Evaporator motor checkout
Per. the South Jersey Appliance data sheet, you can go to the motherboard in the back and measure both resistance and voltage and frequency at the J2 connector. This schematic is generic so refer to the fridg's schematic to confirm wiring and double check with wire colors at the evaporator motor.
J2 pin 3 to J2 pin 4 about 12.3 vdc @ high speed,8 vdc at medium speed,4vdc at low speed. J2 pin 3 to J2 pin 1, 220 hz high speed, 160 hz medium speed, 100hz low speed. I would assume opening the fridg door would give a high speed signal. Resistance should be about 2K. I believe the signal is a square wave with a dc component. A analog meter will not give the same readings. A digital meter reads RMS value, analog an average.
For units with the annoying fan noises, changing frequencies/voltages will confirm a bad motherboard.
This evaporator motor is more complex than any other and it is recommended to replace whenever the motherboard voltages fail. Simple resistance checks of the motor are probably not useful. Usually a zero volts output cause is a blown resistor near the J2 connector.
Burned apart one of these evaporator motors today. This particular motor had bad bearings from water damage. It is a simple 6 pole, symetrical induction motor with a slight shading to force it to start in the right direction. This shading comes from one set of wires, the other must be a variable duty cycle square wave as this motor is not a permanent magnet dc motor.The variable duty cycle square wave provides different controlled power pulses that effectively vary the speed just like a domestic fan motor speed control device. The starting torque is probably low and frictional looses from the bad bearings probably stalled the motor and the excess current draw blew the motherboard. It is a good idea to place a slinger on the motor shaft below the fan blade to prevent this type of failure.
For the South Jersey schematic crunch in Google" junk GE GSS20IEMbww new motherboard" Make sure to enter it exactly as shown with the same capital letters.
Also, you can remove the three pin connector for the compressor/defrost power and jumper the ( these pins are identified on the motherboard)power input pin J11 to either the compressor J9 or the defrost circuit J8 to activate independent of the motherboard. Generally, if the heater draws current as measured at the jumper, the heater and defrost thermostat are ok,and the motherboard is bad.
With this schematic, you can measure all the thermistor resistances and input/ output voltages.
Also, I just realized this board contains the auger motor and auger solenoid drivers and the water dispenser solenoid. So, if these fail, it's the motherboard. The triac drivers for the condenser motor and the evaporator motor are rather small and rated less than 1/2 amp so they blow real easy whenever these motors go bad.
Also, I found out the dispenser water solenoid and auger drivers are small relays on this board, but the encoder signal inputs are never defined anywhere!
UPDATE 7-18-09 South Jersey schematic no longer available, Refer to fridg schematic, sorry, out of my control.
Last edited by richappy : 05-18-2012 at 04:32 AM.
Reason: Add evaporator motor details