Lennox ALLIED Commercial TCA180S2B Standard Manual page 49

Sequence of Operation −EHA15, 30, 45, 60, 90kW − Y and G, J, M
NOTE: This sequence of operation is for all Electric
Heat kW ratings Y, G, J and M voltages.
HEATING ELEMENTS:
1− Terminal Strip TB15 supplies power to TB3. TB3 sup-
plies line voltage to electric heat elements HE1 through
HE14. Each element is protected by fuse F3.
FIRST STAGE HEAT:
Heating demand initiates at W1 in thermostat.
2 − 24VAC is routed from T2, proving N.C. primary limits
S15 (first heat section) and S107 (second heat sec-
tion). Voltage then energizes contactors K15 and K17.
24VAC is routed through module A45 P88 energizing
relay K9. N.O. K9−1 close.
3 − N.O. contact K15−1 closes allowing the first bank of
elements to be energized. N.O. K17−1 closes allowing
the second bank of elements to be energized.
SECOND STAGE HEAT:
With the first stage heat operating, an additional heat-
ing demand initiates at W2 in the thermostat.
4 − Relay K19 is energized. N.O. contacts K19−1 close en-
ergizing timer DL2.
5 − After a 30 second delay, DL2 closes energizing contac-
tor K16 and timer DL5.
6 − N.O. contacts K16−1 close allowing the third bank of
elements to be energized.
7 − After a 30 second delay, DL5 closes energizing contac-
tor K18. K18−1 closes allowing the fourth bank of ele-
ments to be energized.
END OF SECOND STAGE HEAT:
Heating demand is satisfied. Terminal W2 in the ther-
mostat is de−energized.
8 − Electric heat contactors K16 and K18 are de−ener-
gized.
9 − The fourth and third set of elements are de−energized.
END OF FIRST STAGE HEAT:
Heating demand is satisfied. Terminal W1 in the ther-
mostat is de−energized.
10 − Electric heat contactors K15 and K17 are de−ener-
gized.
11 − The second and first set of electric heat elements are
de−energized.
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