Walk-in refrigeration parts, one at a time
By Vimal Bhaya, Founder and Lead Systems Architect · Last reviewed 4 October 2026
Every troubleshooting answer for a walk-in ends at a part: a coil, a valve, a fan, a timer. These pages take one part at a time, so you know what the technician means when they name it, and what that part looks like when it fails.
This guide is growing. It starts with the two parts on the cold side of the system: the evaporator coil, which pulls the heat out of the box, and the expansion valve, which decides how much refrigerant reaches it. More parts will follow.
The 2 parts, in order
By the end you will know what normal frost on a coil looks like and what each ice pattern points to, why coils leak and what to check from the floor, the three kinds of expansion valve and how to tell which one you have, and why a technician needs two readings to tell a blocked valve from a refrigerant leak.
-
1. The evaporator coil
The cold radiator under the ceiling. Light frost that clears at every defrost is normal. Ice that stays is a fault, and where it sits points to the cause. Plus why coils leak, and five checks you can do from the floor.
Read part 1 -
2. The expansion valve
The part that decides how much refrigerant reaches the coil. Capillary tube, TXV or electronic: how each one works, which one you probably have, and how a fault in each shows up in the box.
Read part 2
How to use this
Read them in order if you are starting from scratch. That is the usual path. If you already know which piece you need, jump to it from the list above.
Each part page links to the symptoms that part causes, on the pages of how walk-ins work, and how they fail. So you can go from a symptom to a part, and back again.