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A/C problems


blue98ls1

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03 Chevy Avalanche 2500. Started the truck yesterday, everything was fine. Took it about 10 minutes away and the A/C stopped working. I messed with it for a while yesterday and made no progress so I brought it into work today.

 

Here's what I know... If you disconnect the battery, A/C works. If you leave it sit over night. A/C works. It will stop working after about 5-10 minutes, it will not come back on until one of the above happens. System already had dye in it, no visible leaks. We discharged/recharged the system, no change. Its not a relay. Its not the pump. Compressor clutch kicks on/off fine during the time its working.

 

We are kind of thinking a pressure switch or control unit. Obviously will try pressure switch first. Anyone have any thoughts?

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Hook up a scan tool and be sure the compressor is commanded "on". Many newer cars have to "see" multiple criteria to allow the compressor to run. For instance:

 

DIAGNOSTIC AIDS

A/C compressor clutch will not engage under the following conditions:

The A/C high side line pressure is over 2957 kPa (429 psi) .

The A/C low side line pressure is under 151 kPa (22 psi) .

Throttle angle is at 100 percent .

Engine speed is more than 5500 RPM .

Engine coolant temperature (ECT) is more than 121°C (250°F) .

Ambient air temperature is less than 5°C (40°F) .

 

Just because you know these conditions don't exist doesn't mean the PCM isn't "seeing" them. For instance, a bad coolant temp switch that is registering too high can cause the compressor to not engage (and the gauge can still read normal). Yes, a bad high/Low pressure switch can also be the cause, but a quick look with the right tool can save a lot of hassle.

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Assuming it wasn’t low on refridgerent (all you said was that you evac and recharged it, so I assume it wasn’t low to begin with), it definitely sounds electrical. Is this vehicle auto climate control? I’d bet it is. Follow along with what Craig said above, and use your tech2 to see if there are any DTCs in the ECM or the HVAC control module under the “Body” section. Then use the live data to see what sensor is out of range, it sounds like one of the temp sensors or maybe the sunload if it isn’t the control head itself.

 

Just don’t throw parts at it. Pressure sensors are not common. It wouldn’t surprise me with a truck that age to have an issue with a slipping shitty compressor clutch that won’t stay engaged.

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Assuming it wasn’t low on refridgerent (all you said was that you evac and recharged it, so I assume it wasn’t low to begin with), it definitely sounds electrical. Is this vehicle auto climate control? I’d bet it is. Follow along with what Craig said above, and use your tech2 to see if there are any DTCs in the ECM or the HVAC control module under the “Body” section. Then use the live data to see what sensor is out of range, it sounds like one of the temp sensors or maybe the sunload if it isn’t the control head itself.

 

Just don’t throw parts at it. Pressure sensors are not common. It wouldn’t surprise me with a truck that age to have an issue with a slipping shitty compressor clutch that won’t stay engaged.

 

It's dual climate control, yea. I drove it around when I was pretending to be Anthony a few weeks ago.:dumb:

 

For what it's worth Tina, it didn't work for me either from the moment I started it up.

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Assuming it wasn’t low on refridgerent (all you said was that you evac and recharged it, so I assume it wasn’t low to begin with), it definitely sounds electrical. Is this vehicle auto climate control? I’d bet it is. Follow along with what Craig said above, and use your tech2 to see if there are any DTCs in the ECM or the HVAC control module under the “Body” section. Then use the live data to see what sensor is out of range, it sounds like one of the temp sensors or maybe the sunload if it isn’t the control head itself.

 

Just don’t throw parts at it. Pressure sensors are not common. It wouldn’t surprise me with a truck that age to have an issue with a slipping shitty compressor clutch that won’t stay engaged.

 

It was not low. It does have climate control.

 

Used our scanner and it only has a body code for the recirculation circuit. B0229.

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It was not low. It does have climate control.

 

Used our scanner and it only has a body code for the recirculation circuit. B0229.

 

Recirculation door won't cause the A/C not to run. As Cordell mentioned, check the live data on the Tech II for:

 

The A/C high side line pressure is over 2957 kPa (429 psi) .

The A/C low side line pressure is under 151 kPa (22 psi) .

Throttle angle is at 100 percent .

Engine speed is more than 5500 RPM .

Engine coolant temperature (ECT) is more than 121°C (250°F) .

Ambient air temperature is less than 5°C (40°F) .

 

If these sensors are sending an incorrect value to the PCM, no A/C. I would be most suspect of the last two being out of range based on your comment that the A/C will work initially, then shut off. But that is just a guess.

 

Even though everything seems normal, if the sensor is bad/sending an incorrect value, the PCM does believe whatever it is told!

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A/C line pressure is fine. All engine sensors appear to be normal. With the scanner if you command it to work, everything works. Command state other wise says "Withheld". When you turn on the A/C with the button on the control unit it flashes for a second on the screen that you hit the button but goes right back to "off". All sensors on that command screen appear to be working. I am sure someone with more knowledge of this scan tool could probably figure this out fairly quick.
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I will defer to Scott on the Tech II as I have had/used "generic" scan tools.

 

If the ability to turn on the compressor is "withheld", it would leave me to believe the PCM is still seeing/not seeing something it needs to allow it to run.

 

 

"Open the pod bay door Hal", "I'm sorry Dave, I can't do that"

Those days have arrived!!!

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I will defer to Scott on the Tech II as I have had/used "generic" scan tools.

 

If the ability to turn on the compressor is "withheld", it would leave me to believe the PCM is still seeing/not seeing something it needs to allow it to run.

 

 

"Open the pod bay door Hal", "I'm sorry Dave, I can't do that"

Those days have arrived!!!

 

I am kind of thinking the actual control unit is bad. The little snowflake emblem stays on during all of this showing the A/C is on instead of flashing or turning off. I also figured out my rear defrost is doing the same shit. :fuuuu: I swapped out pressure switches with a friends that are known good and nothing changed. So ruled those out.

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I will defer to Scott on the Tech II as I have had/used "generic" scan tools.

 

If the ability to turn on the compressor is "withheld", it would leave me to believe the PCM is still seeing/not seeing something it needs to allow it to run.

 

 

"Open the pod bay door Hal", "I'm sorry Dave, I can't do that"

Those days have arrived!!!

 

You would be correct sir. Not much more I can do over the internet.

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So i bought another control unit as the one in the truck looked pretty beat up anyways. New unit shows a snowflake with a line through it, which is new... old one just had a snow flake. This did not fix the problem obviously since its showing the line through the snowflake.

 

Messed around a little more with the scanner. I still have no idea what isnt working. Its like something isn't sending the signal to turn it on and i have no idea what as everything i have replaced/tested works. Considering the A/C works perfect with a manual input guessing not wiring, compressor etc... about to send it to a shop as i don't know what else to replace/try.

 

20190616-101929.jpg

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