Troubleshooting a Capacitor


What is a capacitor? What does it do for your air conditioning system you might ask. Well, let me tell you. A start capacitor is the silver cylinder pictured in the control panel of this air conditioning condenser above. Its function is to start your compressor and your condenser fan motor. Basically a capacitor stores an electrical charge and consists of one or more pairs of conductors separate by an insulator. Its used on all single phase 240 volt, and 120 volt applications in residential HVAC systems. The amount of electrical storage capacity on a capacitor is known as capacitance. This is what every capacitor has printed on the side of it. Usually that rating is given in microfarads. A capacitor with a dual rating, like the ones used in many outdoor air conditioning units, is used to start both your compressor and fan motor. One side of that capacitor can go bad without affecting the other side. Then again, sometimes both can be bad. They’re easy to test using the MFD setting on a multimeter used by many technicians, by putting one lead on the common terminal and the other on either hermetic, or fan terminals. The reading should give you the rating of the capacitor +/- a few microfarads. If its greater than 5 microfarads off from the rating, you should consider changing, or calling a professional to consult on the best course of action. When a Capacitor “blows” we often consider that a symptom of a greater problem, than we do the source. They are the weakest link in the electrical chain often times. A bad compressor motor, or windings may be the root cause. Other factors, like the unit running low on freon (addressed in another post) can also drain a capacitor. Sometimes the solution is simple and it only involves changing the capacitor, until the next record breaking hot day comes. Sometimes however, the problem can be multi-faceted and require listing the aid of a professional with experience to look at all aspects of your central heating and air system performance and evaluate whether other areas need correction. If you’re uncertain as to what is happening with your own HVAC system, and want someone who can break the problem down into bite sized pieces without throwing a bunch of trade or tech jargon at you, contact the helpful professionals at Top Gun Air for a better understanding of how your system works, and maintenance practices that can help you avoid costly repairs.
Best practices by our technicians never include placing flammable cardboard packaging the capacitor comes with IN your A/C system. Like the one pictured that we pulled off a package unit on a commercial building in downtown Dallas. The owner spent over and hour splicing wires that the insulation got burned off of inside the unit. If you ever see a technician working on your unit doing this, stop them and tell them to mount it properly.

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