Re: Frigikar air conditioning in my Packard

Posted by Troy Taylor On 2014/5/20 10:04:59

You must be able to freely move the motor shaft (rotor) to thoroughly conduct the motor tests.

Attach the alligator clip leads to each of the motor power input wires.

Turn on the volt ohmmeter and switch it to the "Ohms" setting. Touch the lead ends together and the meter should read a direct short or zero ohms.

Attach the other end of the alligator clips to the leads of the volt ohmmeter. You should receive an immediate reading in ohms of approximately 10 to 100 ohms on the meter. This wide range takes into account for the carbon brush connection to the rotor windings.

Rotate the motor shaft very slowly in either direction. The ohm reading on the meter should change as you rotate the shaft. This insures that the carbon brushes are making contact through the commutation plate of the rotor.

Remove one of the alligator clips from the power wires and touch it to the motor frame. You must find a metal part on the motor case to see if the motor has a short to ground. If the meter registers a wide-open or infinite ohms the motor does not have a direct short to ground.

Rotate the motor shaft again. Again the meter reading should be infinite ohms or a wide open. If this is the case the motor is fine and perhaps the power source is the problem. Check the power wiring for any short conditions. If the motor does indicate a short or zero ohms you must remove the end case cover that conceals the motor commutation plate and carbon brushes.

Remove the end plate with the screwdriver. The long screws can be either a Philips or slotted head screw. The two screws will go through the case and into the shaft end of the motor case. Remove the screws completely from the motor.

Pull the end cover off carefully and inspect the wiring that feeds the carbon brushes. The bare copper braid wire may have touched the case. If it has, carefully pry the braid wire from the case and retest the motor for a short.

Pull the rotor from the stator portion of the motor, if the ohm test still registers a zero ohm or short reading between the windings and the motor frame.

Inspect the condition of the rotor windings. Chances are the windings maybe scorched from over heating or the protective varnish has been damaged. This will cause the DC motor to be shorted to the case from conduction through the shaft into the bearings and then the outside case. If the windings are damaged in any way, the motor will have to be rewound.