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I–ECB29-20CB, -25CB – 208/230V THREE PHASE – SEQUENCE OF OPERATION
FIRST STAGE HEAT
1- When there is a call for heat, W1 of the thermostat
energizes the electric heat relays K32 and K34
with 24VAC.
2- When K32-1 closes, the blower is energized on
heating speed and economizer heat relay K43 is
energized (see 208/230VAC CB schematic).
3- When K32-1 and K32-2 closes, assuming the N.C.
primary (S15) and secondary (S20) limit switches
are closed, electric heat elements HE1 and HE2
are energized.
4- When K34-1 closes, assuming the N.C. primary
(S15) and secondary (S20) limit switches are
closed, electric heat element HE3 is energized.
SECOND STAGE HEAT
(remove jumper between W2 and R)
5- When K34-2 closes, the unit is ready for a second
stage heat demand. W2 of the thermostat sends a
second stage heat demand, energizing the electric
heat relays K33 and K35 with 24VAC.
6- When K33-1 closes, the blower (if not energized)
is energized on heating speed and economizer
heat relay K43 is energized (see 208/230VAC CB
schematic).
7- When K33-1, K35-1, and K35-2 contacts close, as-
suming the N.C. primary (S15) and secondary (S20)
limit switches are closed, electric heat elements
HE4, HE5, and HE6 are energized.
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