Mode Actuator Problem?

ROBBSRACINGENGINES · May 30, 2010

Hi guys first post. Been lurking a while but time to post my own question. I searched first and found a bunch of actuator posts but couldnt find one with my exact problem.

I have a 1999 GMC 1500 Sierra. The other day the AC stopped blowing from the vents and would only come out the defroster. I found the mode actuator and watched it while I moved the selector and it never moved no matter where I put the selector. I went and bought a new actuator and plugged it in to see if it moved and it did. I installed it and the problem changed but wasnt fixed. I tried reseting by pulling the HVAC 1 fuse and that didnt help so I tried disconnecting the battery and that didnt work. I started looking around here and found that I should NOT have plugged it in before mounting it. I took it back to the auto parts store and got another one. This time I installed it BEFORE I plugged it in. Now when I put the mode selector on vent it comes out the defroster. When I put it on defrost it comes out the vent and when I put it on floor it doesnt come out anywhere. What the heck is going on here ? Thanks for your help.

ROBBSRACINGENGINES · June 1, 2010

Anyone? Please.

serickson28 · June 18, 2010

Anyone? Please.

Did you ever get this resolved? Sounds like the same problem we are having with our Silverado, the dealership told us that it was the control panel.

safeman · June 23, 2010

Hi

Try this actuator recalibration procedure.

With the ignition switch in the on position, remove the HVAC/ECAS fuse for a minimum of 10 seconds. This fuse is located in the under hood fuse/relay box.

Re-install the HVAC/ECAS fuse.

Start the vehicle.

Wait 40 seconds for the HVAC control module to self-calibrate

Try this..... it SHOULD work

ROBBSRACINGENGINES · March 11, 2013

So its been 3 years and I still have this problem. It hasnt bothered me until recently when I got sick of having cold feet. Just to re-state whats happening when I put the mode selector on vent it comes out the defrost. When I put it on defrost it comes out the vent. I can never get it to come out on the floor no matter where I put it. I have replaced the actuator again. Still the same. I have tried every recalibration procedure I have seen on the net and still nothing. I took it to th GM dealer to see if they could calibrate it with a Tech2 and they told me my truck is to old for that to work. When I watch the actuator move while turning the mode selector it seems to turn the wrong way. In other words when I turn the mode selector to defrost the actuator moves ccw which moves the cam arm to the vent position. It never stops in the middle which would be the floor setting. Im stumped again.

bossier62guy · March 11, 2013

Here's a little troubleshooting info for you. If I can help w/ any more info let me know.

modeact.pdf

gmtech4 · March 11, 2013

how about diagnosing the code in the HVAC module ?????

ROBBSRACINGENGINES · March 12, 2013

I tried following the troubleshooting tree. Steps 3 and 4 are yes. When i get to step 5 it gets messed up. When i measure the voltage from the control circuit of the mode door motor to a good ground and operate the mode control switch things get wierd. On the defrost setting I get 0 voltage and as I turn it CCW towards Vent it stays at zero going past the floor setting all the way untill just before vent when it jumps rite to 4.98 volts. So zero volts on defrost is correct but 4.9 volts on the floor setting is incorrect. It doesnt say what to do if that happens. lol. I had the opportunity to try a junkyard HVAC control today so I did and that didnt change anything either. Same problem.

I search through all the Mode Actuator threads here and found 1 where the same exact thing happened to them after changing the actuator but no one ever came up with answere for them either.

Any thoughts?

gmtech4 · March 12, 2013

the code number is ?

ROBBSRACINGENGINES · March 12, 2013

What code number are you refering to? Something I can check with a basic scan tool?

bossier62guy · March 12, 2013

It says to continue to step 6 if you did not get the desired results. Keep going with it. I can send you the schematics if you need them as well.

I don't think you can get HVAC codes w/ basic scantools.

Just to make sure we're talking apples and apples....this is an 800 series truck?

gmtech4 · March 12, 2013

800 is old body twice removed right ,,,,,,so confused ....lol

OP the code you followed ,what was it ??? i want to look it up

bossier62guy · March 12, 2013

800 is old body twice removed right ,,,,,,so confused ....lol

OP the code you followed ,what was it ??? i want to look it up

Yea Rob that would be a NBS 99.....ridiculous I know LOL

ROBBSRACINGENGINES · March 12, 2013

Im confused here. The body style is the newer one. Most everything I buy for it has to be for a 2000.

bossier62guy · March 12, 2013

Im confused here. The body style is the newer one. Most everything I buy for it has to be for a 2000.

It's an 800 series truck then....there were also 400 series truck built during the same time. Obviously different wiring diagrams, etc. I should have known from the 99 1500 Sierra though.