The compressor hums but will not start. The overload relay usually opens the common winding either internally or externally, this allows the windings to cool and not get hot enough to melt. This is very apparent when you place your hand on the compressor shell. It is very hot to the touch, and it would be difficult to keep your hand on the compressor.
■ Turn off the power to the compressor.
■ Remove all extra machine wiring attached to the compressor motor terminals.
■ Ring out the compressor and label the common, start, and run pins, (single phase)
■ Secure line one to the run pin and line two to the common pin.
■ Place insulated jumper wire from run to start, (see Fig. 3-13)
■ Turn on the power.
■ If the locked rotor breaks lose, the compressor will start and come up to speed in less than five seconds.
■ After compressor reaches full speed, remove jumper wire with compressor operating, leaving line one on the run pin and line two on the common pin.
To start a hermetic compressor motor which has a start capacitor, repeat the first four steps above. Step five is to place jumper wires between the run and start capacitors and from the start terminal to the start capacitor. It doesn’t make a difference on the hook-up of the jumper wires to the start capacitor terminals. See Tables 3-1 through 3-3 show operating current information. With your ammeter you can determine if a specific horsepower motor is operating properly. The tables are also helpful in sizing overloads and heaters for motor starters, especially when the data plate on the machine is missing or not legible. Never exceed the rated amperage of a motor. If you do, the motor will have a short life due to overheating the windings. Always remember that these ratings are given to be the maximum, when the unit has the maximum load on it, whether the motor drives a fan or a pump. All amperage ratings are given for the maximum. For instance, you are topping the charge of a reach-in freezer, or a walk-in freezer that is operating at the time of charging at five degrees below zero (-5 degrees F.), if you bring the compressor up to maximum amperage at this time, the unit will draw excessive amperage when terminating its defrost cycle and entering the freeze cycle. In fact, the compressor might trip its thermo-overload at that time.
