first.octopus

I got a 2008 A6. The AC stopped working a few months ago. It is getting warm here in southern California. It is time to get it fix. I have read so many posts in this forum regarding to AC issue. I found most people were talking about Heater control unit got stuck so that it blew hot air regardless the temp setting.

Before the AC completely stopped working, I could feel the air from the driver side vent was slightly cooler than the passenger side. Now, both sides have no cold air anymore.

I have done some troubleshooting myself. I check the temperature on the AC vent using a thermometer with different temp setting.

When setting to LO, it is about 95-97 F.
When setting to ECON, it is about the same as LO (maybe a couple degree high).
When setting to HIGH, the temperature was going up (130+). Then setting back to LO, the temperature return back to 95-97 F. The heater control valve seemed to be closing. Is it closing completely? I can’t tell.

My next observation was trying to hear the click sound when the compressor was turn on. But I could not hear that click sound. I think it may be because the engine and the fan noise were too loud. But I found that the A/C line was getting cold; but not that cold. This led me to believe there may be not enough Freon in the system or there is a leak. Not sure!

My next step would be trying to determine how much Freon is in the system. Is there any DIY way to find that out before I bring the car to the shop?

Any advice or comment would be greatly appreciated.

4Driver4

Sounds like a leak.
I'd take it somewhere for diagnosis.

dzywicki

You can use one of the off the shelf self charge cans from any autostore or Walmart to check the pressure on the low side. This is a very rudimentary way to check freon level. To get the system charged correctly you need to check the high side pressure and low side pressure. The low side gauge that comes with the self charge cans, may give you a hint to having any freon in the system. If your compressor is not working the pressure gauge will read pretty low. If the compressor kicks on, you will see the pressure gauge rise and then drop when the compressor kicks off again. As a very simple self diagnosis, you can add freon to through the low side port to see if the compressor will kick on. If doing this method, I would not add more than 1 can to try to get the compressor to kick on. If the compressor does kick on, it means you have a leak but the other pieces are functioning. If the system has lost all freon, then oxygen got into the system and you will need a complete evacuation and replacement of the receiver-drier.
The only way to know exactly how much freon is in the system, you need to evacuate the entire system (capture the freon), vacuum down the system to -30 psi, then refill with the correct amount of r-134. Unless you have a vacuum pump and full gauge set, you will not be able to do this yourself. A/C can be very tricky to mess wwith and you must have the right equipment to get it right. If you don't have the equipment, take it to a shop.
Start with adding a can through the low side, checking low side pressure, try to get the compressor to kick on and go from there.

first.octopus

Found a video from youtube, it is called "Step by Step A/C Pro® Instructions". Got a 20 oz can of A/C Pro (with hose and gauge) from Autozone. Following the steps, I confirmed there was very low refrigerant in the car. Re-filled the refrigerant and A/C is working again. After the refilled, the can still have about 1/3 refrigerant left which is expected. 20 oz refrigerant is more than the A/C system can hold.