2007 Sierra Classic 3500 Climate Control Issue

[GMC D-Max]

Maybe somebody can shed some light, as I'm scratching my head on this one:

Virtually overnight, my climate control blows almost no heat. It used to be almost too warm set at 68, now I don't get heat until I crank it all the way up (90). It's full-up on coolant (have never emptied the reservoir), and I can hear the heater door moving when I raise and lower the temp. I can't think of what might have caused this, other than it seemed to coincide with my last fuel filter change (did I possibly bump something while changing it?). The only other thing I can think of is, I had an issue with an aftermarket alarm/remote starter I had installed, which uses an interface module to "talk" to the truck. I know it's capable of extensive integration with a number of systems, so is it possible it's messed with the climate control unit? I didn't have any problems after it was installed initially, but I had to take it back for a few tweaks to the programming (disable priority unlock, and an issue where it wouldn't always unlock on the first button press).

(Please, no GM Reps telling me to go to my nearest dealer... that's for people that don't like to work on their vehicles. ;) )

[More Power]

I don't have experience with the climate control, but I do know that the Tech II can connect with the system and can be used to test the various modes. Might be worth a shot if some other idea isn't forthcoming. Jim

[GMC D-Max]

Thanks for the reply, Jim!

I've been thinking about taking the truck in to a dealer to have the AC serviced (it's not quite up-to-par, compared to my old truck after some TSB fixes were applied), and thought about having them look into it. I just wanted to make sure it wasn't something I did, before I took it in.

Think disconnecting the batteries for a while might have any effect?

[GM Customer Service]

Thanks for the reply, Jim!

I've been thinking about taking the truck in to a dealer to have the AC serviced (it's not quite up-to-par, compared to my old truck after some TSB fixes were applied), and thought about having them look into it. I just wanted to make sure it wasn't something I did, before I took it in.

Think disconnecting the batteries for a while might have any effect?


If you do decide to take your vehicle into the dealership could you please keep us updated? If things don't go correctly feel free to contact us so we can get involved.

Thank you,

Jessica L.
GM Customer Care

[GMC D-Max]

Still having this issue (getting serious about it, now that it's getting colder, here), and have come to a few conclusions:

1. It's not the interface module for the alarm interfering. I disconnected it, and same issue... blows cold until I max out the temp setting on the head unit.

2. Cooling system had no air in it. As soon as I cracked the bleeder, coolant appeared. Did it cold and hot. (I really didn't think it was a coolant issue, anyway. If I set the thermostat at 90, I get heat. If I drop it to 89, no heat.)

Perhaps a stuck heater door or bad heater door motor? Unfortunately, I don't have a set of manuals for this truck to troubleshoot it, myself.

Does anyone have manuals that cover the '07 Classic that would be willing to take a look for me?

[More Power]

Can you (or a tech) interact with the HVAC system using a Tech II? Might be a way to test the system. Jim

[Kennedy]

Are you running in auto mode?

It could be related to the ambient air temp sensor. The HVAC reads ambient air temp and Uses that to calculate the delivery temp of air to the cabin. I've never studied the system, but I can tell you if the AAT sensor reads hot, the HVAC system output decreases temp dramatically.

When I carry my plow in winter the air flow through the radiator is disturbed and likely reversed. Both the OAT and AAT start to read 100°f or so and the HVAC starts to get chilly inside. The AAT sensor for the HVAC is up in the grill area rather than in the HVAC air intake as it should be.

[GMC D-Max]

OK... I finally got into the dealership this morning, and they found code B0164 "Passenger Compartment Temperature Sensor Circuit", and my receipt shows "aspirator shorted". So, the cabin ambient temp sensor is shot. Stupid me, I left without checking with the parts department to get a part# and price. Service department wanted $250 to replace it, and I told 'em "thanks, but no thanks". For that simple of a part, I'll do it myself.

I'm just hoping the alarm (Clifford) I had installed, which taps that sensor for triggering the defroster in cold weather on remote start, isn't the cause of the failure. At any rate, the service writer said failure of this part is fairly common.

Thanks for all your input, guys... especially Jim and John!!

More info, in case anyone here has the same problem (come to find out, this is pretty common, now that I'm using different search terms on the innerwebs):

The symptoms:
HVAC will not produce any heat unless set to 90 degrees. Anything less, and it will blow COLD.

Solution:
Aspirator (that little thing in the headliner above your left ear that you mistook for a mic/speaker/whatever) is bad. It has a little fan in it, and sometimes the fan goes bad and makes noise before the sensor actually fails. Mine failed without making a sound. Fairly easy to replace, and only about a $25 part (plus shipping).

Part#: 20931026 (replaces part#s: 15029252 & 15-51256)

Replacement Procedure (lifted from another forum):

1. Remove the left windshield garnish molding. (Pull the molding straight out to release retainers)
2. Remove the left center pillar assist handle & center pillar garnish molding (crew cab). (Hold molding firmly & pull straight out. Handle is held on with (3) screws. Probably only need to pull out the top of this molding)
3. Remove the left sun visor. (3 screws & an electrical connector if lighted mirror)
4. Remove the headliner retaining screws. Just the screws that hold the headliner in that area I believe.
5. Gently pull down the headliner.
6. Remove the inside air temperature sensor from the headliner.
7. Disconnect the electrical connector from the inside air temp sensor.
8. Reverse order of steps to put it all back together.