Lennox ZCC Series Unit Information page 48

Sequence of Operation - EHA 7.5, 15, 22.5, 30, 45, 60 kW - Y and G, J, M
NOTE: This sequence of operation is for all Electric Heat
kW ratings Y through J voltages. Each step of operation
is numbered and can be followed in sequence on the di-
agrams. Operation for G, J, and M voltages will be the
same.
HEATING ELEMENTS:
1 - Terminal Strip TB3 is energized when the unit
disconnect closes. TB3 supplies line voltage to
electric heat elements HE1 through HE6. Each
element is protected by fuse F3, F42, F43, or F44.
FIRST STAGE HEAT:
2 - Heating demand initiates at W1 in thermostat.
3 - 24VAC W1 signal is routed from the thermostat
through TB1 and P2-2. After S15 N.C. primary limit
and S19 limit is proved, the electric heat 1 contactor
K15 is energized.
4 - If S20 and S157 (S158 on Y-volt units) secondary
electric heat limits remain closed, HE1 and HE2
(HE3 and HE4 on Y-volt units) electric heat is
energized.
SECOND STAGE HEAT:
5 - Heating demand initiates at W2 in thermostat.
6 - 24VAC W2 signal is routed from the thermostat
through TB1 and P2-7. Electric heat contactor K16
is energized.
7 - If S158 and S159 (S159, S160 and S161 on Y-volt
units) secondary electric heat limits remain closed,
HE3 and HE4 electric heat is energized.
Page 48