When troubleshooting a single-phase refrigeration compressor that will not start with the proper applied voltage, it’s important to determine the true cause. Too often, these compressors get replaced when they’re not really defective. Sometimes, an external component, such as a defective start relay, start capacitor, or overload, is the true cause. A technician must always check these components before condemning the compressor.

Misdiagnosing a compressor can lead to losing a customer and a poor business reputation. Since replacing a compressor is an expensive repair, some customers will get a second quote from another contractor. If the second contractor inspects the system and finds the problem to be a defective start relay, start capacitor, or overload, the initial contractor will look as if they’re trying to deceive the customer intentionally, when, in fact, they may have simply misdiagnosed the problem and prepared the quote based on that assumption.

Most times, when a non-defective compressor is replaced, the technician will never realize the mistake. New refrigeration compressors normally come with new starting components, so the problem gets resolved — but the true cause is missed. The technician will believe he diagnosed the problem correctly, when, in fact, he has not. So, again, it’s best to always inspect these external components before the compressor is replaced.

Ohmmeters or capacitance meters typically make it easy to determine if one of these external components is defective. However, there are times when a technician may question the condition of these components and lack full confidence if it’s the cause of the problem. Now, the technician is faced with not being truly sure of the defect and will most likely condemn the compressor.

There is a tool designed to assist technicians who face this situation. A compressor analyzer will allow a technician to start a single-phase compressor directly without using any of the system’s starting components. A compressor analyzer connects directly to the terminals of a compressor and uses its own components to start the compressor. This will allow a technician to determine if the fault is with the compressor or with the system’s starting components. If the compressor starts as a result of using the compressor analyzer, the problem is mostly likely an external component. If the compressor does not start using the compressor analyzer, the problem is most likely the compressor. This allows a technician to be more confident in condemning a compressor when he is not sure of the real problem.

Most compressor analyzers have other features that will further aid in diagnosing a defective compressor. Most can be used to test the integrity of the compressor’s windings by testing for an open or shorted winding. Most also allow the momentary reversal of the run and start winding to “bump” the compressor backward to attempt to break free a stuck rotor.

Replacing a compressor is never an easy or inexpensive task. Every effort should be made to ensure a compressor is truly defective before replacing it. When unsure of the true cause, using a compressor analyzer can make this process a little easier.

Publication date: 3/30/2015

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