yepodm

My 2007 Audi A8L was in an accident, had to replace front end clip including radiator and ac condenser. Went to recharge the AC and the technician told me that AC compressor is not engaging. AC blows warm air, not a single indicator that it's being cooled. High and low pressure lines are hot to the touch. There was no damage to the motor at all, just the front clip. Replaced the High Pressure Sensor (G65) just in case, compressor is still not engaging. Checked VCDS and it shows no errors. Checked the fuses for the AC, all good. Anyone had similar issues? Anyway to see in VCDS if the compressor is engaging? Because I am ready to do the painful task of replacing the AC compressor.

Thanks!

ltooz_a6_a8_q7

Do a simple check with ac manifold, to recharge correctly, you must evacuate all air out of the system.

https://www.dognmonkey.com/audi/what...ac-system.html

Cheers,
Louis

yepodm

Yes, the technician evacuated the air. I checked the the system for pressure, followed the instructions in the linked video, high side is around 50psi and low side is around 10psi.

mcs

Mine had an issue where the compressor didn't come on last summer.

It was the oddest thing, but if you drove for a bit at a very heavy throttle, it would engage and activate for the rest of the journey. No idea why.

Eventually it un-broke.

Mike

ltooz_a6_a8_q7

The only thing before anything else is the temperature sensor in front of the radiator, the accident may damage it.
Cheers,
Louis

snapdragon

What a useless mechanic. As with most modern/decent cars, the compressor doesn't engage like the old cars where you see the centre of the pulley turn or stop. It is a breakaway pulley that only visibly turns if the compressor seizes. The compressor is running all the time as it is a variable displacement compressor that shortens/lengthens the piston strokes (displacement) by moving the swashplate with a solenoid.

yepodm

Mechanic filled up freon only halfway and said that compressor doesn't engage. Does it need to be filled up fully in order to have cold air coming through? Disclaimer, I am myself is a noob when it comes to AC.

ltooz_a6_a8_q7

If you come here to ask for advice and you and your mechanic can't even follow simple instructions, you don't deserve having cold air in a hot days inside a wonderful A8 LOL.

yepodm

Fixed the problem. Disclaimer, I never dealt with AC systems in my life. Today I was ready to replace the compressor, took the bumper off and was about to put the car into service position. Out of curiosity I started trouble shooting the electrical, checked the voltages on the connector that plugs in to the solenoid on AC compressor with Econ mode ON and OFF, I got 5V on OFF and around 12V on ON. I unplugged the pressure sensor (G65) and fans started to spin at full speed. Applied voltage to the solenoid on the AC compressor and listened if it was engaging, it was. Meanwhile the solenoid engaged I heard the AC compressor change in noise, something was definitely working on the inside. Also I knew that my AC line right after orifice was always getting really cold on one side and warm on the other side. With all this observable indicators my intuition told me that the AC compressor was most likely working fine and I was missing something obvious. So as a last resort I followed my intuition and went to O'reilley and bough a can of freon. Came home, started adding freon into the system and just like that the cold air started blowing inside the car. I already paid the mechanic for adding partial freon, he told me to come back after when I fix the AC compressor and he will evacuate and recharge the AC for free. So now I will go back to the mechanic, I will educate him on how the compressor actually works thanks to snapdragon, and I will ask him to evacuate the system and refill it again for free since I have not evacuated the air.

Thanks to all who contributed!