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2004 chevy trailblazer_lt_ext
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Discussion Starter · #1 ·
Hi all,

Sorry in advance if this has been answered already, but I tried searching the forums and couldn't find anything.

1) when I run AC on a hot day, the temperature reading in the front keeps going higher and higher as if it is boiling outside. I shut off the AC and it goes back to normal. I suspect that the sensor is somewhere near the AC motor and is causing the sensor to give the wrong reading.

2) Lately I have noticed that the rear vents start blowing air irregularly even if I have the vents at "0" from the front (i.e. shut off). Even if I set the knob to "R" and allow the rear console to control and turn it off, it still blows air every once in a while! Any idea why?

Thanks
fresh
 

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2003 gmc envoy_slt
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7,190 Posts
I believe the temp sensor is that cluster of little holes in the pillar next to the drivers left ear. Do you have manual or auto-climate control? On my Envoy w/auto-climate control the read-out shows outside temp unless a temp change is checked or changed. There is no reading for inside temp. :m2:
 

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2004 gmc
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The outside air sensor is just under the hood above the radiator on a crossmember, but it's designed that any small amount of forward motion will get fresh air to it. It has been known to fail but it's a cheap and easy part to change. Search for "outside air temp sensor".

What kinds of temps are you seeing, and are you moving or not at the time?

The outside air temp sensor doesn't have a lot to do with AC system performance, unless it fails in a way that reads low like 20 degrees F, in which case the AC compressor will be suppressed and you'll know it. The digital system is constantly reading the duct work and cabin temp to adjust the airflow.

I don't remember seeing an issue with the rear blower like that. Is it disturbing because it's on high speed or something? Could be a flaky blower speed control module. Has it ever stayed running after the key is off? How often, like once an hour or once a minute?
 

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2004 chevy trailblazer_lt_ext
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Discussion Starter · #6 ·
The outside air sensor is just under the hood above the radiator on a crossmember, but it's designed that any small amount of forward motion will get fresh air to it. It has been known to fail but it's a cheap and easy part to change. Search for "outside air temp sensor".

What kinds of temps are you seeing, and are you moving or not at the time?

The outside air temp sensor doesn't have a lot to do with AC system performance, unless it fails in a way that reads low like 20 degrees F, in which case the AC compressor will be suppressed and you'll know it. The digital system is constantly reading the duct work and cabin temp to adjust the airflow.

I don't remember seeing an issue with the rear blower like that. Is it disturbing because it's on high speed or something? Could be a flaky blower speed control module. Has it ever stayed running after the key is off? How often, like once an hour or once a minute?
The sensor seems to function properly and reads the actual (or close to it) temperature outside, until I turn on the AC, at that point, the temp reading starts going up constantly, and more so if the car is idling. I get the feeling that the compressor is somewhere near the sensor and hence causing the heat to go up near the sensor.

As for the rear blower, it is a bit disturbing sometimes as it comes on at high speed. It is not constant and happens whenever it wants to happen. When it does happen, I simply have to play with the control knob in the front to shut it off. I.E. move it from 0, to say 3, then back to 0. Sometimes taking it to R as well. Only to have it happen a few minutes later. It sometimes happens at high speed, and sometimes at low speeds.
 

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The sensor seems to function properly and reads the actual (or close to it) temperature outside, until I turn on the AC, at that point, the temp reading starts going up constantly, and more so if the car is idling. I get the feeling that the compressor is somewhere near the sensor and hence causing the heat to go up near the sensor.
Well, the compressor isn't the major source of heat in the AC system, the condenser is (the thing that looks like a radiator) and the sensor is indeed right above it. To give an accurate reading, you have to have outside airflow over the sensor that isn't coming off of the condenser.
As for the rear blower, it is a bit disturbing sometimes as it comes on at high speed. It is not constant and happens whenever it wants to happen. When it does happen, I simply have to play with the control knob in the front to shut it off. I.E. move it from 0, to say 3, then back to 0. Sometimes taking it to R as well. Only to have it happen a few minutes later. It sometimes happens at high speed, and sometimes at low speeds.
Don't think it's easy to diagnose this unless it fails altogether, or you want to throw money at the problem to shotgun it. The speed control module is difficult to get to, but it gets its commands from the rear control module in the console. And the front switch is naturally involved. You might keep an eye out on Ebay for cheap replacements or cultivate a local buddy with a like vehicle and start trading parts until his starts to go bad and yours is OK. Then quick like a bunny move out of town with no forwarding address, and voila! Your vehicle is now fixed!! :thumbsup:
 

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Discussion Starter · #8 ·
Well, the compressor isn't the major source of heat in the AC system, the condenser is (the thing that looks like a radiator) and the sensor is indeed right above it. To give an accurate reading, you have to have outside airflow over the sensor that isn't coming off of the condenser. Don't think it's easy to diagnose this unless it fails altogether, or you want to throw money at the problem to shotgun it. The speed control module is difficult to get to, but it gets its commands from the rear control module in the console. And the front switch is naturally involved. You might keep an eye out on Ebay for cheap replacements or cultivate a local buddy with a like vehicle and start trading parts until his starts to go bad and yours is OK. Then quick like a bunny move out of town with no forwarding address, and voila! Your vehicle is now fixed!! :thumbsup:
Must start searching for that "buddy" :rotfl:
 
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