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SEQUENCE OF OPERATION
HEAT PUMP
1 - A55 Unit Controller receives W1 heating demand
2 -
3 -
energized.
4 -
N.C. K1-52 opens de-energizing HR1.
5 -
energized.
7 -
N.C. K2-52 opens de-energizing HR2.
EHA-15, 30, 45, 60, 90 - Y & G
NOTE:Two electric heat sections are used in all 15kW
through 90kW heaters. The heat sections are labeled rst
electric heat section (left side) and second electric heat
section (right side). See gure 16.
NOTE: In the case of EHA 15 and 30kW, the second heat
section (right side) is a slave (only has electric heat ele-
ments and a limit). Line voltage is supplied to elements in
both heat section one (left side) and two (right side) by the
contactors in heat section one (left side).
HEATING ELEMENTS:
1 - Terminal strip TB3 is energized when the unit
disconnect closes. TB3 supplies line voltage to
electric heat elements HE1 through HE14. Each
heating element is protected by fuse F3.
FIRST STAGE HEAT:
2 - Heating demand initiates at W1 in thermostat.
3 - 24VAC is routed to the main control module A55.
After A55 proves N.C. primary limits S15 (heat
K9 are energized.
4 -
of elements in heat section one (left side) to be
energized.
5 -
K17.
of elements in heat section two (right side) to be
energized.
SECOND STAGE HEAT:
7 -
heating demand initiates at W2 in the thermostat.
24VAC is routed through the main control module
9 -
of elements in heat section one (left side) to be
energized.
10 -
11 -
of elements in heat section two (right side) to be
energized.
END OF SECOND STAGE HEAT:
12 -
thermostat is de-energized.
13 -
energized.
14 - The second set of electric heat elements in heat
sections one (left side) and two (right side) are de-
energized.
END OF FIRST STAGE HEAT:
15 -
thermostat is de-energized.
Electric heat contactors K15 and K17 are de-
energized.
17 -
sections one (left side) and two (right side) are de-
energized.
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