Cooling fans coming on max after cold engine start, stays on till engine shutdown

[swathdiver]

08 Tahoe.

Weird it started the other day while driving on the first really hot day out. I noticed the snowflake icon on my a/c flashing and my ac got warm. I got out the truck at my next destination with it running and the fans were on wide open. I checked coolant, good. A/C belt, good. Got out my scan tool. No codes. Coolant temp showing 190. So I shut it down. Next morning did a cold start. Same thing fans wide open when cold and A/c wont work. I replaced the coolant temp sensor like some suggest but its still present. I thought maybe a bad relay but they stick on even when truck is off. I see thread but none solved. My thoughts are in the direction of a high pressure switch or maybe and issue causing a high pressure backup in the system.

Any direction is appreciated.

You are probably low on refrigerant. My two cents is not to throw parts at it as such can open other cans of worms.

Put a manifold on the high and low side of your AC system and compare the pressure with the outside temp to see if she's or low or not. If so, my advise it to empty the system, make sure it holds a vacuum for 30 minutes or so and then introduce the proper amount of refrigerant by weight, using a scale if necessary. Tahoes with rear AC hold 2.6 pounds of R134 if memory serves.

 

[Geotrash]

You are probably low on refrigerant. My two cents is not to throw parts at it as such can open other cans of worms.

Put a manifold on the high and low side of your AC system and compare the pressure with the outside temp to see if she's or low or not. If so, my advise it to empty the system, make sure it holds a vacuum for 30 minutes or so and then introduce the proper amount of refrigerant by weight, using a scale if necessary. Tahoes with rear AC hold 2.6 pounds of R134 if memory serves.

In addition, I'm pretty sure that you can see the A/C system pressure during operation with a Tech2 or equivelent. Yes?

 

[j91z28d1]

In addition, I'm pretty sure that you can see the A/C system pressure during operation with a Tech2 or equivelent. Yes?

At least on mine, use tech 2 or others can see both low and high side pressure.


I still fill like something is defaulting the fans on. like I've forgotten to plug the temp sensor in and it turns the fan on max any time it's running. he's replaced it thou, maybe a tranny temp sensor?

 

[Geotrash]

At least on mine, use tech 2 or others can see both low and high side pressure.


I still fill like something is defaulting the fans on. like I've forgotten to plug the temp sensor in and it turns the fan on max any time it's running. he's replaced it thou, maybe a tranny temp sensor?

Good thought. The fans were running like that on my 2012 so I replaced the coolant sensor with a genuine GM from Rock Auto, even though the gauge was reading correctly. Problem solved. He may have gotten a counterfeit sensor, or they sometimes ship with the pigtail and connector because they're often damaged from heat and exposure. Might have a bad wire on his pigtail.

 

[Foggy]

To the OP: I may have missed it, but your temp gauge in the SUV is about
as worthless as a dummy gauge.
Replace the ECT sensor on the drivers side cylinder head with a "good" one ...
Make sure your coolant is good and you don't have any air pockets.. that
will trigger the fans to be on as well.

 

[ilikemikes]

To the OP: I may have missed it, but your temp gauge in the SUV is about
as worthless as a dummy gauge.
Replace the ECT sensor on the drivers side cylinder head with a "good" one ...
Make sure your coolant is good and you don't have any air pockets.. that
will trigger the fans to be on as well.

I have the same issue, fans come on with cold engine. Replaced leaking radiator and thermostat last year. I'm going to try a new ECT and see if this solves the issue.