Problem with GE GSS22SGRFSS Stainless Steel Side by Side Refrigerator

I want to test the defrost thermostat in GE GSS22SGRF SS but it seems to be wired into the heater and, it appears, the bulb receptacle. Can continuity be tested when circuit is integrated with others? Or do I need to snip it off?

Freezer cold, refrig not. Happened a couple of years ago and replaced heater. Good since then. Heater is still okay. 18 ohms on continuity. Came on once when I was looking. Not sure why.

Evaporator thermistor – 15.5 ohms (in ice water for 5-7 minutes). I understand 16.3k is optimal. Is 15.5 out of range?

When the defrost heater needed replacement a couple of years ago, thawing coils would give about two weeks before it needed thawing again. This time the evaporator coils begin to frost up immediately – within seconds of plugging the refrigerator in. (Because freezer is empty?)

Damper door always open. Unplugged refrigerator, manually closed it, plugged rf back in, it opened immediately.

Front of divider between compartment was very warm, almost hot. Normal? Okay?