Heater issue

[Lewiz VenomH3]

I have a 07 Hummer h3 3.7 I5
Having issue with heater not working.
Ive searched online and some folks with similar problems have tried replacing the thermostat,which I did yesterday along with the ac resistor.
The hoses going into the firewall are hot and there's plenty of coolant. Ive also tried the ac reset and no changes.
Any ideas?

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[Jeepwalker]

Can you hear the heater box doors move, if you change the dial from defrost to heat ...and vent settings?
If you move the dial from cold to hot (and back) can you hear a door move?

I haven't had to work on my H3's heater, but nearly all modern cars have a small electric drive motors which moves internal doors that adjust heat and cool/and outlet air location (vent/floor/def). They can and do fail. I've replaced probably 4 of them in a Jeep Grand Cherokee we have.

https://schwarttzy.com/wp-content/uploads/2013/01/Hummer-H3-HVAC-1-4-1.pdf
(Read Pg 2 and beyond for an overview)
https://schwarttzy.com/wp-content/uploads/2013/01/Hummer-H3-HVAC-1-4-1.pdf
(Read the General Description on pg 83, and then the "Too Cold" section starting on pg 61)


Somewhere in those pages it should help you troubleshoot the problem. Hope it helps

 

[Lewiz VenomH3]

Nope. Caant hear anything change when turning knob from cold to hot

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[Jeepwalker]

Read the troubleshooting tree in the link above, it should narrow down where the problem is. I suspect there are some ohm readings you can take with a multimeter and figure out if a motor burned out. As I said before I haven't personally had to dig into my H3's heater box, but I have on other vehicles. Usually there's a blend door between the heater core and the AC evaporator coil that moves to deflect all air through the heater core (in heat mode). That door probably isn't actuating, weather it's a crapped-out motor or [gulp] a broken door hinge. But I haven't read the door hinges are weak in these H3's so that's probably not it. Hopefully if the motor needs replacing (~$25) it's easy to access. Should be in the shop manual pages linked above.