Substitute motor start capacitor?

Thread Starter


Joined Jun 9, 2010
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 on backorder and don't really need a dual start capacitor, since i'll just be using it 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 where I can find a cap that will work?

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

The capacitor states 55/6 uF 5.6/0.6A



Joined Jul 18, 2013
As posted on the other site.
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.


Joined Jan 23, 2018
If you are using a separate motor then you will need to use whatever value is specified for that separate motor. In addition, the capacitor for the fan motor in a window unit is a run capacitor, rather than a start capacitor. No start switch or relay.