Thank you, denman! I've printed and saved the .pdf you sent, and will try forcing a defrost. Also, the sheet gives the protocol for checking the defrost thermostat using the keypad; I'll try that too.

The customer's complaint was warm fridge, cold freezer (this is a bottom-freezer model, with icemaker. It has digital touch controls located in the French-door refrigerator section). I jumped to conclusions and replaced the motorized damper which regulates fridge temperature in this model; I then discovered that the evaporator was completely iced up. After defrosting it manually w/heat gun, I checked the heater resistance; it's o-k. Further research revealed that there is no traditional defrost clock; it uses a module which I believe is part of the digital temp. control setup. I should note that the unit was subjected to multiple power failure events due to a prolonged northeast storm (happens a lot here on Cape Cod). What are the chances that the module is defective, as against the likelihood of a defrost thermostat gone bad? The thermostat is hard to check once the unit is defrosted to the point where you can get to the connections....