When should I take my actual and target superheat/subcooling measurements?
Superheat and subcooling readings must be taken when the system is in a steady state condition. Typically a residential system will be at steady state after ~10-15 minutes, but can be longer. Turn the system on and set the thermostat low to ensure that the system doesn’t turn off during your testing. Once the system’s temperatures and pressures are no longer noticeably changing the system is at steady state. All measurements must be taken at the same time. In other words, wet bulb temperature and outdoor dry bulb temperature must be taken within a short amount of time from the actual superheat or subcooling reading to obtain valid measurements. Conditions can change that affect your target superheat subcooling number by the minute. For example, you might take a dry bulb reading outside of 75°F at 1:00 pm. You come inside, take a wet bulb reading, then look at the manufacturers target charts, and finally set up your pressure and pipe temperature measurements. By 1:30 pm the reading outs
