What size AC capacitor do I need?

What size AC capacitor do I need? Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner’s manual. The resulting number is the MicroFarad of the capacitor you need.

What happens if you use the wrong size capacitor? This is why oversizing a capacitor can quickly cause damage to a compressor. By increasing the current on the start winding the compressor start winding will be much more prone to early failure.

Is it better to use a bigger or smaller capacitor? All capacitors are not equal in their performance. Using a bigger cap is not always the best answer. Ideally, the capacitor should be sized for the amount of charge needed to supply transient current to the circuit for which the capacitor is filtering or decoupling.

Can I use any capacitor for my AC unit? No. Start capacitors and run capacitors have too many differences to be interchangeable. Using a start capacitor in place of a run capacitor would short out your AC system and would likely lead to the fan motor and/or compressor malfunctioning.

What size AC capacitor do I need? – Additional Questions

Can I use a 7.5 capacitor in place of a 5?

It will not make it ‘run better’. If anything, it will run less efficiently but the difference will likely be negligible.

Can I replace a capacitor with a higher UF?

You can almost always replace a capacitor with one of a higher voltage. This is the limiting factor of a capacitor due to dielectric breakdown voltages that the manufacturer chose.

Are AC capacitors universal?

Ultimately, capacitors are universal parts, so shape, size, brand, and other basic factors aren’t exactly important — just remember to get the appropriate voltage and microfarad and you’ll be set.

Are all AC capacitors the same?

Your air conditioner may actually contain several different capacitors, including the compressor motor run capacitor, the outside fan motor run capacitor, the indoor fan motor run capacitor and the start capacitor. The most common capacitor to fail is the compressor motor run capacitor.

How do I know which capacitor to use?

The capacitor physical size is directly proportional to the voltage rating in most cases. For instance, in the sample circuit above, the maximum level of the voltage across the capacitor is the peak level of the 120Vrms that is around 170V (1.41 X 120V). So, the capacitor voltage rating should be 226.67V (170/0.75).

How do you match an AC capacitor?

Does a capacitor have to match exactly?

The rule for replacing capacitors in regards to voltage is always to be equal or greater, but never lower.

Does physical size of capacitor matter?

Generally no, the physical size of an electrolytic capacitor is not a factor as long as the capacitance and voltage ratings are the same. A possible exception is, if it’s a switching power supply that uses low ESR capacitors, then the sizes might be different.

How often should you replace AC capacitor?

In general, you can expect most AC capacitors to last about 20 years. This is a fairly long lifespan, which is why most heating and AC repair companies will take a look at the capacitor last.

What happens if you put the wrong capacitor in an AC unit?

A wrong capacitor rating or a poor quality capacitor causes an inefficient motor, which causes an under-performing system, which eventually results in either a stopped system, or at the very least, a reduction in the airflow and comfort to the homeowner.

Can I replace my own AC capacitor?

Answer: Yes and yes. It could be a capacitor, or it could be the compressor. Since capacitors are cheap it may be worth a try to see for yourself if that’s it, if not you will need a technician. There is really no “DIY” fix when it comes to repairing or replacing a capacitor.


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