HVAC system stuck on heater

[fl0w3n]

I've got two problems going on, I think I know the solution but want to confirm.

First is, truck randomly goes to full heater mode regardless of input from dash controls. It does it on it's own too, not like I go to heat and then it won't come back. Just now sitting idling it all the sudden just started blowing hot after 45m of running on cool. I believe this is the blender door(s)? Something about them getting stuck or the computer not knowing their position so defaulting to a preset location?

Question is, how do I fix it? Is this going to require full disassembly of the dash all the way to the firewall?

Second issue, #5 fan setting only intermittently works - more often it does not work. This is fixed by changing out the blower resistor, correct?

This is on my 04 with the basic dual climate system

 

[2004LB7]

Pull the hvac fuse to try and reset the blend door position. I believe the resistor is correct for the fan speeds

 

[fl0w3n]

Pull the hvac fuse to try and reset the blend door position. I believe the resistor is correct for the fan speeds

Just did a commanded relearn with my Tech 2 on the blend door position, seemed to have worked for now.

 

[fl0w3n]

That worked for about 30 minutes. On my way home it decided to melt me. Great timing because it was 100 out today.

Which part do I need? It looks like I’ll have to completely tear the dash apart to get to it. While I’m there I definitely want to only do it once and do anything else that might go wrong at the same time.

 

[2004LB7]

I remember a post from theferminator mentioning the grease in the blend door gear box dries out and they start to act like that. Supposedly you pop the cover off and clean out the old grease and repack it and be good for another 10 years

 

[fl0w3n]

I remember a post from theferminator mentioning the grease in the blend door gear box dries out and they start to act like that. Supposedly you pop the cover off and clean out the old grease and repack it and be good for another 10 years

@THEFERMANATOR care to shed any light??

Okay but which one? It looks like there's a passenger, driver, mode control, and I'm seeing on All Data DIY a Temp Door Actuator?

 

[2004LB7]

I think mode control is the one

 

[1FastBrick]

#1 the blend door. It's a pain but can be done with small hands and a slim double sided ratchet tool from harbor freight

 

[fl0w3n]

#1 the blend door. It's a pain but can be done with small hands and a slim double sided ratchet tool from harbor freight

But that’s the passenger blend door? I’m getting heat out the driver side?

 

[1FastBrick]

1/4 in, 3/8 in. Drive Long-Reach Dual Flex Head Ratchet

Amazing deals on this 1/4In, 3/8In Long Rch Dual Flex Head Ratchet at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

This bad boy will be your best friend!!! It's a tedious task for sure. I have only had to do one so far about 4 years ago. I think the airbag comes out to do it.

There is not alot of room even if you remove the upper dash pad. Its right next to a vent and there is a small brace in the way.

 

[1FastBrick]

But that’s the passenger blend door? I’m getting heat out the driver side?

I am not sure they are labeled correctly in the drawing. That's the one I had to change out. It blends the hot from cold.

 

[fl0w3n]

Got it, okay. Sounds fun.

Maybe I'll enlist my lady and her tiny hands.

 

[1FastBrick]

I recall it saying something about the bottom one being a blend door too. That one is easy to get to just remove the cover. How ever my case was similar it was hot and even though you turned the AC on it was blowing heat I believe from both sides. And of course it was a hot day like your case...

I also recall there being different parts for digital Vs manual controls. The first motor i ordered was wrong and I had to get a replacement from a local autoparts store.

Fun times. The upper cap of the dash off will give you more room. The stamped metal bracket is sharp so very careful.

 

[1FastBrick]

Oh and the resistor also has to be correct for your style of ac system. This part is usually the cause of the loss of 1 of the speeds for the motor.

Mine shorted on a hot day in Stop and go traffic with the AC on full blast... I almost crashed when it filled the cabin with smoke blowing out the AC vents... I smelled it just before it came out the vents. Melted the pig tail to the resistor. Had to replace both.

 

[2004LB7]

Found this on another site:

Blend Door Actuator:
The blend door actuator is controlled by the vehicle's climate controls. The blend door can open and close at various positions to block or allow air passing through the heater core in order to achieve the desired temperature inside of the vehicle. The blend door actuator is typically located closer to the heater core and evaporator than the mode door.

Mode Door Actuator:
The mode door actuator controls which vent(s) air blows through. The door on this actuator has two positions: closed and open. Today, most actuators are controlled electronically. As actuators wear over time, the plastic gears inside may be stripped or broken, causing them to fail

It almost seems that you may have both going out, but more then likely the blend door would be the issue for your heat problem.

 

[fl0w3n]

Just an update, the driver side is the one on the bottom (which wasn't shown on the diagram). Luckily it's relatively easy to reach.

I took it out and took it apart, and sure enough there was grease over the contact for the doors "position sensing"

Pulled the whole thing apart, used some MAF cleaner and a Q-Tip on the pad, put it back together and did a reset with my tech 2. It's working for now, I'll monitor over the next few days. I'm hoping it's fixed.

I'm hoping the top hard to reach one (passenger side) isn't suffering from the same thing, but it's likely installed with the motor on top so any melting grease would drip away from the contact pad instead of onto it.

 

[1FastBrick]

Nice find!!!

 

[dndj]

Diagram in post #6 is correct, at least it matches the official GM FSM. Blend doors control cold/hot temp, there is one for the driver and one for the passenger side on trucks with independent L/R air temp controls whether manual or automatic option.

Driver blend door is not visible in the diagram as stated, but it's down on the bottom of the HVAC unit, access from the passenger side footwell.

Passenger blend door is the one up on top which is very difficult to get to - special tools as mentioned above. I've also seen Youtube videos where a guy sectioned the plastic air duct to get to it, then taped it back up with HVAC ducting tape when he was done to save time. Not a fan of this approach.

There are 2 other actuators - mode door, which selects which vents the air comes out of. You can see this one if you lay down in the driver footwell and look up above the throttle pedal. Lastly, the recirc door actuator which is up high on the right side as shown in the diagram.


Glad you got it fixed, and thanks for the high-res pictures of the internals. Very helpful!!!

 

[fl0w3n]

Since my fix it has been problem free... up until yesterday. I ran out of fuel in the 100* heat and after putting in 5 gallons I had to prime 3 times (stalled out 3 times) until all the air was out. When I got it running the last and final time, it was stuck on heat. Last thing i needed after pumping for the past 15 minutes in that heat was to get into the truck with the heater on full blast.

After one restart it went away, so I'm hoping it was just a glitch. I'll probably pull the bottom blend door actuator again to just see if any more grease has melted or the gear has broken. It's the bottom one so easy to get to.

One thing it has started doing is hunting for the commanded position, which can get annoying.
I found there's a bulletin on it, but I'm wondering if anyone has used the Tech 2 to push software updates like this? Isn't the subscription pretty pricey?

Correction


Technicians are to perform the normal diagnostic procedures in SI for these concerns. If diagnostics show that the HVAC system door(s) travel below 5 counts (out of the lower range) or above 250 counts (out of the upper range), then update the software calibrations in the HVAC control module. The new calibrations were made available to dealerships as part of TIS2000 incremental satellite update version 2.5, which was broadcast to dealers in February 2006.


The new calibrations have been updated to compensate for the actuator overtravel condition, the actuator hunting and the ticking/clicking noises. The new calibrations effectively eliminate the codes listed above, the default position of the doors associated with the DTCs and opens up the feedback position value. The new calibrations should not be used unless the vehicle has one or more of the customer concerns listed above or a DTC listed above has been set. The new calibrations will not correct any other DTC or NC system performance concern.

 

[Chevy1925]

you should be able to use ACDelcotds.com. then use that to flash from there.