When residential air conditioning systems were first installed in the 50’s & 60’s the procedures and instruments to check for proper operation were not that sophisticated.
The Key Element to check the operation were gauges to test the Refrigerant Charge on the system. This consisted of a Port to check the Suction Line (larger insulated line) and the Liquid Line (smaller copper line) to give you Pressures based on the Outside Temperatures to indicate the Proper Charge. If Suction Line Pressure was too Low you would have to add R-22 Refrigerant to system.
In this era when air conditioning was becoming commonplace a hands on method for homeowners was called “Beer Can Cold”. You can put your hand on the Insulated Suction Line and if it felt like a can of beer that was cold chances are the Refrigerant Charge is satisfactory.
Since Air conditioning has become commonplace the procedure for checking refrigerant charges has become a lot more sophisticated.
The Methods that are now used are called SUPERHEAT and SUBCOOL.
To determine SUBCOOL you attach gauges to liquid line service valve and take a pressure reading. You use a Pressure/Temperature Chart to convert this pressure to the Saturated Condensing Temperature of the Refrigerant. Then you attach a Digital Thermometer to the Liquid Line. This Temperature that you read should be Lower than the Saturated Condensing Temperature. The Difference between the measured Liquid Line Temp and the Saturated Condensing Temp is the Liquid Line SUBCOOL.
With this method it can determine if there might be dirty filters or insufficient air flow or possibly dirty condensing coil.
As you can see this Modern Method of Checking the Refrigerant Charge for your Air Conditioning System is not for an average Homeowner.
The Homeowner can still use the old school BEER CAN COLD method by feeling the suction line to see if it is Cold. Hopefully with this Cold Feel it tells you you’re a/c I working well! Nobody likes a Warm Beer!