Ambient Air and AC

[agarb]

2019 GMC Sierra At4 5.3 70k Miles

Check engine light is on, Code is ambient air temp sensor.

AC is hot. 100 degrees out truck says "Ice possible, drive with care"

Take it to dealer, they want $2100 saying that the AC compressor is bad (I didnt go through with it)

 

I change the Ambient air temp sensor, clear the code.

Light goes off, AC blows 60 when the truck is moving. Blows warmer when the truck is sitting still.

Check engine light is back on. Same Code.

Air blows cool when moving at highway speeds warm when sitting still. outside air temp seems to be accurate. 

 

What should I look at from here?

[Steve-2019]

Did you use an genuine GM part for the ambient sensor or aftermarket?

[Transient]

I'm no expert, and I'm not a fan of diagnosing vehicles over the phone (literally, since I'm view the forum that way), but it does seem the dealer may be correct about this one. 

[silveradosid]

is the a/c compressor making any strange noises, are the engine fans working . could be low on freon. 

[KARNUT]

I’m not an expert on this. I would check the fans. Seems 60 while moving should be pretty good. Before electric fans vehicles would warm inside sitting still. 

[jaxcam02]

1 hour ago, KARNUT said:

I’m not an expert on this. I would check the fans. Seems 60 while moving should be pretty good. Before electric fans vehicles would warm inside sitting still. 

I would agree with this, if it cools while vehicle is in motion and not while stationary, that points to the radiator fans for me. Check to see if they come on when engine is hot. If they don't you should see engine temps rise while stationary as well.

[KARNUT]

1 hour ago, jaxcam02 said:

I would agree with this, if it cools while vehicle is in motion and not while stationary, that points to the radiator fans for me. Check to see if they come on when engine is hot. If they don't you should see engine temps rise while stationary as well.

The way I understand it. One should run whenever the AC is on. No matter the temperature. 

[redwngr]

Crap in fins of condenser (and/or) or rad reducing airlfow....

Anything installed in front of it?

[agarb]

On 6/22/2023 at 4:03 PM, Steve-2019 said:

Did you use an genuine GM part for the ambient sensor or aftermarket?

Yes sir, I got a GM one from Advanced. It has all the same markings as the old one.

[agarb]

On 6/23/2023 at 6:50 AM, silveradosid said:

is the a/c compressor making any strange noises, are the engine fans working . could be low on freon. 

No strange noises that I can tell.. I hooked up a digital gauge that came with the Freon can. It showed that it was inside the window of a proper charge.

[silveradosid]

what pressure did it show , what was the temp outside

[repairman54]

Can gauge cannot be trusted at all. It only reads the low side and they are not accurate. Need real high and low pressure gauges on it to get the full picture. 

Dealer had real gauges on it, possibly the high side is low so that would indicate a weak compressor.

[KARNUT]

I’ve used the low can filler if my AC gets a little warm. Just used it on my avalanche with great results. I could and probably have a slow leak. If it last the season I’ll be tickled. Of course I know my truck and the AC still was cycling but quickly. Read the instructions it could bail you out. You have to have reasonable shade tree skills. 

[agarb]

I’ve checked both rad fans. Both working and running.  Check engine light comes on when i crank up most of the time and the AC blows hot. Then cools down when I’m moving. Truck is a 2019, I hopped in my buddys truck last night and my AC, even at its coldest, is no where close to the temps his blows. 

[2016 Sierra Owner]

Look at the engine temp when sitting and when running. My wifes traverse temp sending sensor went out in her car. It said it was overheating on the temp gauge. When that happens the A/C will cut off to reduce the load on the engine that thinks it's overheating.