Heater being weird - thoughts?

[aces-n-eights]

So the outdoor temps are going down and i've started using the heater. The heater blows ice cold air for probably 10 minutes or more after the engine has come up to operating temp. It then will blow heated air as it should. The Tahoe is an LT and i have the climate controls set at 75 degrees and pushed the "Auto" button.

I'm thinking a stuck or sticky thermostat.

I've looked at a couple of youtube vids and replacing the t-stat doesn't look too hard. One vid suggested replacing both the t-stat and the housing. Any need to do that, or can i just replace the t-stat?

Anything else that might be causing the problem?

 

[ScottyBoy]

You sure its a whole 10 minutes? Mine takes a while, but not 10 minutes unless its REALLY cold outside. I have also noticed that it takes a lot longer for the air to get warm if I have the fan on high. I run the fan at low or just a hair above low until it starts to feel warm, and then I will turn it up higher. I noticed that it gets warmer faster when I do that. I guess with the fan blowing cold air across the heater core, that's just making it take longer to heat up, so I stopped blowing it on high.

 

[BeenChevy]

What's the temp outside in AK when you notice this issue? Are you driving the vehicle or letting it sit idle during the 10 minutes?

 

[aces-n-eights]

With the climate control system in "Auto" the fan runs up pretty high, like the heater core is warm and it's trying to warm up the truck. The air is very cold, almost like the AC is on. Then at some point it starts blowing warm air.

It really seems like the t-stat is stuck and then releases and works properly.

The outside air is in the low 30s and i'm driving the car...it's not idleing...

It seems like this is a change and not how it has been working...

Thanks for the replies!

 

[ScottyBoy]

I seriously doubt that the thermostat is sticking like that every time. It would make far more sense that the blend door (the door in the AC ducts that changes the air from hot to cold) is getting stuck. But I could gave sworn that I read several times that the default position is on hot. So when its unplugged it the truck is off, it switches to the hot side.
Try setting the AC controls to manual, and turn the fan speed down and see if that makes any difference.
Another possibility is that the ambient temperature sensor is acting up, since you said this issue occurs with the Controls set to Auto. Like I said, try it in Manual and see what happens. If it warms up faster with the fan on low, then try it another time with the fan on high but still on Manual setting. If it seems to work fine on Manual no matter the fan speed, that tells me that you should start with the temp sensor. That ambient temperature sensor us what senses the interior temperature of the truck and it adjusts the temperature output from the AC/Heater, no matter what you actually set the temperature setting to. If you set it to 75 and the truck thinks that the interior is already at 75 (due to a faulty temp sensor) then it will not blow hot air.
So test it out on Manual and let us know what happens.

 

[Rocket Man]

You can also try the HVAC reset procedure. I created a post in the tech section for the how-to.

 

[retiredsparky]

In certain modes (defrost) the AC compressor will run even when asking for heat. This will obviously cause the air to be even colder. I don't recall if the snowflake symbol shows up on the display when in that mode.

It is possible that your engine coolant thermostat is sticking open as you seem to be saying. Not a common issue, but the symptoms indicate that is a possibility. Does your coolant temp gauge seem to take longer than normal to rise? Even in cold weather, the gauge should be moving up within less than 5 minutes of driving.

 

[BeenChevy]

I'm in the 30's here all week. I'll select auto in each truck as I take them anywhere and watch the clock and engine temp.

I recall even at -20F it they were at 200 before 10 minutes and heat was hot.


Update:

05 Tahoe 34F engine 209F @ 9min. Heat set to Auto 90F front and rear felt warm after 3-4 minutes.

 

[Rocket Man]

In certain modes (defrost) the AC compressor will run even when asking for heat. This will obviously cause the air to be even colder. I don't recall if the snowflake symbol shows up on the display when in that mode.

From what I understand the compressor runs for a big to remove moisture from the air during defrost, it's not in a cooling mode.

 

[aces-n-eights]

Thanks for the replies, guys. Scotty, I will try it in manual mode and see if that makes a difference. I will also look at the HVAC reset - thanks RR. The engine temp seems to come up to normal operating temp in a normal time.

I'll pay a bit more attention to the times it takes for various events to happen... normal temp, cold vs hot air, different settings.

Thanks again.