Heat only works @90*

Spaceman Spiff · Sep 9, 2018

05 Tahoe, auto climate control.
Just purchased in late July.
Today temps went down to mid 50’s, so I figured it would be a good time to test the heat out.
Well, it only blows hot/warm at the max, 90* setting. Even if I put it to 89*, it starts to blow cool air.
Set both sides to the same temp, or on different settings, it’s the same thing.
Is this common? I would say heater core flush, but why would it only work on max temp?
A/c blows cold, no problems there.

Doubeleive · Sep 9, 2018

either you need the blend door actuators recalibrated, or the actuators are bad, or the control module is bad, pretty unlikely to be anything with the heater core at all unless your truck has no thermostat and runs cold all the time

swathdiver · Sep 9, 2018

What He said! ^^^^

V30Crewcab · Sep 25, 2018

actually my dads 2000 truck didn't' have heat last year, ended up flushing the heater core with a garden hose and suddenly it had heat again. but it didn't' have any no matter how hot you set it, so probably not your issue.

MrBalll · Oct 1, 2018

Found out a few days I have this issue also. Is there an easy way to tell which needs to be fixed as far as an actuator or the control module?

Doubeleive · Oct 1, 2018

MrBalll said:
Found out a few days I have this issue also. Is there an easy way to tell which needs to be fixed as far as an actuator or the control module?

you can pull the cover off under the glove box and visually watch the actuators to see if they rotate when making adjustments on the controller, they have a round slotted/hole, watch the hole to see if the mechanism moves or not.
some have a plastic slot and some are metal not sure which anymore on the nbs but they all operate the same, but this what you want to watch move
**also different actuators do different things some direct air up/down, some divide the hot/cold, so if you don't see one move then just move the controller to up/down etc. if it doesn't move for any setting then it may be bad.

Jack Treehorn · Feb 22, 2024

I'm not sure if this applies to all GMT800 GM trucks and SUV's, mine is a 2003 Yukon Denali. If your heat only blows hot when your dual climate control is set to 90 degrees, I can tell you what is probably not the issue. It's probably NOT blend door actuators, your climate control module, blower motor resistor or recalibration of your blend door actuators by removing fuses. And if it's blowing hot when set to 90 degrees, your heater core is likely fine. My issue (and dozens others with the same symptom on different forums) was the cabin air temp aspirator (air temp sensor) right above the driver's left ear in the headliner. You can still get these genuine AC Delco parts (P/N 22834330), they're about $40 and they are upgraded with better support for the thermistor. The fan inside mine was fine, the thermistor failed. The fan can also fail too or make a buzzing noise. There are lots of replacement videos online, should take about 15 minutes of carefully peeling down the headliner to access. Good luck.

strutaeng · Feb 23, 2024

Jack Treehorn said:
I'm not sure if this applies to all GMT800 GM trucks and SUV's, mine is a 2003 Yukon Denali. If your heat only blows hot when your dual climate control is set to 90 degrees, I can tell you what is probably not the issue. It's probably NOT blend door actuators, your climate control module, blower motor resistor or recalibration of your blend door actuators by removing fuses. And if it's blowing hot when set to 90 degrees, your heater core is likely fine. My issue (and dozens others with the same symptom on different forums) was the cabin air temp aspirator (air temp sensor) right above the driver's left ear in the headliner. You can still get these genuine AC Delco parts (P/N 22834330), they're about $40 and they are upgraded with better support for the thermistor. The fan inside mine was fine, the thermistor failed. The fan can also fail too or make a buzzing noise. There are lots of replacement videos online, should take about 15 minutes of carefully peeling down the headliner to access. Good luck.

View attachment 422002

Thanks posting this! I've been having this problem since I bought my 06 Suburban a few years ago. I thought it was my controller.

Last night I popped the little grill cover and sprayed some Deoxit in there and this morning my temperature worked!!!

I also sprayed the knob (removed the dial) but it's kinda tight in there and I don't really know if anything got inside.

If the problem permits I will replace the sensor.

viven44 · Dec 8, 2024

strutaeng said:
Thanks posting this! I've been having this problem since I bought my 06 Suburban a few years ago. I thought it was my controller.

Last night I popped the little grill cover and sprayed some Deoxit in there and this morning my temperature worked!!!

I also sprayed the knob (removed the dial) but it's kinda tight in there and I don't really know if anything got inside.

If the problem permits I will replace the sensor.

@strutaeng

I tried CRC "Electronics cleaner" on mine, no luck. Only blows Hot when set to Max heat, anything slightly below that is cold.

I guess I'm looking at a new sensor?

strutaeng · Dec 8, 2024

viven44 said:
@strutaeng

I tried CRC "Electronics cleaner" on mine, no luck. Only blows Hot when set to Max heat, anything slightly below that is cold.

I guess I'm looking at a new sensor?

Yes, that's what my problem was in the end. I can't remember what it's called or the part number, but there's a thread somewhere here (edit: this thread shows the part on #7...I didn't read the previous posts. I posted what the sensor looks like and how to replace it on a different thread. It's like $40 IIRC.)

Heat only works @90*

Spaceman Spiff

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