On a normal fan center, which contacts can be jumped to activate the condensing unit?

Jumping the R and Y contacts on a normal fan center is the correct method to activate the condensing unit because this action simulates the thermostat calling for cooling. In this scenario, "R" represents the power supply from the transformer, providing 24V power, while "Y" is the cooling relay contact that signals the compressor in the condensing unit to start running. By creating a connection between these two contacts, energization occurs, allowing the compressor to function and initiate the refrigeration cycle.

The other combinations do not activate the condensing unit. R and G would typically activate the fan only without engaging the compressor. Y and W are generally not used together, as W corresponds to the heating circuit, and jumping these would not initiate the cooling sequence. Lastly, G and W would affect the fan and heating operations, respectively, but would not provide the necessary signal to the condensing unit to begin its cooling process. Thus, R and Y is the appropriate and effective choice for activating the condensing unit.