Defrost Cycle

Defrost Cycle
If the outdoor ambient conditions are such that frost forms on the
outdoor coil, the defrost control monitors the need for and
initiates and terminates defrost cycles as necessary to maintain
system performance.
The defrost control is time/temperature initiated and temperature
terminated with a maximum defrost time (time-out) of 10 minutes.
The time between defrost cycles is preset at 60-minute intervals
at the factory, but can be field adjusted between 30, 60, or 90
minutes. To adjust the time period between defrost cycles, see
“Adjust Time Between Defrost Cycles.”
The defrost control will initiate a defrost cycle when the selected
time period has elapsed and the defrost sensor sees a
temperature below freezing. At the start of a defrost cycle, the
defrost control will energize the reversing valve solenoid, shifting
the reversing valve and de-energizing the outdoor fan. The
defrost relay will also close, energizing temporary heat for
increased comfort during defrost (if the indoor unit is so
equipped). The heat pump will remain in defrost until the defrost
sensor has determined that the frost has been removed from the
coil or a 10-minute period has elapsed, whichever comes first