berryj

Well I've been dealing w/ this one for over a year or so w/ my dual zone hvac on my 99 A4. If I keep the temp setting on 60, it blows nice very cold air out the vents and I can change modes and blow it via floor etc no problem like normal. When set at 60 it typically reverts to the closed recirculation mode, but I can switch it to take in fresh air no problem. Using the "auto" switch just makes it turn the blower up to full.
Now here is the problem: If I try to turn the temp setting above 60, lets say to 61 or higher, then the mode switches automatically to floor vent and blows hot air. Then if I manually change that mode to front vents it just blows that hot air out all the vents. Hitting "auto" doesn't help, just continues to blow the same hot air out all vents, just at max output on the blower. If I then turn the temp setting back to 60, then the cold air comes out the front vents (pass/driver both) no problem with the mode switching back to the front vents by itself.

I have no hvac codes on my pcm, ever as I've checked many times over the past year. I've disconnected the battery to "reset" the actuators but that had no effect. This isn't the common complaint of "hot air on one side, cold on the other" type problem which the search turned up.
Also as a trouble shoot, I bought a used hvac contoller and installed it 2 days ago to see if that would cure it, no dice, but only a $100 piece.

Any ideas? I know, it's a weird problem and I'm very grateful that at least I do have very cold a/c if I need it, but just a pain to get freezing and then have to keep turning the a/c off to warm up, then get hot, etc. Wife is annoyed and wants it fixed! Oh, the freon has been filled up many times and that isn't the problem.

Thanks for any input on this one!

AllVette

I would suspect the interior temperature sensor. If the sensor is reporting a cold temperature in the car the system would act as you describe.

berryj

I was wondering as was my friend that the internal temp sensor might be a possibility, but I wasn't sure. I'll go ahead and get one and we'll see. Certainly a cheap and fairly easy thing to replace.

Thanks Allvette for the tip!

2K-C5

SEE: http://forums.corvetteforum.com/show....php?t=1684273

I know this sounds stupid; but the problem is could be your EXTERNAL temp sensor. This is a common problem. Apparently there is some computer logic that will disable the A/C if it thinks it is too cold outside (which it may think if your sensor is bad).

I replaced my and it fixed the problem.

Good Luck.

trussme

It also could be A faulty outside air temp sensor...A bad sensor puts your system in the 60 to 69 degree fault mode. (Takes a 60 degree setting to get the AC on).

GM Part # 10248414 is aprox. $10 from the dealer and just plugs in.

The sensor is located on the right (passenger) side of the car, on the outside of the frame rail in the very front by the headlight.

It is held onto the mounting hole on the frame by a plastic push-in clip.

Just pull the clip out of the hole on the frame, release the plug for the wire (the plug has a release clip, pry up on the clip and the plug will release).

Then just put in the new one and you will be in business - it takes a few minutes of driving for the sensor to start reading the outside temp - you have to be moving.


The sensors are either resistance temperature detectors (RTD's) or Thermistors. The resistance of the sensor changes with the temperature.
If you have any corrosion in any of the associated connectors it will increase the resistance that the climate controls is reading.
The resistance across the two sensor wires could be almost infinity,
in that case your display would read a low temp.

BTW, Once the old sensor is removed, the HVAC defaults to 69degrees, and will let the AC turn on.

bestvettever

Hi, setting the temp dials at 60, bypasses the temp door actuators and allows the air to come into the cabin through only the AC coils and none through the heater coil. If moving the left dial past 60 causes only hot air to come in I would suspect that the actuator doors are either in need of recalibration, or bad. Or the control head is bad, since you said that you got a used control head and it didn't change anything, (assuming that the used one is absolutely known to be a properly working unit), then the doors are in need of recalibration, or replacement. Try the fuse #27 pull, the proper way to do it is to have the key in the on position, set the left dial at 72 and the right dial straight up, pull fuse 27 and wait the full 60 seconds at least, replace fuse and listen for the door recal sounds, if that doesn't work after a few trys, the doors are bad.
Good Luck.

berryj

Thanks guys, I'm going to get on this and see what happens. More to follow...

berryj

Update: I ended up fixing my turnsignal multi switch issue and while doing so I noted my internal temp sensor looking a little bent so I straightened it out. That seemed to fix my a/c problem so far. Later on I did the actuator recal procedure from bestvettever just in case. I did hear the doors moving so all seems good for now. Exterior temp has been accurate so it doesn't seem to be the external temp sensor so far. Thanks to all for this great help!

bestvettever

Hi, thanks for posting back and helping others. Glad it worked out.
Luck To ALL