I turned on the A/C, and the car blows hot air. I recharged the system and it showed it was full, but the A/C compressor would not engage, or turn on. I disconnected the low pressure switch on the accumulator and it turned on. I reconnected it to the switch and it still wouldn't turn on. I replaced the switch, bought a new can of freon, but to no avail, the compressor still doesn't turn on. Any suggestions? The system is retrofitted to 134A.