HVACPROTECH® TECHNICAL ARCHIVES
Checking a Run Capacitor Under Load
First you measure the Start winding current.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Then you measure the Run winding & Common winding together.
You are measuring differential current here.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The two readings should be within a few 1/10ths of an amp of each other if the capacitor is not weak.

Then I check it with no wires attached under no load.
That is a 28.44 mfd reading on a 30 mfd run capacitor. This is well within the +/- 10% rating that was on the capacitor