Condensing Unit And Evaporator Not Working

■     Check the settings on the thermostat. Is unit turned on and is the temperature high enough to be calling for the unit to operate.

■     If unit fails to come on, turn fan control switch of the sub-base to the constant run position. If the fan comes on, low voltage is present in the system. If it doesn’t come on, there is no low volt­age in the system. Check at the transformer for secondary voltage. If not present, check the primary.

No primary voltage —        Check fuse that supplies the unit.

No secondary voltage —    Bad transformer.

Both primary and secondary voltage present – Check at sub-base of thermostat for 24 volts.

Voltage present at sub-base — Replace sub-base and thermostat.

Voltage not present at sub-base — Control wiring from transformer to thermostat defective.

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