Condenser fan control system

Abstract

A method of controlling a fan for cooling a condenser in an air conditioning system is provided. A compressor serves to drive a refrigerant around a fluid circuit which includes the condenser. The duty cycle of the compressor is measured over a period of time to determine a utilisation ratio which reflects the demand on the air conditioning system at that time. The fan is driven at a speed which is no lower than a minimum fan speed which is associated with the calculated utilisation ratio and ambient temperature. Therefore, the demand on the system is determined and exploited without any additional pressure sensors.

1 . A method of controlling a cooling fan in an air conditioning system which comprises a fluid circuit having a compressor and a condenser cooled by the fan, the method comprising measuring the ratio of the time that the compressor is active to the time that the compressor is inactive over a predetermined period of time, and operating the fan at a speed which is no lower than a predetermined minimum fan speed associated with said ratio. 
     
     
         2 . A method according to  claim 1 , wherein measuring said ratio includes sensing an electrical current supplied to the compressor. 
     
     
         3 . A method according to  claim 1 , wherein operating the fan includes obtaining the predetermined minimum fan speed from a lookup table. 
     
     
         4 . A method according to  claim 1 , wherein the air conditioning system further comprises a temperature sensor located in the volume to be cooled by the system. 
     
     
         5 . A method according to  claim 1 , wherein the air conditioning system further comprises a temperature sensor located in the fluid circuit downstream of an evaporator. 
     
     
         6 . A method according to  claim 4 , further comprising the steps of:
 activating the compressor in response to the sensed temperature exceeding an upper temperature threshold; and   deactivating the compressor in response to the sensed temperature falling below a lower temperature threshold.   
     
     
         7 . An air conditioning system operating according to the method of  claim 1 . 
     
     
         8 . A tractor comprising an air conditioning system according to  claim 7 , wherein the fan also serves to cool an engine cooling radiator and/or a oil cooling device.