Warning:The purpose of this article is to inform the customer that if the evaporator motor fails to run, the motherboard is replaced, and the evaporator motor is not replaced/repaired, the evaporator motor will burn out the new motherboard virtually 100% of the time!
Background:
The motor is a six pole induction motor, with copper windings. Sometimes the motor will ingest water and the increased friction, due to bad beaqrings, will load down the motherboard driver and burn it out.The more common problem is the motor just running out of oil. There is a resistor near the j2 connector that will burn open.This is a high efficiency motor with a small air gap between rotor and stator. It is not an impedance protected motor and it is possible, under certain conditions, the motherboard will not safely limit current in a power controlled stall condition,and the motor will draw excessive current and burn out the motherboard driver.This condition is rather rare.
The motherboard will send out a dc voltage from J2 connector pins 3 and 4 and probably a square wave from pins J2-3 and J2-1. The square wave will vary in frequency to speed up, or slow down the motor.
If one of these voltages are missing, or both are near the 12.3 volt limit, the board is not putting out a square wave and the motor will not run, but just draw excessive current which burns out the motherboard, but usually not the motor widings.
Just recently disected some failed evaporator motors ( the 115 volt,open frame type) and found they either had insufficient oil or the wrong type, it must be turbine type oil that will not gum up from the low freezer temperatures.Part #55191, but I would not add this oil to the GE motors.
The GE motors may have the same problem.
Conclusion:
Most failures are initiated by a motor failure which burns out the motherboard.To confirm, turn the motor while holding the housing, if you feal any roughness, the bearings are bad.If the bearings are good, the motherboard may have failed in some way. In this case, I would still repace board and motor as there is no way to reliably confirm which item is bad and which item initiated the failure. It is also possible the motor windings are burnt if the motherboard put out a dc level only, but I have never seen this happen. Generally, replacing the motherboard only, will result in board failure.
Fortunately, all emperical evidence points to a "fail safe" motherboard driver. When the evaporator motor fails and draws high current, the driver in the board will fail permanently and a replacement of the evaporator motor only will not result in motor failure!
Also, many persons lack the skill to use a meter,thus it is advised to allways replace both the evaporator motor and motherboard at the same time. It is suggested that Appliancepartspros provide these as a kit at some reduced price, if possible.
In the future, I will confirm the above with my portable scope.
Any comments are wellcome.
Update #1
Removed the bottom endbell from a failed motor. Found the motor to have permanent magnets defining it as a brushless dc motor with the external square wave providing comutation. Suspect the application of only dc voltage will allow the motor to run, but with limited starting toque and the motor might not run in the right direction as the square wave provides starting torqe to force it in the right direction.
Motor ran out of oil and the high rpm friction drove the current sufficiently higher than normal resulting in motherboard driver failure.
Suspect the motor windings are ok and addition of oil in both enbells would reduce friction and not burn out the motherboard.Therefore, it is sugested that addition of zoomspout oil (part # 55191 available at Lowes) to both upper and lower bushings after several years of use, should prolong the life of the motor. This is facilitated by prying off the bottom enbell and pulling out the armature. The addition of oil must be carefully added to prevent oil saturation of the armature that will prevent the motor from starting as it is a low starting toque motor. Suspect most of the friction was from the lower enbell thrust washer, so it is suggested to add more oil to the bottom enbell felt pad.
Unfortunately,at this time, there is no test proceedure for a re-oiled motor and the customer is advised not to assume it is ok.
In the future, when I get a fridg to work on, I will confirm the statements above.
Update:
The new motherboards WR55X10942 have relays that replaced the transistor drivers so I suspect these boards will not fail when the evaporator motor fails as the relay can provide all kinds of excess current. The only limit is the dc supply which could burn out if there is a short.
Would be nice if a GE tech could confirm this.
Latest update;
I believe the square wave is just a choped up dc level. To properly measure the square wave from pins J2-1, and J23, and between J2-3 and J2- 4, use a 300 mf capacitor in series with a meter set on ac mode to prevent false readings. A presence of voltage will proove the motherboard is putting out a square wave.
