AC Compressor running but no cold air?

how do you know if it is actually the ac compressor that is at fault ( perfectly good ac compressor from a wreckers /junk yard are available to suit your car at around 70% saving on a new unit )
there are several safety switches in the system that prevent the ac compressor from working
the main reason for ac failure is loss of gas from a leak
next while you can replace the ac compressor yourself , if you have the tools and the know how you will still need a vacuum pump to vacuum the system down to remove the air and a set of gauges to get the right pressure when regassing
first move is to go to an ac specialist shop and have it properly diagnosed and a quote
Then you will and an idea how much you will have to save to get it fixed

What you need to do is check the air gap in the clutch, if it is to large it will not engage, it can also be adjusted by removing shim washers or removing some thickness off a Washer....

Is the compressor running ? What are the low and high pressure readings ?
Are the radiator fans running ?
Is one ac line cold and one hot in the engine compartment.

You will need to know if the compressor is working when it blows hot air to proceed. It could be an electrical problem, a blend door problem, or the a/c clutch on the compressor.

CHECK AC COMPRESSOR CLUTCH COIL WIRE CONNECTOR HOOK UP.IF AC COMPRESSOR CLUTCH COIL WIRE CONNECTOR HOOK UP WRONG OR WIRE HAS A SHORT IT WILL BLOW THE ECM FUSE AND AC COMPRESSOR FUSE.CHECK FUSES AND AC COMPRESSOR WIRES.

I would check the following possibilities:
1. Is compressor clutch working? - You need to do this when the ac is blowing hot air only - locate compressor drive pulley on engine - rubber belt wraps around it. Start engine and set to max ac. When the ac is blowing hot air, look at the center of the compressor drive pulley using a good flash light - watch it for a while, it should be spinning with the pulley - this means the compressor is engaged. If not, the compressor is not engaged. If your ac is blowing hot air, then the compressor should be engaged and running (trying to cool). If it is not engaged, then your compressor clutch is probably going out. Could be low voltage to clutch, but more likely the clutch is worn out and only working some of the time. Note: if working normally, the compressor clutch will engage and disengage in cycles- but the air should always be cold. If clutch is bad, compressor would need to be replaced (sold as one unit). This is tricky to diagnose and could take some time - you need to do it when ac is blowing hot air but set to max cooling.

2. Low on refrigerant or refrigerant has moisture in it? If your ac blows cold initially after being off for a while, then heats up, and continues to regularly cycle back and forth between hot and cool air, then the system may be low on refrigerant or the refrigerant may have moisture in it that is freezing and restricting refrigerant flow. An a/c shop can check refrigerant level and even replace refrigerant if moisture is suspected.

Could be other issues, but I would start with these.

Good luck

high and low pressure swich try putting freon in it

You would have to measure the pressure to determine if it's pressurized correctly. The compressor won't run if it's low.
What happens when you push the a/c button? Can you hear/feel the compressor kick in? It seems like in most cases it's the compressor itself or the compressor clutch that goes. It's way too common in vw's...

This is very vague. Is the blower motor working (can you hear blowing inside?), is it blowing but it's hot? Can you hear the compressor running (open your hood and listen if something is kicking on and off). AC is so complex. It could be as simple as a freon leak or as complex as a compressor, hose, accumulator etc.

/Does the compressor kick in compressor or the compressor clutch might be shot