Copy following links:
http://waterheatertimer.org/Paragon-timers-and-manuals.html#sethttp://waterheatertimer.org/images/8145-work-image.jpg
Install defrost trippers on dial at times you want defrost to begin.
8145-20 is generally time initiated, and temperature or pressure terminated... but you can set the defrost duration on smaller center dial..and this setting will terminated defrost cycle mechanically if the pressure or temperature sensor fail. Then manually rotate timer dial until current time lines up with time marker in upper left side.
Gene
h. If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7