A method of controlling an air conditioning system having a cooling mode and a free-cooling mode, comprising: operating the air conditioning system in the cooling mode including: circulating a working fluid and a refrigerant through an evaporator of the air conditioning system in separate fluid communication with the working fluid and the refrigerant; circulating the refrigerant through a compressor; and bypassing a refrigerant pump; measuring, via a first temperature sensor, a first temperature of ambient outside air at a condenser; measuring, via a second temperature sensor, a second temperature of said working fluid exiting said evaporator; calculating a difference between said first and second temperatures; comparing said difference to a predetermined value; determining an available cooling capacity for operating the air conditioning system in the free-cooling mode; operating the air conditioning system in the free-cooling mode, including bypassing the compressor, if said difference is greater than or equal to said predetermined value and the air conditioning system has the available cooling capacity; and operating the air conditioning system in the cooling mode if said difference is less than said predetermined value or the air conditioning system does not have the available cooling capacity; and continuously monitoring the first temperature and the second temperature for the calculation of the difference, the calculation being used as a factor in switching the air conditioning system between the free-cooling and the cooling modes. operating the air conditioning system in the cooling mode including: circulating a working fluid and a refrigerant through an evaporator of the air conditioning system in separate fluid communication with the working fluid and the refrigerant; circulating the refrigerant through a compressor; and bypassing a refrigerant pump; circulating a working fluid and a refrigerant through an evaporator of the air conditioning system in separate fluid communication with the working fluid and the refrigerant; circulating the refrigerant through a compressor; and bypassing a refrigerant pump; measuring, via a first temperature sensor, a first temperature of ambient outside air at a condenser; measuring, via a second temperature sensor, a second temperature of said working fluid exiting said evaporator; calculating a difference between said first and second temperatures; comparing said difference to a predetermined value; determining an available cooling capacity for operating the air conditioning system in the free-cooling mode; operating the air conditioning system in the free-cooling mode, including bypassing the compressor, if said difference is greater than or equal to said predetermined value and the air conditioning system has the available cooling capacity; and operating the air conditioning system in the cooling mode if said difference is less than said predetermined value or the air conditioning system does not have the available cooling capacity; and continuously monitoring the first temperature and the second temperature for the calculation of the difference, the calculation being used as a factor in switching the air conditioning system between the free-cooling and the cooling modes.