A fan relay is an electromagnetic switching device that controls power delivery to the blower motor based on thermostat demand or temperature sensor input. This relay allows low-voltage control circuits to safely switch the high-amperage circuits powering the blower motor without direct thermostat contact. Fan relays enable automatic fan operation modes and sequencing control in forced-air HVAC systems.
Operational Specifications
Standard fan relays switch 24V AC coils to control 120V or 240V power delivery to blower motors drawing 10-20 amps. Relay contacts are rated for 25,000-50,000 cycles, equivalent to 5-10 years of typical residential operation. Response time is typically 50-150 milliseconds, providing rapid fan engagement when heating or cooling is demanded.
Control Functions
Fan relays enable three operational modes: automatic operation where the fan runs only during heating or cooling cycles, continuous operation for constant circulation, and thermostat-controlled variable staging. Multiple relays can be installed for multi-stage cooling systems or variable-speed motor control. Failed fan relays result in blower inoperability and complete loss of air circulation until replacement occurs.