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A24 diagram with B9 diagram
ECH16-185/255/275/300 75kW 460V & 575V Sequence
Operation Sequence: A24 Section and B9 Sections
(75kW 460V or 575V electric heat wired to CHA16-1853)
1- Noheat relay K29 is not used in this application and is omitted. Since this circuit remains
open, primary limit S63 remains unused.
2- 1st stage heating demand closes W1. W1 energizes pilot relay K77. K771 closes.
3- When K771 closes, heating pilot relay K9 is energized. K91 switches and K93 closes.
K92 closes to enable K19.
4- When K91 switches, indoor blower contactor K3 is energized (and optional power ex
haust fan relay K65 is enabled when K32 cotacts close).
5- When K93 closes, electric heat contactor K15 is energized. K151 closes.
6- When K151 closes, heating elements HE1 and HE2 are both energized. The elements are
arranged in a Wye" configuration for 460V or 575V operation.
7- Additional heating demand W2 energizes pilot relay K49. K49-1 closes.
8- When K491 closes, relay K19 is energized.
9- When K191 closes, time delay DL2 is energized. DL2 begins counting. After 30 seconds, DL2
closes.
10- When DL2 closes, contactor K16 and tiime delay DL4 are both energized. DL4 begins count
ing. After 30 seconds, DL4 closes.
11- When K161 closes, heating elements HE3 and HE4 are both energized.
12- When DL4 closes, contactor K17 is energized.
13- When K171 closes, heating element HE5 is energized.
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