Page 49
Sequence of Operation
EHA 7.5, 15, 22.5, 30W − Y, G, J and M
NOTE: This sequence of operation is for all Electric
Heat kW ratings Y through J voltages. Each step of op-
eration is numbered and can be followed in sequence
on the diagrams. Operation for G, J, and M voltages will
be the same.
HEATING ELEMENTS:
1 − Terminal Strip TB3 is energized when the unit discon-
nect closes. TB3 supplies line voltage to electric heat
elements HE1 through HE7. Each element is protected
by fuse F3.
FIRST STAGE HEAT:
2 − Heating demand initiates at W1 in thermostat.
3 − 24VAC is routed through TB34 to the main control
module A55. After A55 proves N.C. primary limit S15
and secondary limit S20, the electric heat contactor
K15 is energized.
4 − N.O. contacts K15−1 closes allowing the first bank of
elements to be energized. Indoor blower is energized
with no time delay.
SECOND STAGE HEAT:
5 − With the first stage heat operating, an additional heat-
ing demand initiates at W2 in the thermostat.
6 − 24VAC is routed through the main control module A55,
which in turn energizes the electric heat contactor K16.
7 − N.O. contacts K16−1 close allowing the second set of
elements to be energized.
END OF SECOND STAGE HEAT:
8 − Heating demand is satisfied. Terminal W2 in the ther-
mostat is de−energized.
9 − Electric heat contactor K16 is de−energized.
10− The second set of electric heat elements are de−ener-
gized.
END OF FIRST STAGE HEAT:
11− Heating demand is satisfied. Terminal W1 in the ther-
mostat is de−energized.
12− Electric heat contactor K15 is de−energized.
13− The first set of electric heat elements are de−energized.
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