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Without accessory economizer — Upon a request for cooling from the space thermostat, terminals Y1 and G will be energized with 24 v. As a result, the indoor-fan contactor (IFC), outdoor-fan contactor (OFC) and Compressor contactor no. 1 (C1) will be energized, which in turn will energize the indoor fan, outdoor fan and Compressor no. 1, respectively. If the space thermostat calls for a second stage of cooling by supplying 24 v to Y2, Compressor contactor no. 2 (C2) will be energized, thus energi