Sierra/Silverado HVAC Actuator (Blower on Defrost Only)

[hanson]

Takes me awhile to get around to some of my auto repairs but this one is getting old now.

My truck is a 99 GMC Sierra Extended Cab 5.3l 4x4 (New Body Style).

First I lost fan speeds 1,2 and 3. Was educated here as to what a Blower Motor Resistor is and proceeded to get that swapped out. All good. Still have all my fan speeds.

About the time I got that fixed, I noticed I had defrost only. No matter which position I set it at (floor, panel, defrost, etc...), it always comes out the defrost. Now my other problem was my heat is all or nothing. Honestly don't know if all this stuff is related or what the heck happened.

Anyway, the diagnosis in this forum was a blend door actuator when I asked which was quite awhile ago believe it or not. Now I have no clue where this thing is but I decided to replace my cabin air filters today (which have never been done... didn't even know I had them!!). Got the plastic shroud pulled off, found the cover for the cabin filters, my oh my were they packed with dirt and leaves and stuff. Wow!!

So while I was under there, I located a part that sure seamed to look like an actuator. Did a little searching on the net and you betcha, we got a bingo! Called around and found a NAPA that had one and popped that in with the new cabin filters. Learned the hard way you don't plug the wires into the actuator until you have it in position. Had to take the cover off and try to rotate the gears into position. Hope I didn't screw that up it seams to have worked. I now have control of cool/hot function again. So apparently this actuator controls the hot/cool mix, I seam to have full control over that again but still not the defrost/floor/panel controls.

Little more internet searching led me to yet ANOTHER actuator located up under the dash on the drivers side. Now this seams to be the one that will fix my problem with the defrost/floor/panel controls.

Anyone here changed this out and any tips? I've got some of the plastic ducting for the floor out of the way to give me room but it sure looks tight up there. I'm not going to attempt it until I have the new part so I've got some game planning time.

Help! Help!

[Jeremy airjer W]

Before you replace it try doing a recalibration.

-Turn the key off

-Pull the HVAC fuse in the underhood fuseblock.

-Wait at least 60 seconds.

-Reinstall the fuse.

-Start the vehicle.

you should hear the HVAC running through a couple of self test. Wait for about a minute and then see if the HVAC will switch modes. Try it a couple of times before you decidfe to replace the mode actuator.

[hanson]

I tried a few different things this afternoon... disconnected the battery, hooked it up again and then started the engine. Tried pulling the fuses as well. Just to be sure, I went out and did what you just posted Airjer and it didn't seam to do anything. I honestly don't hear anything "happening" as far as a calibration goes after I start the truck... no clicking or parts moving or anything that would tell me something was happening.

I'm thinking I need to replace it but it sure doesn't look like much fun.

[jwhjr]

The driver side one is actually pretty easy to replace. I replaced it in my 04 a few months back and it took about a half hour tops. I would not want to replace the one on the passenger side in my truck, you have to pull the dash pretty much all the way apart from the looks of it.

[jwhjr]

FYI - In my truck at least, both the driver and passenger side actuators are the same part. When I replaced the driver side one, I pulled the old one apart to see if I had a cracked gear in it (I didn't). Here's a pic of the inside of one:

[hanson]

I just ordered the part this morning. My truck (99 GMC Sierra) has 2 different part numbers for the different actuators. Seams like a lot of the parts stores have the temp control actuator in stock but the hvac mode actuator has been tougher to find.

My truck has manual controls for the front and not the newer digital driver/passenger controls found in a lot of the mid 2000s GM vehicles. Probably a makes a difference with what parts do what.

[hanson]

To follow up with previous posts here... I'm back in business!!

Somewhat nice day and a little spare time so I tackled the HVAC Mode Actuator this afternoon.

Really not that bad of a job although pay attention to plastic cam mechanism with the slots in it and how that indexes the white gear that operates the door. When I got the actuator loose, everything else got out of alignment so I had to do some thinking about how it operated. I guessed right and its working now.

This time when I turned the key, I waited a bit and heard all the actuators calibrating and doing their thing.

So if anyone else runs into this on an early 2000 Sierra/Silverado, here's the game plan:

1) No fan speed or fan operates on 4 & 5 only = Blower Motor Resistor

2) No hot/cold adjustment, in my case always blew hot = Temp Door Actuator (Passenger side below dash)

3) Stuck on Defrost or can't switch from defrost to floor to panel = HVAC Mode Actuator (Driver side up under dash)

Blower Motor Resistor and Temp Door Actuator are pretty easy, the HVAC Mode Actuator is not too bad if you pay attention. I've had to do all 3 now on a 235,000 mile 99 Sierra.

While you are under there, change your cabin air filters as well.

I cringe to think what a dealership would have charged for this. All 3 parts with cabin filters I picked up for $150-160 thereabouts.