05 2500 hvac started acting funny

[05duramaxbro]

i noticed a funny mildew like smell in my truck when i turned on the defrost. usually my truck blows pretty warm when i set it at 78 and is very comfortable for me at 73 with the defrost and floor setting on. lately 73 feels like its blowing super cold and 85 feels kinda warm. its like the AC is on whenever the defrost is on. it never seemed to do this. didnt recently disconnect the batteries or anything. just started happening. when i have it in vent setting and vent/floor setting, it goes back to the way it used to feel.

any help would be greatly appreciated.

 

[clrussell]

Ac does run with the defrost to dry out the air

 

[OregonDMAX]

You may have a blend door going out

 

[Chevy1925]

I'd do the hvac relearn before I touch anything.

 

[OregonDMAX]

I'd do the hvac relearn before I touch anything.

Care to explain, I asked a similar question a few years back and that wasn't mentioned

 

[clrussell]

I'd do the hvac relearn before I touch anything.

This..

I've not figured out how to do it without a scan tool though

 

[Hambone]

Not sure if it's the same for the manual climate control
The auto goes as follows
Disconnect batteries wait a couple of minutes
Reconnect batteries
Get in seat and close door
Turn ignition to run position
Set passenger side full hot and drive full cold
Hit auto button
Turn key off and open truck door
Close door
Turn key to run and now driver side full hot and passenger full cold
Hit auto
Turn key off and open door
That has worked for me on several different model year chevys with the auto system
There is also the method of pulling the 40 amp HVAC fuse and waiting a couple of minutes then putting it back in and just turn the truck on and don't touch anything for a few minutes

Hope this helps
But just know this is only a bandaid
Eventually the blend doors do need replacing

 

[Chevy1925]

Care to explain, I asked a similar question a few years back and that wasn't mentioned

the "alternate" method is what ive used but it wont work on our trucks. only for auto climate control and 03-up from what ive seen.

https://www.performancetrucks.net/f.../ac-system-actuator-re-sync-procedure-449773/

This..

I've not figured out how to do it without a scan tool though

see above buddy

Not sure if it's the same for the manual climate control
The auto goes as follows
Disconnect batteries wait a couple of minutes
Reconnect batteries
Get in seat and close door
Turn ignition to run position
Set passenger side full hot and drive full cold
Hit auto button
Turn key off and open truck door
Close door
Turn key to run and now driver side full hot and passenger full cold
Hit auto
Turn key off and open door
That has worked for me on several different model year chevys with the auto system
There is also the method of pulling the 40 amp HVAC fuse and waiting a couple of minutes then putting it back in and just turn the truck on and don't touch anything for a few minutes

Hope this helps
But just know this is only a bandaid
Eventually the blend doors do need replacing

good one to know. i used the remove the 40 amp fuse method. now granted most of the ones ive done this on are ones that had batteries replaced, the other couple have been good thus far.



Id be curious if the tech2 can recal a manual controlled unit. my zone actuator and recir/outside air dont move and the recirc/outside air has a mind of its own. they have been replaced as well as tried a known good hvac head unit with no change....

 

[clrussell]

the "alternate" method is what ive used but it wont work on our trucks. only for auto climate control and 03-up from what ive seen.

https://www.performancetrucks.net/f.../ac-system-actuator-re-sync-procedure-449773/



see above buddy



good one to know. i used the remove the 40 amp fuse method. now granted most of the ones ive done this on are ones that had batteries replaced, the other couple have been good thus far.



Id be curious if the tech2 can recal a manual controlled unit. my zone actuator and recir/outside air dont move and the recirc/outside air has a mind of its own. they have been replaced as well as tried a known good hvac head unit with no change....

Well I have a scan tool handy but good to know!

 

[Hambone]

Lol on my personal truck after about 5 minutes the door switches the heat on driver side so I put in neutral shut off open door start back up and presto!
Been to busy to properly fix but isn't the how it goes haha:rofl:
Not looking forward to removing the dash

 

[05duramaxbro]

thanks for all the replys. i will try the HVAC relearn in a few minutes and see if it helps.

ive also been trying to find all the weird issues with it. it seems like my defrost setting and my defrost plus floor setting is either all the way hot or all the way cold. no in between. this is where its weird, because if i switch to vent mode, it will blow the correct temp. that right there is the reason i think the blend door is still doing its job. correct me if im wrong.

 

[05duramaxbro]

alright so i watched some youtube videos and did some more research and this is what worked for this particular problem i was having. i figured i would share in case anyone elses truck was acting funny.

https://sparkys-answers.com/2011/08/hvac-actuator-recalibration-procedure.html