Superheat vs. Total Superheat
Updated: Sep 12, 2019
Superheat is the temperature increase of the vapor refrigerant from where it turns from the saturated state into a vapor at the evaporator coil until where it exits the evaporator coil. Superheat is not typically used as a charging method for air conditioning systems because there is no port to measure pressure near the evaporator coil. Superheat does not help the technician determine if the refrigerant is in vapor form before entering the compressor. However, a TXV metering device constantly measures the superheat at the evaporator coil to maintain an efficient amount of refrigerant flowing through the evaporator.
Total superheat is a measure of the vapor refrigerant’s temperature increase from where the refrigerant turns into a complete vapor inside the evaporator coil until the refrigerant temperature is measured again near the vapor port.
Total superheat is measured at the outdoor unit of an air conditioning system using the pressure at the large vapor port converted to saturated temperature and the actual temperature on the vapor line within 6 inches from the service port.
Total Superheat is the charging method of air conditioning systems with a fixed orifice. A piston and capillary tube are both considered a fixed orifice metering device. The total superheat method shows if there is vapor refrigerant heading into the compressor. This is because if there is superheat at the location then the refrigerant is still in the vapor state as it enters the compressor. The other reason that total superheat is used is because of the easy access to the ports at the outdoor unit.
See the pictures below for examples of Superheat and Total Superheat.
Check out our book “Refrigerant Charging and Service Procedures for Air Conditioning”.
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Author: Craig Migliaccio
About the Author:Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 15 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel