86
SEQUENCE OF OPERATION (cont.)
If the unit is occupied and t he fan is on, the damper will
operate at minimum position. Otherwise, the damper will
be cl osed.
If field installed accessory CO
2
sensors are connected to
the EconoMi$er IV and X control, a dem and cont rolled
ventilation strategy will begin to operate. As the CO
2
leve l in the zone inc reases above the CO
2
setpoint, the
minimum position of the damper will be increased
proportionally. As the CO
2
level decreases because of the
increase in fresh air, the outdoor air damper will be
proportionally closed. For EconoMi$er IV and X
operation, there must be a thermostat call for the fan (G).
If the unit is occupied and t he fan is on, the damper will
operate at minimum position. Otherwise, the damper will
be cl osed.
When the EconoMi$er IV and X control is in the occ upied
mode and a call for cooling exists (Y1 on the thermostat),
the control will first check for indoor fan operation. If the
fan is not on, then cooling will not be activated. If the fan
is on, then the control will open the EconoMi$er IV and X
damper to the minimum position.
On the initial power to the EconoMi$er IV and X control,
it will take the damper up to 2 1/2 minutes before it
begins to position itself. After the initial power--up,
further changes in damper position can take up to 30
seconds to initiate. Damper movement from full closed to
full open (or vice versa) will take between 1 1/2 and 2 1/2
minutes. If free cooli ng can be used as determined from
the appropriate cha ngeover command (switch, dry bul b,
enthalpy curve, differential dry bulb, or differential
entha lpy), the n the control will modulate the dampers
open to maintain the mixed air temperature setpoint at
50_F(10_C) to 55_F(13_C). If there is a further demand
for cooling (cooling second stage -- Y2 is energized), then
the control will bring on compressor stage 1 to maintain
the mixed air temperature setpoint. The EconoMi$er IV
and X damper will be open at maximum posit ion.
2--Speed Note: When operating in ventilation mode only,
the indoor fa n motor will automatically adjust to 2/3rd of
the total cfm established.
Heating
The sequence of operation for the heating is the same as
an electromechanical unit with no economizer. The only
difference is how the economizer acts. The economizer
will stay at the Economizer Minimum Position while the
evapora tor fan is operating. The outdoor air dampe r is
closed when t he indoor fan is not operating.
Optional Humidi--MiZer Dehumidification System
Units with the factory equippe d Humidi--MiZer option are
capable of providing multiple modes of improved
dehumidification as a variation of the normal cooling
cycl e. The Humidi--MiZer opt ion includes additi onal
valves in the liquid line and discharge line of each
refrigerant circuit, a small reheat c ondenser coil
downstream of the evapora tor, and Motormaster
variable--speed control of some or all outdoor fans.
Operation of the revised refrigerant circuit for each mode
is described below.
The Humidi--MiZe r system provides three sub--modes of
operat ion: Cool, Reheat1, and Reheat2.
Cool mode -- provides a normal ratio of Sensible and
Latent Cooling effect from the evaporator coil.
Reheat1 -- provides increased Late nt Cooling while
slightly reducing the Sensible Cooling effect.
Reheat2 -- provides normal Latent Cooling but with null
or minimum Sensible Cooling effect delivered to the
space.
The Rehea t1 and Reheat2 modes are available when the
unit is not in a Heating mode and when the Low Ambient
Lockout switch is closed.
The following diagrams depict piping for Single Stage
cooling units.
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