Images of motor Start capacitor blown up


Picture of motor hard start capacitor with top blown off.
Top view of compressor motor starting capacitor that blew its top off. This device is used in what is called a "hard start kit". Every single phase air conditioning or refrigeration compressor should have one. These devices are also used on high torque applications like air compressors and pumps. If your system is tripping the circuit breaker on a regular basis this repair should fix the problem. Please do not install a larger breaker or fuse to stop nuisance trips. If you have fuses in your outdoor disconnect and they are causing you problems with blowing. I recommend replacing them with copper tubing and installing the correct size circuit breaker (a 3 ton system can get away with a 20 amp breaker and 2 ton  15).


Motor start capacitor next to run capacitor in control box. For groundsource heat pump and pool heater.
    Image of Starting capacitor in control box behind motor run capacitor. This control box is used on a system that is a combination groundsource heat pump and swimming pool heater.

Notice the wires in the top right corner of the service cabinet. This box also has a 2 pole Honeywell contactor and Idec low voltage control relays. The relay in the center of the box is a GE MARS 165 potential relay that controls the starting function (a ge mars 66 and a 150MFD 330volt cap. will do most systems). It was ok untill recently even though this system stops and starts a lot, being on continuous pump down. I finally had to replace the relay and used a univeral electronic relay which I don't like, the mechanical relay worked so much better.

Any refrigeration system that uses a TEV (thermostatic expansion valve) instead of a capillary tube or orifice must have a start capacitor because the system pressure may not equalize for a period of time during the off cycle.

    If you replace the indoor cooling coil with one that has a thermostatic expansion valve you may think that there is a problem with the compressor if it doesn't have one. A shorted start capacitor can cause the system to trip the circuit breaker.

Most of the so-called "solid state" start assist devices are garbage because they use thermistors instead of a relay, don't even bother to install them. Use a start relay and start capacitor like shown above. There are some two wire start assist devices that really do work such as "Kick Start" but they must connect the start capacitor directly to the circuit.

    Ge/Trane/Manurope compressors generally don't need a hard start kit but it will still help. Most scroll compressors have no need for a start kit but they do need a anti-restart timer or they can run backwards.


Start assist devices:

  1. Just the run capacitor, will work with no pressure differential and used or Scroll compressor. (ok).

  2. Add a thermistor across the run capacitor. (Better than nothing). Used on Carrier and other brands.

  3. Install a thermistor in series with a start capacitor (Better than #2 but not even close to #4). Most of your cheap start assist devices are configured this way and help a lot but will substitute for the real  thing.

  4. The real thing. Like described above a potential relay and start capacitor will do wonders for a compressor that won't start properly. Most contractors will try to sell you #3 and swear it is a "start kit". B.S.



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