A/C Compressor Won't Kick On

don't by pass the system with an on off switch for the compressor. If your system hits too high of a pressure it needs to cut in the fun/or cut out and if it high too low of a pressure it needs to cut out as well if not you'll be buying a new compressor. I am not sure exactly how this system is run. However almost every system i have run across has a low pressure switch that prevents the clutch from engaging. Check for power and grounds at this switch. If you can engage the clutch by jumping the connector then the switch is most likely faulty. The high pressure switch is there to kick and electric fan in..providing the car has an electric can. Fan forces air through the condenser in an effort to reduce pressures in the system (cooling the R134A). Check for leaks with Nitrogen............it is clean and dry so no contaminates are introduced to the system. 300 lbs is what i regulate the bottle to while testing....then just soap and water at every connection. The hardest leak to find is the seal right at the shaft of the compressor cause the clutch is in the way. ummm....if you have gauges hooked...a good rule of thumb is the high side pressure should be running at two time ambient temperature plus or minus 10%. once you have a proper charge in.
A wiring diagram would assist you tonnes while chasing power and ground for the a/c. To charge the system you need a vacuum pump which needs to run for a minimum of 15 minutes............once thats complete you can add refrigerant oil (1 to 2 ounces) the vacumm draws the oil in. Then charge. I don't recommend using Redteck or propane. R134A is the best to use providing the system was designed for it.........older cars usually have R12 which can be easily retrofitted to R134A. I don't know how much help my knowledge of A/C is gonna be for you with your problem, but i hope it helps you find some solution.