diagnosing AC with VCDS?

No cold air with AC on. I can 'hear' a funny sound in the air vent, not a fan noise but something else. I have VCDS. Any particular values I should look for to know where the problem is?
I see there is a valve in the compressor that is a common failure item.... if it needs gas I have a neighbour who charges his dump trucks ac systems with the auto store cans....
Thanks for any insight.

Thunder Chicken said:

No cold air with AC on. I can 'hear' a funny sound in the air vent, not a fan noise but something else. I have VCDS. Any particular values I should look for to know where the problem is?
I see there is a valve in the compressor that is a common failure item.... if it needs gas I have a neighbour who charges his dump trucks ac systems with the auto store cans....
Thanks for any insight.

Click to expand...

yes vcds can give you some info. It can read current and volts to the compressor valve. From that you may be able to determine if its jammed or not getting power. There are threads on this. I did it 5 years and forgot the address and normal values. If it's stuck power draw will be different. I would not recommend just adding freon in the blind. You can connect Hi Lo press gauges and get an idea. The best way is remove all freon (capture it don'tvent to atmosphere), and install fresh freon by weight. Bottom line no cold air.

I fixed my AC 5 yrs ago in my 2010. It was blowing barely coolish. I replaced the compressor valve. It has blown cold ever sense.

You may have to drop some cash and bring it to competent shop. Don't let them shotgun parts into it. Diganose it, check for leaks.

thanks for the reply. I had done a search and found your thread from years ago, it was helpful.
So, what i've got on VCDS is :
it's been running (ac on at idle in the driveway for some time) no cool air at all.
Refrigerant press: 8.2bar
compressor: no shut off condition
compressor current 0.82a and that stays the same no matter what i do(well goes to 0 when selected off)
compressor load: 3.7nm
OAT: 23°c
temp after evaporator: 26°c
blower is on and working
coolant fans test with output test.
at one point, the coolant cans came on, the pressure dropped from 8.8bar to ~6.

It's looking like the RCV is bad.

I have no shops locally, without a 4 hour drive, or going to a GM dealer, ugh.
i guess i could get them to empty the system, i come home replace the rcv? then go back and get them to recharge the system or can i do it myself at that point with the auto store kit?
there mention of a dryer and replacing it, compressor oil..... guess i have more searching and reading to do.

I had a no cold air situation a couple years ago, was a low charge issue ultimately caused by a leaky compressor nose seal, you may try goosing it with one of the off the shelf ac cans just a few ounces should tell you what you need to know, if it starts to work (pressure jumps to maybe 12-14 bar) while running you have low refrigerant, and should search for a leak, if it stays about the same its probably your RCV.


as for replacing the rcv, you would need to have the system evacuated, replace your parts, then take back to the shop, have them pressure test, pull a vacuum, and charge by weight. I do recommend the uv dye and light, it was how I found my leaky seal

well, as expected, the local GM dealer won't work on 'german cars'. 'We wouldn't know what they used for refrigerant'......
So i put a can of R134 in and it works for now. I haven't hooked up to see what pressures were, the gauge on the can was at ~30psi when i started and didn't change much but it took the whole can.
it's cold for now....
we have a 300 mile drive today, gonna be close to 90° which is very hot for here.

it's worked for a few hours now. I had a few minutes and remembered i had the netbook/vcds in the back from last time...
pressure is now up to 13 bar
compressor current will vary from 0.5 to 0.82a as it needs
compressor load up to 7NM
temp aver evaporator 2°c.

if it works for a while great. putting a can in every now and then will be a cheap fix for a while. only 2-3 more months and there'll be snow in the air anyways.