Method and device to detect the charge level in air conditioning systems

A method for detecting a refrigerant charge in an air conditioning system comprising:

• providing an air conditioning system comprising a compressor, an engine for driving the compressor, a condenser, an expansion valve, an evaporator, a blower including a motor and a fan for blowing air out of the air conditioning system, conduits for coupling together the compressor, the condenser, the expansion valve and the evaporator to define a closed air conditioning system, and a fluid flowing through the conduits, wherein said closed air conditioning system produces a refrigerant charge for the air conditioning system at the system operating temperature and pressure, said method comprising:
• connecting a charge detection device to the air conditioning system;
• operating the air conditioning system to produce cooling air;
• measuring an input temperature and pressure from sensors positioned between the condenser and the expansion valve in the air conditioning system;
• determining an actual sub cooling value from said measured input temperature and pressure;
• assigning a desirable sub cooling value obtained from predetermined sub cooling values stored in a data base in the charge detection device, said desired sub cooling values being selected based on ambient temperature and humidity during said operation of said air conditioning system;
• comparing the actual sub cooling value with the desirable sub cooling value;
• and
• determining the difference between the actual sub cooling value and the desirable sub cooling value during operation of the air conditioning system and if the difference between the values is outside of an acceptable predetermined range, informing a user that the air conditioning system requires service.