HVAC Issues

I have been having issues with my HVAC system, seeming to stem from the control unit. I posted in another topic about this.

My old control head unit started, suddenly, displaying all temps as negative temperatures a few weeks ago. Soon after that, I turned my car on and a loud, ear-piercing screech of a beep started coming from the unit from when I turned the car on until when I turn it off. It is still doing this. I had the head checked out and a friend told me that it was internally bad. So, I purchased another used one.

I just plugged the new-to-me used control unit in and this one is giving off the beep and displaying negative temps as well... same symptoms. I am guessing this may be a wiring issue? I have no idea. I ordered a FSM set about 2 weeks ago and it still hasn't shipped, otherwise I'd look into the issue there. Does anybody have any suggestions? It is the worst when your windows stop working and your HVAC has to be taken out and we already have 70+ degree days this early in the year.

I would try unplugging the outside ambient temperature sensor. it's worth a shot, and easy to do.

also check the wiring harness to the steering wheel controls (a quick visual for now) you will have to pull the kick panel to do this but it is not a big deal.

Hey guys, I finally had somebody take a look at this issue for me, and thank god, because it would have been a lot of searching until I found the problem. I took my 98 to a really well-renowned auto center that has looked at electrical problems in my car before and this is what they did:

They inspected (apparently for a while, according to the mechanic) and found that there is a programmer for the hvac control unit that was back-feeding power to the unit and causing the noise and related issues. They removed this "programmer" (located under the glove box) and cleaned the unit. After reinstalling, the noise was gone and the hvac unit worked properly. I also tested my other unit and it is working just fine too, whereas before both of them made that eardrum-bursting noise.

The guy that I talked to there said that they have never seen a problem with the programmer that they were talking about before, and said the mechanics had no idea why cleaning it would make the unit work properly. They said that the programmer may have to be replaced down the road, as that is the root of the problem.

I hope this helps anybody else who is / will have this B.S. happen to them!

ZEP wrote:

Hey guys, I finally had somebody take a look at this issue for me, and thank god, because it would have been a lot of searching until I found the problem. I took my 98 to a really well-renowned auto center that has looked at electrical problems in my car before and this is what they did:

They inspected (apparently for a while, according to the mechanic) and found that there is a programmer for the hvac control unit that was back-feeding power to the unit and causing the noise and related issues. They removed this "programmer" (located under the glove box) and cleaned the unit. After reinstalling, the noise was gone and the hvac unit worked properly. I also tested my other unit and it is working just fine too, whereas before both of them made that eardrum-bursting noise.

The guy that I talked to there said that they have never seen a problem with the programmer that they were talking about before, and said the mechanics had no idea why cleaning it would make the unit work properly. They said that the programmer may have to be replaced down the road, as that is the root of the problem.

I hope this helps anybody else who is / will have this B.S. happen to them!

Why cleaning the unit would work - let's say your car was in an accident or flooded - just saying - the silt can mess things up, even getting into connectors and making electrical continuity between circuits where there should be none at all. Cleaning the unit will get rid of the likelihood that smarm in a connector is shorting something out.

Big Kudos to the auto center, although I kinda wonder what electrical drama your car has been in for before.

Inspecting for dirty connectors is part of what I mean when I say Check The Wiring.

My car has not been in an accident of any caliber above hitting the curb a few times, and has never been flooded (as far as I know, I'm not the original owner), but I know of course residue and silt/debris build up over time and may have had something to do with all of this. Now I am getting a sort of rubbing sound coming from under the glove box when my A/C is on. Seems like everything is working fine, but I hear a rubbing sound as if some kind of component is opening and closing repeatedly. It then stops for a while and comes back. I am wondering if this is the programmer? I will have time in a few days to investigate.

As far as electrical drama, I haven't had much, though each issue has led to a really annoying problem. A wire leading from under the coil packs was damaged inside of its insulation, which resulted in hesitation when accelerating. Fixing that solved that problem. And of course, I found that a mildly loose connection for the positive battery terminal in my engine bay caused my car not to start. Other than that, I have no other record of anything else electrical-related. Now I see that wiring is half the battle with these newer cars!

ZEP wrote:

Now I am getting a sort of rubbing sound coming from under the glove box when my A/C is on. Seems like everything is working fine, but I hear a rubbing sound as if some kind of component is opening and closing repeatedly. It then stops for a while and comes back.

This sounds like an actuator module for a blend door. There are several under there. Next time you hear it cycling repeatedly, if you have some time to mess with it, take the climate control out of Auto and move the temp up and down, the air from floor to vents to dash and see if you can tell what triggers the sound. I describe it as crickets under the dash... but it tends to only act like that in Auto mode.

Awesome, Derek, thanks. I'll take a look when I have some free time. I never have the climate control on Auto though, so maybe the sound I'm talking about isn't the crickets you describe (it sounds more like creaking, like a door hinge would or w/e). Anyway, I'll get to the bottom of it!

Even though the HVAC isn't on Auto, the temperature control is always 'Auto' unless you are set at 60 or 90. Even at 90 you can still reach 90 in the cabin and the blend doors start to regulate. But as a test moving the temp setting to 90 would pretty much ensure full heat, and likewise for 60 to put the blend at full cold) Sometimes the passenger comfort setting will take over. I forget if you push Auto twice to reset the pass. comfort setting or hold down auto or something, or maybe that's a different vehicle I'm thinking of. But make sure the pass. side is set to neutral while you are testing.