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hey guys, i have a 05 ctsv i just bought with 100k miles. love the car, i’ve been wanting one for a long time. only bad is that the ac doesn’t work. i always get the “service ac system” message. brought it to a guy at the shop who’s been all around it and we can’t find anything. topped the freon, replaced the high pressure switch and the pigtail for it, checked almost all of the wires... nothing. when he resets the code i’ll get ac for a couple of minutes then it kicks right back off. it’s winter in alabama right now so it’s not a big problem but i definitely need to figure something out before the summer when i’m burning alive in the black interior.
 

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'05 CTS-V
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"Topped the freon" meaning what? Did you put an actual gauge manifold on it, check high and low side pressures, measure ambient and outlet vent temperatures, etc?
 

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You might have a hole developing in one of the lines. That is how my troubles last summer started...

Go to harbor freight and get the UV led blacklight, its fairly cheap but very bright. Take off the low pressure (big one) fill cap and shine it the UV light on it (in the shade), if you see neon green then you have UV dye in your system. ((If you dont then have your AC guy add some dye or add freon with dye in it yourself)) Then run your A/C and check under both fill caps, those schraider valves go bad sometimes, put a little A/C oil on those valves. If the A/C oil bubbles up there then thats your leak, if not go under the car. There are 2 lines that go under the engine from the compressor (on the passenger side) to the condensor coil in front of the car. If you see green under your car with the UV light splattered everywhere then you indeed have a leak.

Lastly after you have added the UV dye, charged the system and double checked everywhere you need to check the evaporater coil for a leak inside the cabin. You can check for a leak there by buying a cheap $20 HFC freon leak checker on Amazon. The evaporator water drain tube is by the driver's right foot. Pull the tube off and stick the leak checker there. If this is the source of your leak then you will need to start saving because your dash needs to come out to replace the evaporator.

Hope this helps or at least keeps you from buying a new compressor prior to you finding a leak in your lines.

Links:
https://www.harborfreight.com/uv-blacklight-flashlight-63931.html
https://www.amazon.com/Refrigerant-...id=1547473569&sr=8-3&keywords=hfc+leak+sensor

The schraider valves are oddly large on our cars. They can be found in stock at NAPA. Bring the old one there as they will initially sell you the regular small one.
 
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