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2017 Terrain 4cyl .. Driving down the road with everything set A/C wise and it will start blowing hot air for a second them go back to ice cold in a matter of 2-3 seconds. Does it at random... Will work again for 30 min - 2 hours and then do it again..

any thoughts?
 

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One possibility would be either your mode or blend door located underdash in your HVAC system.
Do a google search for more info on these doors.
The Body Control Module opens and closes these doors to adjust temp and airflow.
Can you hear clicking when the air temp changes?

The compressor cycles on and off several times a minute, this is normal.
However in the off mode, the air temp can't change that much in 2 or 3 seconds.
 

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I am having similar issues with the A/C on my 2015 (V6 with manual A/C). Will put out 40 degree air at the vents for a while when first starting out, then the air at the vents will climb to 60-70 degrees. Frequently after driving for 30 minutes or so. It will stay at 60-70 degrees for upwards of 20 minutes, then go back to 40 degrees gradually. The air temperature also goes up to 50-60 when sitting at stop lights, and never goes below 50 when just idling.

The system drains just fine, so I know the drain isn't blocked. No clicking from door actuators. The pressure on the low side port this afternoon was 40psi when the ambient temperature was 92F. That seems slightly low to me. I think it should be between 45-50psi. I am thinking about putting some refrigerant in the system to bring the low side pressure up a little to see if that makes a difference.
 

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I am having similar issues with the A/C on my 2015 (V6 with manual A/C). Will put out 40 degree air at the vents for a while when first starting out, then the air at the vents will climb to 60-70 degrees. Frequently after driving for 30 minutes or so. It will stay at 60-70 degrees for upwards of 20 minutes, then go back to 40 degrees gradually. The air temperature also goes up to 50-60 when sitting at stop lights, and never goes below 50 when just idling.

The system drains just fine, so I know the drain isn't blocked. No clicking from door actuators. The pressure on the low side port this afternoon was 40psi when the ambient temperature was 92F. That seems slightly low to me. I think it should be between 45-50psi. I am thinking about putting some refrigerant in the system to bring the low side pressure up a little to see if that makes a difference.
At 86F to 95F the low side on a Equinox should read 30 to 41 PSI.
This spec is for 50% relative humidity.

My first thought when reading your post was a cooling fan malfunction.
 

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Thanks. Guess I will leave it alone then. Both fans immediately come on when the A/C engages, although I guess that doesn't guarantee they are working correctly. The engine isn't overheating, and the engine temperature gauge always reads the same.

I guess I could put new relays in to the cooling fan relay locations in the engine compartment fuse block and see if that makes a difference. Maybe one of the three are bad. Relays are cheap and easy.
 

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2x on cheap relays first. I chased a erratic issue on my old Malibu to the refrigerant pressure sensor. Only acted up on 90+ days making for a fun hot testing process. Cheap part and no Freon loss on replacement as it has a Schrader under it.
 

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The refrigerant pressure switch on the 3.6L Equinox is a hassle to swap out. It is at the front of the engine, at the bottom, sandwiched between the alternator and the compressor. A simple $30 part that would require a lift to swap out. I will have to see if I pulled the passenger wheel well liner back if I could get in there long enough from the side to remove and replace, but GM certainly likes to make things a challenge!
 

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2017 Terrain 4cyl .. Driving down the road with everything set A/C wise and it will start blowing hot air for a second them go back to ice cold in a matter of 2-3 seconds. Does it at random... Will work again for 30 min - 2 hours and then do it again..

any thoughts?
I had a 2014 Equinox intermittent same issue. Would occur 2-5 times per year. Never figured it out. Believe it was a thermostatic switch in the system that would overheat and shut the compressor down to protect the compressor. I forget if it was part of the compressor or separate. Since it was so intermittent did not want to spend the money. Purchased new. Sold 2019 with 90000 miles. 2.4 engine is too risky for major engine issues past 100,000 miles.
 
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