[Switzman]

Side by side refrigerator, evap coils are freezing up, rendering refrig side useless. Compressor & evap fan seem to run continuously. I suspect either the defrost timer or defrost heater have failed. The defrost timer for this model is on a PC board down below in front of unit. I have a multimeter but have no idea how to test it. Any ideas? Also, what kind of ohmmeter reading should I be getting on the heater?

[woodchuck]

check the heater and the defrost thermostat. All that's left after that is the board.

Refrigerator Repair Guide: How To Fix a Refrigerator - ACME HOW TO.com

[denman]

Looks like you have an adaptive defrost control
This may help
Adaptive defrost systems for newer refrigerators with electronic defrost controls

If your freezer fan goes off then normally you are in a defrost cycle