Our 1987 Whirlpool Imperial has served us well until a recent issue with a too-warm freezer. With all other systems apparently OK after inspection, I removed the back panel of the freezer and found frost/ice buildup at the upper left hand corner of the evaporator coil unit that had actually encased the nearby wiring (The side-by-side entry and exit points of the coil were at the core of the frozen area).

The evaporator fan was running and almost the entire coil was unobstructed. It appeared that moist air had been entering from the openings behind the ice maker (which is not leaking and functioning fine) and permitting the accumulation.

I used a hair dryer to defrost and confimed I have flow from the drain hole below the coil to the catch pan underneath the refrigerator. I did note evidence of a prior long term plugged hole (rust on the back lower center of the freezer panel I removed.). It is possible the hole was plugged until I began using the hair dryer.

To overkill on the solution, I intend to replace the defrost timer, defrost thermostat and the seals on both refrigerator and freezer doors.

I understand that if I need an evaporator coil heater, I'm out of luck as the part is unavailable. I noted it was located at the bottom of the coil assembly and about as far away from the ice build up as it could be. I hope that indicates it is still functional.

Have I got it covered or can I/should I also consider sealing off the opening that appeared to be the entry point for the moist air to the backside of the panel?

Any other advice would be appreciated. Also, since this model used "Ref 12" refrigerant, if it comes down to needing a recharge, it's a conversion to a newer system, (or a new refrig) yes? Thanks!