Swollen capacitor

Question: What would cause a capacitor to bulge and is it something that can be avoided?

-John West, Chester, Va.

Answer: The bulging or swelling that can happen to a run capacitor, whether it be for a compressor or fan motor, is caused by overheating due to an over current condition. Could it be avoided? Maybe.

The first thing to determine is what could cause an over current condition at the compressor or motor. Moore than likely it was an overload of come sort. One example is compressor short cycling, which is the condenser being turned off and immediately back on. This could cause the compressor to pull higher-than normal- amps.

A compressor needs enough off time, five minutes or so, for the system pressures to equalize. If the system is one that pressures don't equalize in the off cycle, then hard-start components need to be installed.

That would be the next thing to check: Does the system have or need hard-start components? All single-phase air conditioners would benefit from hard-start components, which increase the voltage temporarily during startup. This makes it easier for the compressor to start. If the system has hard-start components and they are faulty, the compressor will pull high amps on startup, maybe even locked-rotor amps. That could lead to capacitor problems.

Another possibility for over current problems could be a dirty condenser, which would lead to higher-than-normal head pressure and to higher compressor current draw.

If a faulty run capacitor is found, you should replace the faulty capacitor with a new one with the same microfarad rating and the same voltage or higher. Then get the system running and check the current draw at the compressor during startup and again after the system has been running for 10 to 15 minutes.

If it was a fan run capacitor that failed, then amp out the fan motor once it starts. If the current draw falls within manufacturers specs found on the system data plate, then the old capacitor probably just gave it up. Sometimes it is just a faulty capacitor.

-Scott McClure, CM, hvacr contractor and instructor. Reference “Refrigeration and Air Conditioning Technology,” Whitman, Johnson, Tomczyk. 5 th edition, page 377