The air circulation fan associated with a radiator of some machines may include an automatic reversing purge cycle that is utilized to dislodge material from the radiator and/or intake screen of the cooling system housing. The purge cycle is locked out when a person may be in the vicinity of the air intake screen of the machine. A controller determines that a person may be in the vicinity of the air intake screen when the machine is idle stationary, such as by determining that a parking brake is engaged. By locking out the purge cycle during machine idle stationary conditions, the risk of blowing dislodged dirt and/or debris onto a person, who may be servicing the machine or accessing an operator station, can be avoided.