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2003 chevy trailblazer_ls
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Discussion Starter · #1 ·
Hello all. I am new to this forum, but I belong to a similar forum for Honda Civics. My wife drives a Trailblazer, and I of course inherited the role of "mechanic" when we got married. :)

My first question for you all is about the climate control. When the heat is turned on, it will stay on no matter what. Even if the controls are turned to cold and A/C is turned on it blows hot air. If we pull over and shut the truck off, wait a few seconds, then turn it back on, it works normally again. What is causing this, and is it an easy fix?

My best guess is there is some kind of vacuum control for the damper over the heater core that is malfunctioning. When the car is shut off, it loses vacuum pressure and closes the damper. How close am I here?

Any help you could give me would be much appreciated!
 

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well there are no vacuum hoses behind the doors.
it uses electric motors.
There is a procedure where you pull the Fuse for the AC system...
leave it out for a few minutes- then put it back in--- but do not touch the AC controls.
You will hear some sounds as the motors calibrate/learn their positions.

Hopefully someone can chime in with the exact procedure//
 

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Discussion Starter · #4 ·
Hello again. A little update on the situation....

Drove from Lincoln, NE to Omaha, NE yesterday (about 50 miles) with A/C on and ok. It will still go straight to heat if we mess with the controls, so we just left it on cold.

I had to replace the passenger headlight socket because it was melted. Not sure how or why, but it's fixed now. Anyway, I disconnected the battery while repairing the headlight. Hooked it all up, and now the A/C does not work at all. When the A/C button is pushed, the accumulator gets cold and the clutch on the compressor starts and stops like normal. I'm pretty sure the A/C is working. However, it just blows hot air. Also, I pulled the fuse under the hood for the blower, but if the fan speed control is on 1 through 4, the blower still runs. WTF? If it's on 5 it quits. Does it sound like there is a short somewhere? About a year ago we did have an aftermarket stereo put in, so the whole control panel was taken apart. However, this problem didn't start until a few months ago.

Also....

Pull fuse #36 under the rear seat as a first attempt get it to recalibrate the electronic actuators. Then turn on the ignition switch, but not the engine, and don't touch any HVAC controls for 90 seconds. Listen to the whirring as they recalibrate themselves. Then try the HVAC.

I could not find a fuse box under the rear seat. Am I blind? Is this the "rear fuse" talked about in the other threads you pointed me to?

Thanks for your help.
 

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...I disconnected the battery while repairing the headlight. Hooked it all up, and now the A/C does not work at all. When the A/C button is pushed, the accumulator gets cold and the clutch on the compressor starts and stops like normal. I'm pretty sure the A/C is working. However, it just blows hot air.
Disconnecting the battery will trigger a recalibration of all HVAC actuators the next time you start the vehicle. If you interrupt the recalibration by touching ANY HVAC controls in the first 90 seconds or so, it ends up in a funny state, and might not work at all. You need to either pull the battery again, or fuse 36 in the rear fuse block. Then put the fuse back in, start the car, and don't touch anything for 2 minutes to be sure. Sometimes, a weak actuator can fail the recalibration, but it's worked fine for YEARS before the battery got disconnected, because it never had to run a recalibration.
Also, I pulled the fuse under the hood for the blower, but if the fan speed control is on 1 through 4, the blower still runs. WTF? If it's on 5 it quits. Does it sound like there is a short somewhere?
No, that's entirely normal. The BLOWER fuse (#35 under the hood), strangely enough, only runs speed 5. The other speeds are run by fuse #44 in the rear.
About a year ago we did have an aftermarket stereo put in, so the whole control panel was taken apart. However, this problem didn't start until a few months ago.
Then it's not related. Didn't think it would be.
I could not find a fuse box under the rear seat.
You wuz robbed! ;)
Am I blind?
It's there. I absolutely GUARANTEE it. Check the Owner's Manual for more hints as to where it is, but the region of the vehicle that can be described as "under the rear seat" is a pretty small volume. Try again.
Is this the "rear fuse" talked about in the other threads you pointed me to?
Yep. And it's an important part of your car to get to know. ;)
 

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Discussion Starter · #6 ·
Wow. Thanks for going easy on me there. I feel like an idiot. I was going off of memory of what it looks like under that seat, and could have sworn I never saw a fuse block....anyway. :duh:

Ok so I pulled the fuse, started the car, waited a few minutes, put the fuse in....nothing. Then I get back to the computer and see you said "You need to either pull the battery again, or fuse 36 in the rear fuse block. Then put the fuse back in, start the car, and don't touch anything for 2 minutes to be sure."

So now I think I didn't do it right. So I pull the fuse, start the car, put the fuse in right away and then don't touch anything for two minutes? Or pull the fuse, put the fuse back, THEN start the car and wait?

Thanks.
 

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My post said exactly: "Then put the fuse back in, start the car, and don't touch anything for 2 minutes to be sure."

:yes:

and then you repeated back: "Then put the fuse back in, start the car, and don't touch anything for 2 minutes to be sure. "

:thumbsup:

I think you should put the fuse back in, start the car, and don't touch anything for 2 minutes to be sure.

:undecided

If this doesn't work, then you need to start thinking about changing out one or more of the actuators behind the dash.

 

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Discussion Starter · #8 ·
Ok no need to be a smart ass. ;) I'm only making sure because I don't see how pulling a fuse when no power is going to it is going to do anything. The car is off and you pull out the fuse then put it back in...how does the actuator know you did anything?

Either way, it didn't work. We get no A/C from either control up front or back seat. I don't think all these actuators would go out at the exact same time. Is there one that controls where the air is coming from....heater core or A/C?
 

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Ok no need to be a smart ass. ;)
But, but, but - it's my NATURE! :raspberry :tiphat
I'm only making sure because I don't see how pulling a fuse when no power is going to it is going to do anything. The car is off and you pull out the fuse then put it back in...how does the actuator know you did anything?
Ahhhh, I forgot most folks don't know this little dirty secret. The trailvoy evil design team wired up CONSTANT 12V, not switched by the ignition switch, to almost all intelligent modules in the vehicle including the HVAC controllers. They go to sleep (when the BCM tells them to) after the ignition switch is turned off, but they need constant battery power to retain their calibration memory. That's why replacing the battery is the event that triggers most of these weak actuators to fail. Pulling the fuse at any time will erase this memory, and force a recalibration next time the ignition turns on.
Either way, it didn't work. We get no A/C from either control up front or back seat. I don't think all these actuators would go out at the exact same time. Is there one that controls where the air is coming from....heater core or A/C?
The TEMP actuators are the ones that control airflow from heater core versus AC. Yes, both shouldn't go out at once. Is your AC compressor clutch spinning and your receiver/dryer cold under the hood when you should be getting AC and you're not?

I posted the picture of where the actuators are. Can you look at the control shaft of the TEMP actuators and see if they move at all when you rotate the control? If you pull the fuse again to trigger the recalibration, can you see them move CW and CCW when you again turn on the ignition?
 

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Discussion Starter · #11 ·
Ok, another instance in which the simplest solution is usually the correct solution...

Pulling the fuse didn't work for me. I tried it multiple times. As I started taking apart the underside of the dash to look for actuators I thought, "I wonder if I just disconnected the battery again." So I did, and of course that reset everything. We now have A/C and will be able to enjoy our upcoming road trip on the 4th.

Lesson learned here: sometimes pulling the fuse works, sometimes disconnecting the battery works. Better to try them both.

Thanks for all your help! :thumbsup:
 

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Amazing. Thanks for the report. Will have to think for a while what the root cause could have ultimately been. Sounds like Win Vista. Reboot twice and take two aspirin and call Bill Gates in the morning.
 

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Ok, another instance in which the simplest solution is usually the correct solution...

Pulling the fuse didn't work for me. I tried it multiple times. As I started taking apart the underside of the dash to look for actuators I thought, "I wonder if I just disconnected the battery again." So I did, and of course that reset everything. We now have A/C and will be able to enjoy our upcoming road trip on the 4th.

Lesson learned here: sometimes pulling the fuse works, sometimes disconnecting the battery works. Better to try them both.

Thanks for all your help! :thumbsup:

We'll see. Sompin' ain't right. the roadie knows all (and has the patience of a saint). Coffee time:coffee
 

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Discussion Starter · #14 ·
Agh you jinxed me filthyfingers!

Back to square one. Well maybe square two. I've at least figured out how to MAKE it not work.

If the dual controls are both in the COLD position, all is fine. A/C works great.
If the driver control OR the passenger control is moved to a warmer setting, it will warm up to the desired temp....all is ok still.
However, if BOTH controls are moved to any position other than cold, after approximately two minutes (either driving or idiling) it will switch to completely heat. :suicide: Turn the car off, it resets, A/C works again.

So are both actuators screwed up then? Why would they work fine independently, but when both changed it fouls up?
 

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Much more likely to be a bad control module than TWO bad actuators. Actuators usually fail the calibration, or work OK for the rest of their natural lives. There's no cross connection between the two actuators except the control module, unless there's an odd fault with the position feedback sensor reference voltage that's shared between the two actuators.

Start looking for a buddy to swap control modules with, or scan Ebay for a cheap replacement.
 

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Discussion Starter · #16 ·
Much more likely to be a bad control module than TWO bad actuators. Actuators usually fail the calibration, or work OK for the rest of their natural lives. There's no cross connection between the two actuators except the control module, unless there's an odd fault with the position feedback sensor reference voltage that's shared between the two actuators.

Start looking for a buddy to swap control modules with, or scan Ebay for a cheap replacement.
Control module as in the blower speed control module that everyone seems to have problems with? The blower works properly at all speeds whether blowing out heat, A/C, or heat when it's supposed to be blowing A/C. But the "cross connection between the two actuators" you talk about through the control module could cause them to quit working?

We spent the 4th out at my wife's grandparents' house. Her grandma also has an '03 TB...same everything down to the color. I wish I would have known to try switching out the resistors then. Too bad she's 3 hours away!

Also roadie, I saw in another post you told someone if they had a meter they could test their blower control module.
1) I assume, since you didn't mention it, that all the displays for the control module are OK.

2) The problem is in the fan, the speed module, or the wiring. To distinguish among them requires a meter and knowledge how to use it, or throwing money at the problem like a new speed module. Do you have a meter? I could give you the schematic if you want to go poking about for voltages.

3) If you have a meter, start by confirming the fat red wire to the speed module has 12V. Then force the fan speed to high, and see if the purple to the blower motor has 12V and the black has zero.

4) If you don't have a meter, buy some good beer and hold a sign out on the street:

Free Beer for Electrical Troubleshooting Help!
Would it do me any good to run through this test quick to see if the module is working properly?
 

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Discussion Starter · #18 ·
No the one with the brains and the controls and the buttons. The blower speed control is just another peripheral like the actuators.
Humor me a second and check out:

http://trailvoy.com/staff/pdf/trailvoy_parts.pdf

I am looking at page 16 of 33, Instrument Panel, part #30: A/C/Heater control. Is this what you're talking about? It's the only thing I can think of with controls and buttons.

If so, is there a way to test this instead of just buying one and crossing my fingers...or stealing it from my wife's grandma?
 

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There is a chance, a very small chance that I might actually be of some help here. My 02 Envoy had the same symptoms several months ago, after having my heater core replaced. After weeks of fooling around with actuators and wasting everbody's time around here, it became clear that the controller was the culprit.

Several more weeks and I finally got one off ebay. While installing it I discovered that the guy who replaced my heater core never reconnected 1 of the 2 connector blocks on the back of the controller:mad: I reconnected it and all the symptoms you described above - disappeared. So now I have a spare controller. Its manual not electronic, p/n 21999161 I think. If you need it p/m me.
 

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If so, is there a way to test this instead of just buying one and crossing my fingers...or stealing it from my wife's grandma?
Sure. Take it to a dealer and their tech tool can talk to the module and if your problem happens while you're there and it's not intermittent, then voila, they can tell you it's bad.

Oh, they probably charge more than buying one on Ebay.

The free diagnostic path is trailvoy.
 
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