A fan control system for a vehicle cooling system includes forward and reverse relays connected to a microprocessor based timer control. A third relay is controlled by a single temperature responsive switch or thermostat and selects either the high speed or low speed winding of an electric radiator fan or similar engine cooling device dependent on the temperature sensed by the thermostat. The thermostat also provides an input to the timer control to adjust or interrupt preselected timing functions for certain fan conditions. Upon start-up of the engine, the control initiates a first delay period during which the fan is maintained in the off condition regardless of the temperature of the coolant. After the initial delay, a second and longer delay period is initiated to maintain the fan in the off condition provided the sensed temperature remains below a preselected level.