07 Hummer H3 No Heat
 

Hello fellow H3 enthusiasts.
I'm new to the forum as I recently purchased an H3 with 150k on the speedo.
Its in excellent condition with no rust and runs great. (though it does need a crossmember bearing).

Anyway... Today the heat stopped working. It only blows cold.
The blower fan works fine. The dial that directs the air to vents or floor works fine (top actuator in pic). The actuator for hot or cold seems to work fine (lower left actuator in pic) it turns when you move the dial.

The lower right actuator in pic seems to never move no matter what dial I move.
Does anyone know what lower right actuator is for? Could this be the problem?

Any help or suggestions is greatly appreciated. (and yes, the coolest is full and hoses going into the firewall are hot)

Many thanks in advance.

First thing to check is your coolant level.

Coolant level is fine. Expansion tank is half full and if you take the rad cap off when cool it's to the top.

The other one could be for recirculation/fresh air door. The I5's are bad for thermostats. The temp gauge should be at half after driving for a while. I also did a heater core flush when changing the stat. The heater hoses should be at similar temps when the engine is at normal operating temps. If one hose is cold by feel then your heater core is plugged and may need to be flushed or replaced.

i HAVE THE SAME PROBLEM
 

Hi:
I have the exact same problem. My H3 blower works fine, but just blows cold air. Not that a huge problem in southern California. However, recently I had to drive home in the rain, and it was much colder that usual outside. The windshield fogged up so that I couldn't see. Blowing cold air didn't help at all. So, I am kind of desperate for a fix. Just wondering how you fixed this issue in your H3.
p.s I don't know if this is relevant, but I was having issues with battery drain and finally disconnected battery and took out the on star system. Starts every time now. I only mention this because i heard disconnecting the battery can trigger temp control issue with hvac.
Any feed back would be greatly appreciated.

+1 on probable thermostat problem. If engine runs cool...

No heat to the core.

As stated above most likely a thermostat. Temperature gauge should be reading at half or more. Try an HVAC recalibration. Flush heater core. Could also be a stuck blend door.

If your issue is the thermostat then your engine won’t get hot all the way and will be sitting around a 1/4. The proper temperature reading is over half just a little bit. I had this issue and you will probably have to replace the thermostat. It’s not that hard of a job. You have to remove the driver side wheel to gain access to it. Thermostat $45. Just be careful it to drop the bolts. When you put them back in put some type of tape or paper just so it sticks in the socket. I lost a screw and couldn’t find it for half and hour. Good luck

Awesome. Thank you so much everyone for the help. I like having a plan.
Much appreciated.

Replace the lower right actuator; it takes both to get hot air (been there, done that).