You need to remove that part of the panel on the condenser where the electrical wiring enters. It would be wise to shut off the power to the condenser circuit first. Inside the panel you will find an electrical contactor (relay) w/thermostat type wires connected to it. Most contactors inside these condenser units are low voltage (24 volts), some are line voltage 120 or more volts. If this contactor has a 24 volt coil (the specs are printed on the contactor), then the power is independant of the condenser power source at the disconnect switch and you can safely check for power to this contactor. The wires from the thermostat go to the air handler fan center relay and the 2 wires from the outside condenser also connect to this fan center relay. With the thermostat set to the cool position and the thermostat set to a temperature below the actual room temperature, power (signal) should be present at the condenser contactor. The newer digital thermostats have a built in compressor on delay(sometimes as much as 5 minutes), so that the signal may not be present immediately to the contactor. Check for power at the contactor coil. If there is power at the contactor coil, then suspect a bad contactor coil. If there is no power at this coil further trouble shooting is necessary. For instance, do the two thermostat type wires entering the condenser connect directly to the contactor coil or does only one wire connect straight to the coil and the other wire lead to a pressure actuated switch (prevents the compressor running if the refrigerant charge becomes low) and then back to the contactor coil. Some air handlers also have a (water)float switch in the air handler or a (water) float switch in the condensate pump that prevents the outdoor condenser from running when the condensate water gets too high as would occur if the condensate pump fails or the condensate tray at the evaporator coil becomes blocked. In either case the signal to the contactor coil would be interupted and no voltage to the contactor coil would be present.
· 1 decade ago