Carrier 50EJQ Installation, Start-Up And Service Instructions Manual page 28

The IAQ sensor can be configured to either low or high
priority. The priority value can be changed by the user. The
default is low.
Low Priority — When the priority is set to low, the initial
control is to the IAQ set point, but the outside air damper
position will change to its minimum position when the fol-
lowing conditions occur:
• units with sensor — when the space temperature is greater
than the occupied cooling set point plus 2° F or when the
space temperature is less than the occupied heating set point
minus 2° F.
• units with thermostat — when the supply-air temperature
is less than the supply-air temperature set point minus
8° F or when the supply-air temperature is greater than the
supply air temperature set point plus 5° F for 4 minutes.
• When the outdoor air quality is greater than the outdoor
air quality set point (ppm)
High Priority — When the priority is set to high, the IAQ
set point controls the outside air damper exclusively, with
no regard to comfort conditioning.
SPACE TEMPERATURE OFFSET — An accessory space
temperature sensor (T-56) will allow an offset of the space
temperature set point ± 5° F. The 4 to 20 mA signal corre-
sponds to a 0° to 20° F offset. The reset ratio set point is
used to modify the offset temperature range. See Fig. 36 for
space temperature sensor wiring.
NOTE: Sensor part number is CEC0121503-01.
Fig. 36 — Space Temperature Sensor Wiring
DISABLING THE ECONOMIZER — For applications where
the economizer will not be used (areas of high humidity),
the economizer will need to be disabled. Be sure to turn off
electrical power before attempting this procedure. The econo-
mizer is best disabled by breaking the splice connecting the
violet wire coming from T24 on the base module board and
the red wire coming from T29 on the base module board.
The splice is made where the OAT (outdoor air ther-
mistor) is located (at the right hand outdoor air damper area).
Remove the wire nut from the violet to red wire splice. Cap
off both wires so the connection is broken. When the con-
nection is broken, the base module is fooled into thinking
that the enthalpy is not acceptable and economizer operation
is disabled.
CAPACITY CONTROL, COOLING — The cooling capac-
ity staging table is shown in Table 16.
Table 16 — Cooling Capacity Staging Table,
Units with 2 Compressors
STAGES
Compressor 1 Off
Compressor 2 Off
NOTE: On units that require additional unloading, add suction pres-
sure unloaders on Compressor 1 only.
FIELD TEST — The field test program is initiated by mov-
ing up DIP switch no. 4 to the OPEN position. The outdoor-
air damper will close. The control allows 90 seconds for the
damper to close in case it was in the full open position. Next,
the indoor-fan contactor will be energized, and the outside-
air damper will begin to open to its default value of 20% and
stay at that position for a short period of time. The outdoor-
air damper will then open to its full open position and stay
at that position for a short period of time. The outdoor-air
damper will then close.
If the unit is equipped with power exhaust, stage 1 will be
energized for 5 seconds. If the unit is configured for stage 2
of power exhaust, stage 2 will be energized for 5 seconds
after the first stage is deenergized.
The first stage of heat will be energized for 30 seconds,
after which the second stage heat will be energized for an
additional 30 seconds. Heat is then deenergized.
The last step is the Cooling mode. Outdoor-fan contactor
no. 1 is energized. This is followed by each stage of cooling
energized with a 10-second delay between stages. After this
is complete, outdoor-fan contactor no. 2 is energized for
10 seconds.
The compressors will now deenergize, followed by the
outdoor-fan contactors and indoor-fan contactors.
The field test is then complete.
TIME GUARD CIRCUIT — The Time Guard function (built
into the unit control module board) maintains a minimum
off time of 5 minutes and a minimum on time of 10 seconds.
CRANKCASE HEATER — The unit main power supply must
remain on to provide crankcase heater operation. The crank-
case heater in each compressor keeps oil free of refrigerant
while compressor is off.
HEAD PRESSURE CONTROL — Each unit has a fan
cycling, outdoor thermostat to shut off outdoor-fan motor(s)
at 55 F. The head pressure control permits the unit to operate
with correct condensing temperatures down to 35 F outdoor-
air temperature if the economizer is disabled.
MOTORMASTER III DEVICE — The Motormaster III
Solid-State Head Pressure Control is a field-installed acces-
sory, fan speed control device actuated by a temperature
sensor. The Motormaster III device is specifically designed
for use on Carrier equipment and controls the outdoor-
fan motor speed in response to the saturated condensing
temperature. For outdoor temperatures down to −20 F, the
Motormaster III device maintains condensing temperature at
100 F.
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1
0 2
ECONOMIZER
Off On
Off Off
3
On
On