Tip & How-To about Heating & Cooling

Hard Start Capacitor A hard start capacitor, its only purpose is to add additional starting torque when the compressor is starting and for just a few milliseconds. It is wired thru a normally closed set of points in a potential relay and in parallel with the run capacitor, when the compressor is starting the start capacitor is in the circuit adding additional starting torque to the compressor, when the compressor reaches a certain speed it generates enough back EMF (voltage) to energize the potential relay coil and open the normally closed set of points and take the start capacitor out of the circuit and then will stay open, keeping the start capacitor out of the circuit as long as the compressor is running. The hard start capacitor is only in the circuit or working for a few milliseconds, it?s not doing anything once the compressor s back EMF opens the potential relay coil. These potential relays have different cut in and cut out voltages, so the same relay won?t work with any compressor and may actually damage the compressor or shorten its life if you don't use the right potential relay. The compressor manufacturer and the local parts store list the correct capacitor start relay and start capacitor for every compressor and now they are putting the information on the compressor on the nameplate with the model and serial number. As a rule of thumb you can use a capacitor or start capacitor within 10% of its rating if you can?t get the correct one.

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I have a 38ckc036750 A/C Unit and the fan run when the contactor closes but the compressor dont, the is a hard start capacitor that is across the run capacitor. what must I do to get the compressor going. thanks


many technicians make the mistake of using a hard start kit instead of replacing a bad run capacitor, the problem is that it can be ******* the compressor, and the start capacitor can also go bad, you can start with removing the capacitors and replacing with a new run capacitor and see if that gets it running, also can try another start capacitor with the new run capacitor, some manufactures engineer there systems in that way, if not the compressor may be done. *Be sure to check all the electrical connections including those at the compressor under the terminal cover.

Aug 22, 2011 | Carrier 38CKC036 Air Conditioner

1 Answer

Hard Start Capacitor A hard start capacitor, its only purpose is to add additional starting torque when the compressor is starting and for just a few milliseconds. It is wired thru a normally closed set of points in a potential relay and in parallel with the run capacitor, when the compressor is starting the start capacitor is in the circuit adding additional starting torque to the compressor, when the compressor reaches a certain speed it generates enough back EMF (voltage) to energize the potential relay coil and open the normally closed set of points and take the start capacitor out of the circuit and then will stay open, keeping the capacitor out of the circuit as long as the compressor is running. The hard start capacitor is only in the circuit or working for a few milliseconds, it?s not doing anything once the compressor s back EMF opens the potential relay coil. These potential relays have different cut in and cut out voltages, so the same relay won?t work with any compressor and may actually damage the compressor or shorten its life if you don?t use the right potential relay. The compressor manufacturer and the local parts store list the correct capacitor, start relay and start capacitor for every compressor and now they are putting the information on the compressor on the nameplate with the model and serial number. As a rule of thumb you can use a capacitor or start capacitor within 10% of its rating if you can?t get the correct one.

Feb 17, 2010 | Heating & Cooling

1 Answer

when it starts to work there is no problem until it reach the desire temp. the comprossor stop & not starts again even the temp of the room raise up


It sounds like your unit has a bad start capacitor or start relay. If you have a thermostatic expansion valve a lot of times the unit pressures won't equalize for long periods of time, so the compressor needs additional starting torque. If you let the unit set long enough the pressures will equalize and the compressor will start, but if you try to restart it before it equalizes then the start capacitor and start relay add the additional starting torque, to allow the compressor to start with unequal pressures.
You probably already have them and they are bad, if not you need to have them added to your system.

May 31, 2010 | Mitsubishi Mr. Slim MXZ30TN Air...

2 Answers

new copeland compressor wont start


Hello,By all means install a hard start kit on the cap.Your wiring is correct.A scroll compressor usally doesn't need a start kit but I have seen 5 ton units that take one.Check the compressor tag and make sure the compressor is not a 3 phase motor!

Apr 21, 2010 | Heating & Cooling

2 Answers

Hard Starting Dometic Rooftop AC unit


Just add a$10:00 hard start kit to the compressor.

Sep 06, 2008 | Dometic Rooftop RV Air Conditioner

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