Ac failure, 3 flashes of the light

[Brad Fey]

Ok smarter mechanics i have a 00 gmc yukon.  I just did a rebuild of the ac system.  It comes on and cools down like a champ.  Until I sit still for too long.  Then it shuts off and won't come back on until do a good bit of driving, or it sits overnight.  I have replaced compressor, orifice, and drier.  Condenser coil is clean, charge is good, everything seems to be in order.  All of the vents blow good, and all of the diverters work.  I've tried jumping high and low pressure switches with no results. Clutch fan is spinning great, motor doesn't come close to overheating.

When I press the ac(snowflake) button the light flashes three times then goes out.  

The problem seems to strongly correlate, to times where I'm sitting still, but I guess that could be in my mind.

Any ideas?  I'm going to replace the ambient air temp sensor later today.

[Jsdirt]

Ambient temp sensor isn't going to fix this. You need a good scan tool with live data. If you have a set of gauges, I'd throw them on first and verify system pressure (could be empty or low).

 

In the scan tool you'll need to check ALL parameters, namely something called, "A/C Permission", or similarly worded. If permission is withheld, which it will be with a blinking snowflake button, you'll need to poke around the different parameters and see what's happening. Most common is a failure of the high pressure switch when hot. System will work great until the switch heats up for a while, then it wigs out and starts spitting out random pressures / voltages - the ECU thinks there's no refrigerant when it swings towards zero and locks the system out.

 

Most good scan tools will give a reason for the lockout farther down in the list of info. It will say things like, "pressure" (meaning too low or too high), and "temperature", (thinks it's too cold outside).

[Ravenkeeper]

On 6/18/2021 at 2:05 PM, Brad Fey said:

Ok smarter mechanics i have a 00 gmc yukon.  I just did a rebuild of the ac system.  It comes on and cools down like a champ.  Until I sit still for too long.  Then it shuts off and won't come back on until do a good bit of driving, or it sits overnight.  I have replaced compressor, orifice, and drier.  Condenser coil is clean, charge is good, everything seems to be in order.  All of the vents blow good, and all of the diverters work.  I've tried jumping high and low pressure switches with no results. Clutch fan is spinning great, motor doesn't come close to overheating.

When I press the ac(snowflake) button the light flashes three times then goes out.  

The problem seems to strongly correlate, to times where I'm sitting still, but I guess that could be in my mind.

Any ideas?  I'm going to replace the ambient air temp sensor later today.

On 6/18/2021 at 5:56 PM, Jsdirt said:

Ambient temp sensor isn't going to fix this. You need a good scan tool with live data. If you have a set of gauges, I'd throw them on first and verify system pressure (could be empty or low).

 

In the scan tool you'll need to check ALL parameters, namely something called, "A/C Permission", or similarly worded. If permission is withheld, which it will be with a blinking snowflake button, you'll need to poke around the different parameters and see what's happening. Most common is a failure of the high pressure switch when hot. System will work great until the switch heats up for a while, then it wigs out and starts spitting out random pressures / voltages - the ECU thinks there's no refrigerant when it swings towards zero and locks the system out.

 

Most good scan tools will give a reason for the lockout farther down in the list of info. It will say things like, "pressure" (meaning too low or too high), and "temperature", (thinks it's too cold outside).

 

I had a similar problem with my 91 Skyline, after my compressor seized and I replaced it.  I ended up taking it to the base hobby shop (Kadena AB, Okinawa) and they emptied it, purged it, and refilled it.  They were telling me that I had a "pocket of atmospheric air" in it, from when I put it all back together.