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H−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 (K20-2) is
energized (see unit schematic figure 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.
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,
assuming the N.C. primary (S15) and secondary (S20)
limit switches are closed, electric heat elements HE4,
HE5, and HE6 are energized.
