Data Aire air-cooled condensers utilize a fan speed controller. On single fan units this is the only means of control.
Multiple fan condensers are provided with fan speed control on the first motor (nearest the header.) The fan speed control is pre-programmed and there is no need for field adjustment. The header fan will cycle with the head pressure.
Units with R-410a the starting pressure is 320 PSIG with the fan at full speed 400 PSIG. Units shipped with R-407c the starting pressure is 220 PSIG with the fan at full speed 285 PSIG.
When the condenser heat load exceeds the output capacity of the fan speed controller fan, the second fan is turned on to full speed in conjunction with the fan speed controlled motor and the fan speed controlled motor modulates to a new start pressure. This allows the condenser load to be modulating by the cooling effect of two fans instead of one.
Additional motor (subsequent to the fan speed control operated motor) on multiple fan heat exchangers are cycled by ambient sensing thermostats.