Call toll free 1-866-584-0355 or 1-903-759-2160 or fax 903 759 4605
309 Patriot Circle, Longview, TX 75604-2240

THINGS TO CHECK IF THE COMPRESSOR HUMS BUT WILL NOT START:

• Run capacitor.

  Look for the larger run capacitor for the compressor (or it may be like this picture and housed in the same body with the fan motor run capacitor). Examine it for bulging or bad wiring terminals or wires. Make sure no fluids have escaped or there are no ruptures. If you cannot check its capacitance and you suspect it has a problem, take it to a service shop or supplier and let them test it.

• Compressor terminal wires. Open the compressor TERMINAL BOX COVER on the side of the compressor and examine the wires and terminals for defects.
• Contactor and points. Make very sure all the connections for the compressor wire are good and that there is no break of the wires in route to the compressor. Examine the points of the contactor.
• Start capacitor and relay. Look for physical damage to the capacitor and have it and the relay tested or replaced if necessary or if you are in doubt.
• High voltage. If you have a three phase voltage to the unit, make sure all the legs of the supply current are proper voltage.
• Stuck compressor. If the internal bearings are bad or if the oil inside the compressor has all migrated out into the system or if air has been allowed into the system, then the compressor can stick. This means that it is frozen in that one position. If you can get it to move just a little bit, you might can save it for a while. It will be damaged to the point of needing to be replaced, but you might can get cooling for a while if it will come unstuck. Read the material in Compressor will not start but the outdoor fan runs.

• Human error. Make sure you are not just hearing the hum of the contactor instead of the hum of a compressor that won't start.
• External overloads. On some older units and many of the big units, the compressor has external overloads in the wires going back to the contactor from the compressor. These overloads can and do become weak and may need replacement. It can be and should be checked -- especially if it is a three phase unit.

¹ Brand names, product names or trademarks listed belong to their respective holdings.

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If you have comments or suggestions, please email me at James' A/C Co.

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