The importance of understanding and using wiring diagrams to troubleshoot refrigeration systems cannot be overemphasized.

Most system problems can be divided into two broad categories: electrical or mechanical. However, the majority of system problems are electrical. Mastering the use of wiring diagrams enables a technician to better troubleshoot the system electrically, which will facilitate troubleshooting the entire system with more accuracy and precision.

A typical wiring diagram shows the actual point-to-point connections of all the system components, including the color of the interconnecting wiring. Each of the components is represented using generally accepted universal symbols.

Besides the popular wiring diagrams, there are several other types a technician may encounter. These include the pictorial diagram, which also shows the point-to-point connections of the components, but the components are drawn to look more like the actual components.

The schematic diagram is similar to a wiring diagram, except it does not show the actual point-to-point connections of the components.

A ladder diagram is a simplified version of the schematic diagram and is much easier to follow.

Many manufacturers include two types of diagrams with their equipment, most commonly a wiring diagram and a ladder diagram.


Wiring diagrams can aid a technician in many ways. They allow a technician to systematically troubleshoot a problem. By analyzing the system’s wiring diagram, a technician can see where the common junction is located that could affect the components that aren’t working.

The technician can then start at that point without having to check the entire system. For example, a technician arrives on the job and finds that the compressor is the only component of the system that is not running. By studying the wiring diagram, it can be quickly determined from where power is applied to the compressor and which components are wired in series with it.

When possible, it is a good practice for a technician to keep on hand wiring diagrams of the equipment most frequently serviced. Most equipment will have a wiring diagram on it. However, many times these diagrams are worn and hard to read. Keeping a good copy on file will ensure that the information will be readily available when needed.

If a wiring diagram is not affixed to the cabinet of newly installed equipment, it is a good idea to leave a copy of the wiring diagram from the instruction manual with the equipment.

On built-up systems, it is a good practice to make a wiring diagram and leave it with the equipment so the next technician on the job can refer to it.

When making any wiring changes or adding/subtracting any component, remember to mark these changes directly on the wiring diagram. This will allow the next technician on the job to quickly see the modifications.

Understanding and using wiring diagrams properly is an essential part of correctly serving any refrigeration equipment. A technician should master their use. This may require some practice and patience, but it will pay off in the end.

Marchese is owner of Coldtronics, Pittsburgh, PA. He can be reached at 412-734-4433; (website); or (e-mail).

Publication date: 05/06/2002