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Substitute motor start capacitor


New Member
I'm working on a 120V window AC unit. I'm trying to add another fan motor. Since it drives both the condenser and evaporator fans, with a shaft coming out of both sides, I need to add another fan for the evaporator side. This is due to relocating the evaporator, evap fan inside my shop and leaving the noisy compressor along with condenser on top of my office in my shop.

It has a 6 uf dual start capacitor wired to the motor with a cap. Below is an image of the electrical diagram and the capacitor.

The cap is pretty expensive and don't really need a dual start capacitor, since i'll just be using for the 6 uF portion to power the fan motor.

My question to you is will any 6 uF motor start capacitor work or are they special? Does anyone know what a good substitute would be?

The fan motor draws 40 watts, 0.5 A @ 115 V

The capacitor states 55/6 uF 5.6/0.6A


Last edited:


Well-Known Member
Most Helpful Member
Yes, get a "film" capacitor or "polypropylene" capacitor with proper voltage rating or higher. Often called a motor "start capacitor" or motor "run capacitor" when you search.

Do not get a polarized (tantalum or aluminum electrolytic) for this AC application.


Well-Known Member
Most Helpful Member
These are convenient with the quick disconnect spade connector. And mounting lug. Link below...

Be careful, don't use a PCB Pin mount for a free-hanging application like you will be setting up. Also, the caps with wire leads on amazon do not have strain relief on the wires exiting the epoxy potting material. The lack of strain relief and motor vibrations will eventually break the wires at the epoxy line.



Well-Known Member
For one, I would not use motor start or run capacitors made in China, they are known to fail early.
The two types are motor start and motor run rated, the start capacitors I buy are usually made by CDE (Cornell Dubillier) and are oil filled paper.
The start capacitors are solid electrolytic bi-polar motor start rated, and are not marked by polarity and only meant to be in circuit for a very short period.

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