A/C Compressor not kicking on
 

My dad replaced a bad bearing on my ac compressor. We didn't have to disconnect any hoses and didn't disconnect any wiring harness. We were able to pull it out a few inches to swap bearings. When it was done, the compressor kicked on and worked fine. We replaced a thermostat and tested the ac and heat and everything worked fine. My heater gets hotter now, before it wasn't getting hot enough. Later my dad replaced an idler pulley and alternator belt because my belt was frayed. My dad unplugged the big wiring harness and a small 5v harness near the alternator then reconnected when done. The battery was connected when he did this. After installing the new belt and idler pulley. I pulled the car outside, which is 36 degrees outside. Turned on the A/C and the compressor wouldn't turn on. When my dad was testing it in a heated garage he said he had to press hard on the a/c switch for it to turn on. during the summer I noticed a few second after pressing the a/c switch the compressor kicks on. The light illuminated for a/c when I switch it on, but the compressor doesn't click and the clutch does not engage. Does anyone know how to find out what's not working?

Well I pulled out the relay, turned on the ac, then plugged the relay back in while on. It sparked, the clutch engaged and the air works again. Perhaps the relay was stuck on.