Copyright Goodheart-Willcox Co., Inc. Chapter 32 Residential Split Air-Conditioning Systems 815 10 Thermostat closes at cut-in temperature, energizing Y (cooling) and G (indoor fan) circuits. Residential Split-System Air Conditioning General Sequence of Operation ELECTRICAL SUBSYSTEM Y (cooling) circuit closes compressor contactor. Any other normally closed switches (high-pressure, low-pressure, condensate pan float, timer, etc.) must be closed. G (indoor fan) circuit closes indoor fan relay. ELECTRICAL SUBSYSTEM Closed compressor contactor energizes compressor and condenser fan motor. Closed indoor fan relay energizes indoor fan motor. MECHANICAL SUBSYSTEM Compressor drives the flow of refrigerant through the components of the refrigeration system. MECHANICAL SUBSYSTEM Condenser fan creates airflow over condenser (heat moves from condenser to air). Indoor fan creates airflow over evaporator (heat moves from air to evaporator), through duct system, and into conditioned space. AIRFLOW SUBSYSTEM When temperature falls to cut-out temperature, thermostat opens, de-energizing Y and G circuits. ELECTRICAL SUBSYSTEM Compressor contactor opens, de-energizing compressor and condenser fan motor. Time-delay switch in indoor fan motor circuit activated. ELECTRICAL SUBSYSTEM Compressor and condenser fan stop. Refrigerant stops flowing through refrigeration system. MECHANICAL SUBSYSTEM Forced airflow over condenser stops. Indoor fan continues for a set amount of time. AIRFLOW SUBSYSTEM Time-delay switch opens, de-energizing indoor fan motor. ELECTRICAL SUBSYSTEM Indoor fan motor stops. MECHANICAL SUBSYSTEM Goodheart-Willcox Publisher Figure 32-27. A simplified sequence of operation for a central air-conditioning system.