How to Troubleshoot & Replace Whirlpool AP6009314 / WP4387499 Defrost Thermostat

I replaced the defrost heater element and the thermostat. There was nothing wrong with the thermostat, but I decided to replace it due to the age and location ( next to the defrost heater). 

Not knowing which might be bad I first replaced the Timer (easiest to replace). Achieving no appreciable difference after 24 hours I then replaced the Defrost Thermostat. This of course involved emptying the freezer into coolers to get to its location. After the freezer was emptied it was a simple job of removing two panels with a total of about 4 screws and several push-pin type retainers to get to the Thermostat. Simple job of cutting 2 wires and installing the new Thermostat with crush type wire connectors. Reinstall the panels and reload the freezer and all is well and freezing as is normal. Freezer's age 28 years bought new in 1993, Whirlpool. 

Power was on, compressor off. Manually turned defrost timer, compressor started. Ended up changing compressor relay, caps, overload. Replaced defrost timer, defrost bi-metal tested ok so have a spare now. Even with compressor running unit would not cool down much. Ended up using dry ice to store all the food in Styrofoam iceboxes overnight when it was clear we were going to lose all the food. Pulled freezer section air shroud, found evaporator coils clogged with ice, air door to frig also clogged with ice, Defrosted with heat gun. Working good now. - 10 in freezer 38 in frig. I thought the compressor was dying but the resistances checked out okay. The condenser coils don't get very warm on this unit which fooled me into thinking maybe the compressor was weak. Not so, these units run at relatively low 190-200 watts for most of the time. Especially now with the hot spell we're having. Considering wiring the defrost circuit with a "vacation" switch to insure it doesn't trigger the defrost coil when I am away. Keeping an eye on it. 

After troubleshooting, determined it was the thermostat. Appliance parts pros had the best deal for the $$ I felt so I ordered it. Quick shipping. As far as the install, the instructions tell you to cut the old one out and then splice both sides and use a connectors. I found it ALOT easier to remove the whole thing from the freezer and spice/connect that way so your not fighting the crampness/tightness of freezer. The thermostat is plugged into the freezer with a simple connector. Just press the indentation/tab and it pulls right out. Splice/crimp and then put right back in. Easy and took less than 5 minutes. Took me longer to take the stuff off to access the thermostat than it did to do the replacement.