View Full Version : Compressor capacitors

14-05-2014, 06:39 PM

Got a theory question.

Wanting to understand how to wire up run and start capacitors a bit better.

Example: single phase motor

Would I connect the run capacitor in parallel with the run winding and same goes for the start capacitor with the start winding?

Website links or good explanation would be great,


14-05-2014, 07:04 PM
I would check out the wiring diagram you got with the compressor . Unless you have decided to fit extra capacitors?

The capacitor is normally wired in parallel with the winding often using the potential relay as a juction box.

www.novakool.com/.../R134a_12-24V_DC_11-01_ or Re: Compressor Starting Equipment and Wiring Diagram ...
www.youtube.com/watch?v=cuMHBUFXxFcPrevedi ovu stranicu
21. ožu 2009. - Re: Compressor Starting Equipment and Wiring Diagram ... Playing with a V Twin Danfoss Compressor and Inverter VFD by Aussie50 22,887 views; Thumbnail ... How to check the windings of a refrigeration compressor by ...

14-05-2014, 07:27 PM
Thanks for the fast reply, I don't have a manual. It for an NVQ I'm doing, gonna need to be able to draw a wire diagram for a single phase compressor. I'll check out the link you posted.

14-05-2014, 09:03 PM
Looked into it more. Am I right in thinking once the starting capacitor has done its job and been switched out of the circuit, that the starting winding is still used for normal running and that is why there is a running capacitor.

So both windings are in use during running of the motor.

monkey spanners
14-05-2014, 09:53 PM
Yes both windings are used to run the motor, the run capacitor is permanently connected to the start winding, while the start capacitor is switch out of circuit once the motor has started. This is for CSR motors (capacitor start and run)
A PSC motor just has a run capacitor, it is low starting torque and more common in use as a fan motor though some older air con systems use them.
A CSIR motor is more common in small commercial fridges and freezers, they only have a start capacitor which is switched out of circuit once the motor is started, they continue to run only on the run winding.

15-05-2014, 09:03 PM
Ok I've got it! What I was trying to get is:

The capacitors are wired in series with the start windings but the capacitors are in parallel with one another.


monkey spanners
15-05-2014, 09:14 PM
Yes they are in parallel so that their capacitance adds up. So a 100uf start cap and 15uf run cap provide 115uf of starting capacitance.

15-05-2014, 10:33 PM
Yea and the start cap is switched when it gets up to speed, thank you for the responses