When you go to the doctor for whatever reason, the first thing the nurse does is measure your vital signs, which include body weight, blood pressure, heart rate, body temperature and these days, blood oxygen level. There is a “normal” range for these body functions and any deviation from normal could indicate some illness.
Several years ago, it dawned on me that operating heat pump system “numbers” could be referred to as the system vital signs. As the heat pump “doctor”, the service tech knows what the acceptable range of numbers should be and can diagnose an “illness” when one or more of the numbers is outside the range.
The primary vital signs are 1) saturated evaporating and condensing temperatures 2) superheat and 3) subcooling. Those numbers along with indoor and outdoor temperature values allow us to analyze the system operation and troubleshoot an issue.
