The wiring diagram in the tech sheet doesn’t give the pin numbers for the defrost timer but it appears that in cooling mode, the defrost timer gets it power through the defrost heater and the defrost thermostat (supplier example only to show location and possible cost).
See the Steps to enter electronic defrost control test mode (if applicable) (in the middle of the tech sheet) to check if the defrost thermostat opens and closes.
Here’s a video that may help with testing the defrost thermostat. If the defrost thermostat is faulty search for WPW10225581 to get results for suppliers that suit you.
Hopefully this is of some help.
In defrost mode, is the heater actually getting warm?
Is the evaporator fan working in cooling mode?
In cooling mode check for voltage on timer terminal 2 (pink). If no good check on the defrost thermostat. If still no good check on the heater.
Here’s an image how I think that it works.
In cooling mode the red arrows show the path of the current to operate the timer. I think that the heater won’t get warm because there is not enough current for it but is enough for the timer.
When the timer operates after 8 hours to start the defrost, the heater is turned on because the timer contacts have operated bypassing the timer motor (green arrow through heater). However there is also still a voltage coming from the evap fan circuit (see green arrow through the evap fan which goes through the timer motor) which should keep the timer working but maybe not the evap fan.
After 21 minutes the timer contacts release and turn off the heater
(click on image to enlarge)