Superheat vs. Total Superheat
- Craig Migliacco
- Apr 5, 2019
- 2 min read
Updated: Mar 2
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”.
The full outline is available at https://www.acservicetech.com/the-book
If you have already purchased our book, be sure to tell local HVACR Instructors about our book and what you think of it. We would love to get the book into the hands of the next generation of HVACR Technicians!
Published: 4/5/2019
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
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This is a very clear and accurate breakdown of superheat versus total superheat! Understanding where to take the measurements and how it applies to fixed orifice systems compared to TXVs is so crucial for any technician out in the field. Troubleshooting HVAC systems can get really intense and definitely drains your brainpower after a long day. Whenever I finish checking a complex system or studying these guides, I usually like to take a complete mental break and play a quick minigame to unwind before moving on to the next job. Thanks for the solid technical tips!
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Duidelijk uitgelegd! Het onderscheid tussen gewone ‘superheat’ (verdampingstemperatuur) en ‘totale superheat’ is essentieel, zeker voor monteurs die met expansieventielen (TXV) of fixe ringen (capillair/piston) werken. Fijn dat je benadrukt dat totale superheat de juiste methode is voor systemen met een vaste orifice – dat scheelt verwarring in de praktijk. De foto’s in het artikel maken het inzichtelijk, en je punt over het meten van de damp bij de servicepoort is echt een praktische tip. Ook sterk dat je waarschuwt dat gewone superheat (alleen bij de verdamper) geen garantie geeft over de toestand van het koelmiddel bij de compressor. Goede aanvulling op jouw boek!
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A well-structured and technically clear explanation of a topic that is often confusing for many learners and technicians. The way you broke down superheat vs total superheat makes it much easier to understand real HVAC system behavior and troubleshooting. I recently came across a similar discussion on a review blog, and it offered an interesting perspective as well. I also found it useful to cross-check concepts using tools like https://www.servexpertpro.com/, which helped reinforce the practical understanding behind the theory.