Hello,

I have a 1/4 hp rocking piston compressor that won't start unless I rock it side to side or give it a little bump. It only takes one little bump and it starts every time but it won't start without it no matter how long I wait. When I give it power it just hums softly. Just curious if anyone has ran across this or has any ideas on how to fix it the pump. It is less than one years old. Thanks!

I bet Tony (sprkplug) knows how to fix this. Give him a private message if he doesn't see this soon.

Does it utilize a start capacitor?

Yes, it is clipped to the side.

The cap is a possible culprit, if the compressor turns free by hand with no binding whatsoever. You can check the cap if you have a meter with capacitance function, or swap it out for one known to be good.

Thanks! I checked the capacitor (didn't know what it was for), is labeled 30uF and I am getting a reading of 150 uF. I will order a new one and try that. Will let you know if it fixes the problem. Thanks again!

Most of the time the start cap will be leaking goo if they are bad or gone. Most all I have replaced do.

That is a weird reading. A 30 micro Farad capacitor would normally loose capacitance if it has failed. To gain capacitance............... don't know about that one.

Could there be another zero on that 30 that has faded out where it is hard to read?

I too bet that is it as well. They will also normally "swell" up when they go bad. The ends might be bulged out.
Cheap once can be had around here at an HVAC parts house.
Dave C

Don't smell them if you touch the end with your nose and the cap discharges you will know it.

Dono...And you know this how??

Thanks all, it was the capacitor at fault. Replaced it and it's working good. Thanks again for the helpful advice!