I am on a no ac service call where the thermostat is blank. I have no 24 volts at the stat. I first notice that the air conditioning systems 3 amp fuse blown. Therefore, I troubleshoot the HVAC system's low voltage wires. The 24 VAC compressor contactor test to ground. Next, I replace the shorted contactor and test the ac system. Unfortunately, I wired the system out of phase and the blower spun backward. After fixing the phasing the system started cooling.