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B. Ventilation Sequence
If unit is equipped with an economizer, the damper will open
to the minimum position whenever the evaporator fan runs.
The damper motor will be energized with 24 vac power
and damper will drive open until SW3 on the damper is de-
activated. The damper motor will stop and damper will
remain in the minimum ventilation position until the evapo-
rator fan is shut off. When the evaporator fan is shut off, the
damper motor is again energized and the damper runs closed
until SW2 is activated and the damper motor turns off.
When unit is equipped with an economizer, additional out-
door air can be brought in through the damper to provide
cooling. If the unit calls for cooling and the outdoor-air tem-
perature is below the outdoor-air thermostat (OAT) setting
or the outdoor-air enthalpy is below the enthalpy control (EC)
setting, the damper motor starts. The damper drives open
until it reaches full open and SW1 is activated. When SW1 is
deactivated, the damper motor stops. When the cooling load
is satisfied, or outdoor air is no longer below the OAT or EC
setting, the damper returns to the minimum position.
If the supply-air thermostat (located on the evaporator-fan
housing) senses a supply-air temperature less than 50 F, the
damper closes until the supply-air temperature is above
50 F.
Table 7 — Fan Rpm at Motor Pulley Settings*
UNIT
581B
MOTOR PULLEY TURNS OPEN
0
1
⁄
2
11
1
⁄
2
22
1
⁄
2
33
1
⁄
2
44
1
⁄
2
55
1
⁄
2
6
036 1090 1055 1025 990 960 925 890 860 825 795 760 — —
048 1185 1150 1115 1080 1045 1015 980 945 910 875 840 — —
060 1460 1425 1385 1350 1315 1275 1240 1205 1165 1130 1095 1055 1020
072 1585 1540 1490 1445 1400 1350 1305 1260 1210 1165 1120 — —
*Approximate fan rpm shown.
Table 8 — Evaporator Fan Motor Data
UNIT
581B
PHASE
MAXIMUM
UNIT
VOLTAGE
MAXIMUM
CONTINUOUS AMP
BHP* DRAW
036
Single 1.20 208/230 5.4
Three 1.20
208/230 5.4
460 2.4
575 2.4
048
Single 1.20 208/230 5.4
Three 1.20
208/230 5.4
460 2.4
575 2.4
060
Single 1.80 208/230 9.7
Three 1.80
208/230 6.4
460 2.9
575 2.9
072 Three 2.40
208/230 6.4
460 2.9
575 2.9
LEGEND
Bhp — Brake Horsepower
*Extensive motor and electrical testing on these units ensures that the full horsepower range of the
motors can be utilized with confidence. Using your fan motors up to the ratings shown in this table will
not result in nuisance tripping or premature motor failure. Unit warranty will not be affected.
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