Hi--

I'm troubleshooting my parents' Kenmore 795.72053.118 refrigerator. For the first several years of operation, it worked fine, but as of 1-2 years ago, the fridge evaporator coil unit started getting covered with ice. They've been manually defrosting it every 6 months, but it's obviously a pain to do so.

The system doesn't show any errors on the display. I've checked the Fuse-M (0 ohms), the heater resistance (~82 ohms), the defrost temp sensor (in spec). I've also checked the voltage at the heater--this is where things get interesting:

• When I power the fridge on, the heater gets a full 110VAC for a few moments, then turns off (likely because the fridge temp sensor is above the threshold for needing to defrost)
  
• If I put the fridge into forced defrost mode (press the test button on the main PCB on the fridge rear for 1 sec, then push it again 2 times, and the fridge display reads "33 33"), per the service manual, both fridge and freezer defrost heaters should kick on--but only the freezer one does.

So while the main PCB is able to turn the fridge defrost heater on (briefly during fridge startup), it doesn't do so during the diagnostic mode when it's supposed to do so.

I'm guessing I just need to replace the main PCB--it's $220 on Amazon...but was wondering if anyone had any other thoughts--I wish I had a schematic--I hate to change a $220 PCB when it could be as simple as a $3 relay.

Thank you for your help!
Sandheep