chstitans42

So I have a 1999 Corvette, with the dual zone ac/heat. I was having problems with the blow motor not working. I pulled the motor, gave it 12V and it worked, so that isn't the issue. I dropped $170 on a new blower motor resistor, and the blower motor only works at super high. When I push the fan speed buttons, no matter what setting it is at, it either blows super hard, or doesn't blow at all.

SO, do you guys think that it is the control unit? Is there any way to repair this so I don't have to buy a used one?

Any help would be great.
Thanks!

chstitans42

Anybody?

I also hear an audible click from inside mt dash randomly. Sounds like a relay of some sort. Associated? No idea

Tron Z

You can start by checking for voltage at the resistor network. In fan speed position 1, you should see power at pin B, on the yellow wire.
In position 2, you should have power on pin A, which is tan.
Pos 3 - pin D, light blue.
Pos 4 - pin C, purple.
On high speed, pin F, orange.

With power on the orange wire, the resistors are bypassed and a relay inside the resister network energizes (is this the click that you hear?) to supply B+ directly to the fan motor via pin G, red.

You should have ground on pin E, black, at all times.

chstitans42

Thank you so much for the reply. It is weird. Th whole AC system is acting strange. The fan speed button is totally intermittent, sometimes working all speeds, sometimes it gets stuck on a speed, some times nothing at all. I also noticed that the passenger side zone temp changes on the display, but always blows cold air, while the drivers side acts fine (if the blow motor feels like co-operating). Ill be pulling the HVAC codes tomorrow for sure.

The click happens randomly, usually followed by a smaller click right after, whether the ac is on or not.

n8dogg

Sounds like the HVAC head unit may be the problem. They are easy to swap out if you know someone that would be willing to let you try theirs.

chstitans42

that was the next thing I was gonna try. Sadly most of my buddies have c3 and c4 corvettes, and the replacement ones are like $300

n8dogg

I want to say there is a vendor out there who rebuilds these things, possibly Ecklers. eBay may be worth a try to find a used one from a reputable seller.

chstitans42

A little update. Pulled the HVAC codes, and all of them had to do with the actuators... but the weird thing, is that they all had H at the end, meaning they are no longer relevant.

I noticed that the weird clicks and whirrs from the dash come on when the car is running and driving, but also when the key is just turned to accessory. I took the time to pull the HVAC control unit. When I have it unplugged the clicks etc stop and when it is plugged in, they start automatically.

I also ruled out the possibility of the blower motor and or blower motor relay. With the key in accessory, you can hear the pops and clicks from above where the blower motor mounts. When un-plugged (both the motor and relay) the pops and clicks continue.

My next step will be buying another HVAC unit and seeing if it solves the problem!

chstitans42

The only other issue I could see is a problem between the HVAC control and the blower motor. In other words wiring. The only other thing it could be is that I added the sport seats to my car (originally came with the base seats), and had to run power wires to the passenger side fuse box. I used a harness out of another 99 vette. Just plugged in the wires. I dont think that would make a difference but I thought I would just mention it...

$$$frumnuttin'

adding power seats could be related because your PCM is not programmed for that option...who knows if there is a connection, but anything is possible when it comes to the electronics on this car. I would definitely try out a known good hvac controller...used ones sell for around $100....just try someone's unit here on the forum in your neighborhood...it's a 5 minute job to get it all set up.

chstitans42

So, as I am not versed very well on these car's electronics... How would adding a power seat wire to the correct place in the fuse box mess with the ac system? I know people have done these swaps before, so is there anyone who has correct instructions on how to do it? and I thought it was all plug and play...

chstitans42

So I disconnected the newly added power seat, first at the seat, and then at the fuse box. I tested the HVAC controller each time, and no change, the noises are still there. Is it possible I have fried the PCM with adding the extra two power lines? I still think the HVAC controller is to blame...

$$$frumnuttin'

you are probably right, but when I had trouble with my controller (would not light up until after car was warmed up) it fixed itself when I had the PCM reflashed for other problems...it's all about the proper voltage.

chstitans42

Well to rule that out, how do you reflash the PCM? dont tell me the dealer has to do this...

$$$frumnuttin'

best to go to a tuner shop...that way if you have a non-stock tune they can retain your horsepower settings....something the dealer cannot do for you. If your car is stock then the dealer or the tuner shop can reflash your PCM to match your coded options on the car. I hope I am not sending you on a wild goose chase here, but that is what I went through with my car this summer. I bought a rebuilt PCM for other problems and it also solved a number of electronic issues I was having with the car, so just giving you some possible leads. I knew I was in trouble with the AC controller when I switched it out for a good one I had as a spare....the odds of both of them being bad were a million to one and led me to having a shop find the gremlins.

chstitans42

What about the blower motor itself? How prone are these to going nuts? I know mine makes noises, maybe it is on its way out?

Tron Z

For HVAC clicking noises and temperature discrepancies, you may want to have a look at this post:
http://forums.corvetteforum.com/c5-t...actuators.html

davidsdailey

Hello - Did you ever figure out the issue....I am having the same exact issue with my 1997.....driving me crazy.... Call or text anytime if easier 732-330-3319 Thanks Dave

Vetteman Jack

Moved to C5 Tech.