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F−ECB29-25CB − 208/230V SINGLE 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 (K20-2) is
energized (see unit schematic 26).
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.
SECOND−STAGE HEAT
(remove jumper between W2 and R)
4. When K34-1 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
K116 with 24VAC.
5. 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).
6. When K33-2 and K116-1 close, assuming the N.C.
primary (S15) and secondary (S20) limit switches
are closed, electric heat elements HE3 and HE6 are
energized.
THIRD− STAGE HEAT
(remove jumper between W3 and R, if using third stage)
7. When K34-2 closes, the unit is ready for a third stage heat
demand. W3, if available, of the thermostat sends a third
stage heat demand, energizing the electric heat relay K35
with 24VAC.
8. When K35-1 and K35-2 close, assuming the N.C.
primary (S15) and secondary (S20) limit switches
are closed, electric heat elements HE4 and HE5 are
energized.
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