Service Repair

Mastering Diagnostics #22: Introduction to the Internal Heat Exchanger (IHX)

March 25, 2025

A/C systems have become notably smaller but still have to perform. Reducing the carbon footprint is the goal with R1234yf, but the IHX optimizes the performance of the refrigerant

Brandon Steckler

Welcome back to Mastering Diagnostics! This is episode #22 and Brandon takes us through the operation of the internal heat exchanger (also known as an IHX). With the carbon footprint stringencies and emissions standards in place, it’s no surprise that the demand for more energy efficient and less harmful A/C systems are in.

The implementation of R1234yf has been necessary to achieve these standard but the new refrigerant does not cool as efficiently as its predecessors (R12 and R134a). This is where the IHX comes to be an important part of the equation to boost efficiency.

Serving as a Siamese refrigerant pipe, the IHX incorporates both the high-side liquid line and the low-side suction hose in one assembly. The difference in sensible heat between these two distinct portions of the IHX gives it its magic.

Sensible heat from the high-side is transferred (through conduction) to the low-side. As a result, the high side/already liquified refrigerant is sub-cooled. That is, the temperature of the liquid refrigerant is further lowered, giving it more heat-absorbing capacity when it passes through the evaporator. This increases the efficiency of the system.

At the same time, the transfer of heat (from the high-side to the low-side) causes the vaporized refrigerant of the low-side to super-heat. That is, the gaseous refrigerant takes on additional sensible heat. As a result, the super-heated refrigerant is sure to remain in a gaseous state as it returns to the compressor. This ensures, even with a fully throttled expansion valve (high rate of refrigerant flow), that the compressor is unlikely to slug with liquid refrigerant.

The IHX has been in place for many years, but many technicians are still mystified by its operation, even with no moving parts. Although its rate of failure is almost non-existent, knowledge of its functionality is important to the modern-day A/C diagnostician.

Stick with Brandon as he demonstrates thermodynamically how a refrigerant loop carries out its goal of efficient heat transfer. Thermal energy transfer can actually be visualized when implementing an engineering tool known as an enthalpy chart. Watch as Brandon leverages the power of an enthalpy chart to plot data from both a properly functioning and malfunctioning refrigerant loop and also a vehicle experiencing a poor-cooling symptom, but the fault has nothing to do with the refrigerant loop. All this can be easily derived from the enthalpy chart. And all you have to do is tune into this episode of Mastering Diagnostics!

There's lots more from Motor Age! Check out our Motor Age video library

Receive your FREE SUBSCRIPTION to Motor Age!

Each issue is packed with in-depth technical articles from experts, brief tech tips and repair strategies, TSBs, and much, much more!

DID YOU KNOW? Motor Age offers a library of ASE Certification training materials. Motor Age Training's books, practice tests and video resources are edited by ASE Master Technicians with years of experience in repair processes. Each product is designed to help you prepare for and pass your ASE certification exam – GUARANTEED. CLICK HERE TO FIND OUT MORE:

FOLLOW US ON FACEBOOK

VISIT OUR WEBSITE FOR EVERYTHING AUTOMOTIVE

@@@@@@@@@@@@@@@@@

Due to factors beyond the control of Endeavor Business Media, it cannot guarantee against unauthorized modifications of this information or improper use of this information. Endeavor Business Media assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Endeavor Business Media recommends safe practices when working with power tools, automotive lifts, lifting tools, jack stands, electrical equipment, blunt instruments, chemicals, lubricants, or any other tools or equipment seen or implied in this video. Due to factors beyond the control of Endeavor Business Media, no information contained in this video shall create any express or implied warranty or guarantee of any particular result. Any injury, damage, or loss that may result from improper use of these tools, equipment, or the information contained in this video is the sole responsibility of the user and not Endeavor Business Media.

The tool and/or equipment featured in this video was supplied by the manufacturer and may or may not be retained by the reviewer at no cost.

About the Author

Brandon Steckler | Technical Editor | Motor Age

Brandon began his career in Northampton County Community College in Bethlehem, Pennsylvania, where he was a student of GM’s Automotive Service Educational program. In 2001, he graduated top of his class and earned the GM Leadership award for his efforts. He later began working as a technician at a Saturn dealership in Reading, Pennsylvania, where he quickly attained Master Technician status. He later transitioned to working with Hondas, where he aggressively worked to attain another Master Technician status.

Always having a passion for a full understanding of system/component functionality, he rapidly earned a reputation for deciphering strange failures at an efficient pace and became known as an information specialist among the staff and peers at the dealership. In search of new challenges, he transitioned away from the dealership and to the independent world, where he specialized in diagnostics and driveability.

Today, he is an instructor with both Carquest Technical Institute and Worldpac Training Institute. Along with beta testing for Automotive Test Solutions, he develops curriculum/submits case studies for educational purposes. Through Steckler Automotive Technical Services, LLC., Brandon also provides telephone and live technical support, as well as private training, for technicians all across the world.

Brandon holds ASE certifications A1-A9 as well as C1 (Service Consultant). He is certified as an Advanced Level Specialist in L1 (Advanced Engine Performance), L2 (Advanced Diesel Engine Performance), L3 (Hybrid/EV Specialist), L4 (ADAS) and xEV-Level 2 (Technician electrical safety).

He contributes weekly to Facebook automotive chat groups, has authored several books and classes, and truly enjoys traveling across the globe to help other technicians attain a level of understanding that will serve them well throughout their careers.