I have a Dayton compressor motor that is missing the start capacitor. The motor runs good if I assist it to get started. The model # is 8YJ20B. It is single phase, 3450 rpm, 120v. I cannot locate what start capacitor to use on this motor. Can anyone help me out?

 

Best would be to email Dayton themselves.
From what I can find of 1HP Dayton motors that have 3450 rpm, they use a start capacitor of 519uF for 120V motors.

Different motor, but similar specs:
https://www.grainger.ca/ec/pdf/6K197_4.pdf

 

Yes, you should find that anything around from 450 to 500uf + should work, it is only in circuit for a couple of seconds.
Ensure you obtain a genuine start cap,,. regular electrolytics are no good for this application.

 

anything around from 450 to 500uf

??
Likely not that high. Around 70Mfd is common.

OP - does that motor have one or two caps on it (cap warts mounted on top)? It appears to have two, so my guess is, one start and one run cap.
https://offerup.com/item/detail/14c7ce01-793c-3ded-8c62-3a96dc69f790

 

I have a selection here that go up to 300uf !

 

??
Likely not that high. Around 70Mfd is common.

OP - does that motor have one or two caps on it (cap warts mounted on top)? It appears to have two, so my guess is, one start and one run cap.
https://offerup.com/item/detail/14c7ce01-793c-3ded-8c62-3a96dc69f790

The motor has 2 capacitors. The run capacitor came with the compressor. The start capacitor is missing. If I give the motor a slight assist, it runs through the cycle until the pressure switch shuts it down. When I attached a start capacitor to the motor it starts right up, runs for few seconds and blows the 20 amp breaker. It doesn't matter which of the 2 wires are connected, it responds the same. Is it possible that run capacitor is wired up to wrong leads?

 

Hello
Can you post how did you wire the start capacitor with that compressor?

 

There only 2 posts the red wire and the black wire. I tried both positions with the same result. You could hear the start capacitor click at the same time it threw the breaker.

 

The centrifugal start switch may be defective?
there is normally two windings, the higher resistance one is the start winding.

 

The centrifugal start switch may be defective?
there is normally two windings, the higher resistance one is the start winding.

I'm clueless to that. Sounds like pretty major problem. Is it not?

 

The start cap requires disconnection during the acceleration period of the motor, this is often done with a centrifugal switch mounted around the shaft, after years of use, it gets weak and often one of a few problems occur with it.

 

The start cap requires disconnection during the acceleration period of the motor, this is often done with a centrifugal switch mounted around the shaft, after years of use, it gets weak and often one of a few problems occur with it.

So maybe not such a big deal.