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SEQUENCE OF OPERATION EHA7.5, 15, 22.5, 30, 45, 60 kW - G, J, M and Y
G, J and M Voltage
1 Terminal strip TB3 is energized when the unit discon
nect closes. TB3 supplies line voltage to electric heat
elements HE1, HE2, HE3 and HE4. HE1 and HE2 ele
ments are protected by F3 and HE3 and HE4 elements
are protected by fuse F42.
First Stage Heat:
2 Heating demand initiates at W1 in the thermostat.
3 24VAC is routed through A55 Unit Controller. After
A55 proves N.C. primary limit S15, contactor K15 is
energized.
4- N.O. K15-1 contacts close energizing HE1 and HE2.
Second Stage Heat:
5 With first stage heat operating, an additional heating
demand initiates W2 in the thermostat.
6 A second stage heating demand is received by A55
control module.
7 A55 energizes contactor K16.
8 N.O. K16-1 contacts close energizing HE3 and HE4.
Y Voltage
1 Terminal strip TB3 is energized when the unit discon
nect closes. TB3 supplies line voltage to electric heat
elements HE1, HE2, HE3, HE4, HE5 and HE6.
First Stage Heat:
2 7.5 - 45 KW - Heating demand initiates at W1 in the
thermostat.
3 24VAC is routed through A55 Unit Controller. After
A55 proves N.C. primary limit S15 and S157, contac
tor K15 is energized.
4- N.O. K15 contacts close energizing HE1.
2 60KW - Heating demand initiates at W1 in the thermo
stat.
3 24VAC is routed through A55 Unit Controller. After
A55 proves N.C. primary limit S157, contactor K242 is
energized.
4- N.O. K242 contacts close energizing HE3 and HE4.
Second Stage Heat:
5 22.5 - 45 KW - With first stage heat operating, an addi
tional heating demand initiates W2 in the thermostat.
6 A second stage heating demand is received by A55
control module. After A55 proves N.C. primary limit
S58 and S159, contactor K16 is energized.
7 N.O. K16 contacts close energizing HE2 (22.5 and
30KW units only) and HE5 and HE6 (45 KW units only).
5 60KW - With first stage heat operating, an additional
heating demand initiates W2 in the thermostat.
6 A second stage heating demand is received by A55
control module. After A55 proves N.C. primary limit
S160 and S161, contactor K16 is energized.
7 N.O. K16 contacts close energizing HE5 and HE6.
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