I have a 2007 hummer h3 that has been sitting in the garage the last two months while we have been out of state. When I got back the battery was dead. Jumped it and it starts fine but when I click the ac button is flashes a few times and goes off. No ac off error or anything. After a few mins it seems to work and then intermittently goes off again. Same cycle every time I get in the hummer.

i should also add that calibration of the control module doesn’t work now either.

any recommendations?

 

Charge the battery completely. If you haven't already, replace the crappy azzed OEM Battery Terminal Connectors with a quality aftermarket set like Stingers. Next time you leave town, put a Battery Tender on the truck.

Once the battery is fully charged, start the truck and see what happens. It will not calibrate when it is not getting consistent proper voltage.

 

A/C signal comes from blower motor circuit. Try full fan speed(4) then depress a/c button.

 

Ok so this seems to work. What would cause this and any clue on how to fix it?

I will change the battery terminals as they’re still original.

 

A/C signal comes from the blower motor circuit. Check here: 15V421000

 

yeah, that is the recall isn't it? I had the recall work done about six months ago. I had replaced the resistor myself about 3 or 4 years ago after the blower control quit working and then I assume the Chevy dealer replaced it when i took it in for the recall earlier this year. Are you saying maybe it has gone bad again? i'm confused as to what you are suggesting, sorry.

My blower seems to work fine on all four speeds...

 

As I previously stated, A/C signal comes from the blower motor circuit, you have to turn the blower fan dial(middle) from O, before pressing the snowflake dial, if you only get A/C on from fan speed 4(bypasses the blower motor resistor), you can check/clean the connector to the blower motor resistor. If your blower motor works on all speeds, yet a/c won't engage, you have a voltage drop issue. Check your battery's resting/charging voltage, and make sure you have good clean tight terminals to the battery.

 

Ok I got it now. yes, I knew that the AC would not turn on if the blower is not on.

Here is exactly what is happening:

If I start the car the AC seems to come on most times. if not I can put the blower on speed 4 and it will come on. The blower itself works on all speeds, but the AC will only engage if I put the blower on speed 4.

I'm leaning towards some kind of voltage issue because what I'm also noticing is that when the AC won't engage the blend door actuator doesn't function properly (one click from full face sends it full defrost) and the temp actuator also doesn't work properly (one click from full cold sends it all the way hot). Once the AC starts working the actuators also start working properly.

I will check the voltages tomorrow and also change out the battery terminal connectors and then report back.

 

Hi Hummerz and Doc - so I tested the voltage in between rain breaks here in Houston (damn tropical storm). Resting voltage was low - 12.4. Charging voltage started high - around 15.2 but then steadily dropped to around 13.7 after a few mins. I had a work call for 30 minutes so I left it running during that and came out to read it once more and it had dropped to about 12.8 while running.

I will definitely swap out the terminal connectors but does this feel like an alternator issue perhaps? It is the original alternator.

I really appreciate ya'lls help on this. This is a 2007 H3, and we are the original owners. Some time I will post pics of it but the inside looks pretty much as clean as it did the day that we bought it, and the outside is in pretty damn good shape for being out in the Texas heat these last few years since we have three vehicles now. I LOVE this Hummer and drive it most of the time to keep miles off of another car. I desperately want to get this issue fixed!

 

Battery & charging voltage perfect. Time to check the hvac control module, pull/clean connector contacts.