David in Glendale

 

I really do appreciate all of the suggestions.

Actually, you really only need to pull fuse #27 to recalibrate the system. We have done that several times and everything calibrates perfectly just like the book describes. Then, just to make sure, we even disconnected the battery a couple of times (once for about an hour) just to see if that made a difference (it didn't). I even had the top of the HVAC box off today just so I could inspect the inside of the box for cracks or blockages (there were none). I also pulled both temp conrol motors and operated the temp doors by hand with no improvement.

Like I said above....I am just going to loop the heater hoses for now to get my son through the summer while I do some more research. If I haven't found a definitive answer by this fall I will pull out the entire HVAC unit from under the dash and put it on the bench. This thing will NOT win!!

These factory manuals were worth every penny that I paid for them. This would have been a big mess without them. They may not have the answer to my problem, but they sure have saved us a lot of time while we are looking.

Thanks again for all of the suggestions. If you guys think of anything else, PLEASE let me know. I am willing to try anything.

 

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 and 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 though it makes no sense to me since there is one common evaporator. 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

 

Wow, good call by David in Glendale about the refrigerant! I don't need to use my AC too often, but this is good info to know.

 

EXCELLENT POST and SURPURB info!!!!!!!!! Well done!! you have significantly contributed to resolving this problem for others!!

BC

 

using those reference charts to determine ac pressures isnt always accurate. latent heat has a much larger effect on pressures than does just outside temps. on a relatively humid 80 degree day i normally see 250ish high side readings and mid40s on the low side depending on the vehicle im working on. another thing to note is that the compressors used in cars now are typically variable displacement which can have a significant effect on the high side pressures

 

That 98 never stood a chance to win this battle against 2Big2Fit. Highs in the 100's for the next week, who cares.

David in Glendale