How to Properly Check and Adjust the Refrigerant Charge

“Back in the day” when cap tubes and pistons where the most popular metering device, a technician could check and adjust the charge with suction superheat, get it “beer can cold” and call it a day.

Now that all the American Standard product line is 13+ SEER with all TXV metering devices it is important to know how to properly check and adjust the charge. Suction superheat will only verify if the TXV is metering correctly or not. Liquid subcooling must be checked as well to accurately diagnosis whether you have an undercharge, overcharge or a restriction. With the combination of these two readings, plus airflow (cfm) and your pressures a technician can diagnosis just about any situation he or she comes across.

To check Liquid Subcooling: A technician must start with an accurate set of gauges installed on a running system. Record the liquid pressure. Using a pressure/ temperature chart (PT chart) convert that pressure into the corresponding temperature for that given refrigerant. Next, using a good quality clamp on type thermometer check and record the temperature of the liquid line. Now subtract the lower temperature you recorded from the liquid line from the higher temperature you recorded from the PT chart. The result is your liquid subcooling.

Example: Your liquid pressure is 210psi which, converted to temperature is 105º. The liquid line temperature measured with your clamp-on thermometer is 95º. This is a difference of 10º. Therefore your liquid subcooling is 10º. Simple!

As with anything else in this industry, it takes practice. If you get stuck or confused on your readings, or have any other problems, please do not hesitate to contact us at service@americanairdist.com.