Three-Phase Defrost Sequence - Lennox HP21 Unit Information

L−THREE-PHASE DEFROST SEQUENCE
1− When the defrost control determines a defrost needs to be initiated it
closes an internal relay connected to DEF RLY terminal. Relay K4 is
energized. Relay K4 controls defrost.
2− When relay K4 energizes, K4-1 switches to energize the reversing
valve, K4-2 opens to de-energize the outdoor fan and K4-3 closes to
energize auxiliary heat.
4
2
3
1
S1, S2 DENOTE
TERMINAL
DESIGNATIONS
FIGURE 37
3− Refer to the unit component section of this manual for detailed defrost
control operation. Defrost is terminated when relay K4 is de-ener-
gized.
4− When thermostat demand is satisfied or if thermostat is switched OFF
or switched to heating mode, all outdoor unit operation stops after a
delay of 3 seconds. TSC then completely resets (erase accumulated
faults) before cycling through the 5 minute timed-off delay.
Page 39
Thermostat Demand Satisfied