The first question is: Is the system functioning or not? You could have warm air in the car with a functioning, cold air conditioning system -- if you have a temperature blend door problem in the car. Check the lines to the accumulator if you can - see if they are cold after running the AC a bit. Does the compressor turn on and off - cycling? Quickly? Slow? Not at all? Quick suggests low charge, on for a while then off seems normal, not at all seems like a system electrical issue. You could have a cycle switch issue, a high pressure cut off switch issue, a compressor coil issue.