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2. Fan status switch input should close. Note the unit will
not start unless the fan status input is closed.
3. Close Y1 input unit will stage up to 50 % capacity with
1 minute between stages.
4. Close Y2 input the unit will stage up to 100% capacity
with 1 minute between stages.
CV APPLICATION — C.TYP = 3
1. Start indoor fan motor.
2. Fan status switch input should close. Note the unit will
not start unless the fan status input is closed.
3. Close Y1 input unit. The control will control supply-air
temperature to CSP1 and stage capacity as required.
4. Close Y2 input. The unit will control supply-air tempera-
ture to CSP2 and stage capacity as required.
CV APPLICATION — C.TYP = 5
1. Start indoor fan motor.
2. Fan status switch input should close. Note the unit will
not start unless the fan status input is closed.
3. The control will use space temperature (Tempe ratures
SPT) vs space temperature set point (Set Point
COOL SPS.P) to decide to whether to control supply-
air temperature to CSP1 or CSP2, and will stage capacity
as required.
% CAPACITY INPUT — C.TYP = 7
1. Start indoor fan motor.
2. Fan status switch input should close. Note the unit will
not start unless the fan status input is closed.
3. The control will adjust unit capacity based on the 4 to
20mA Cool mA (INPUTS 4-20 CL.MA).
4. Actual capacity and desired capacity may be different due
to unit diagnostics.
OPERATION
Operating Limitations
AMBIENT LMITATIONS — See Table 16 for ambient
limitations.
Table 16 — 38AP Unit Ambient Limitations
Single Circuit
Dual Circuit
* Factory-installed option or field-installed accessory.
†Operation above listed temperature depends on the saturated suction tem-
perature the unit is operating at. Refer to ECAT for exact limitations.
VOLTAGE (ALL UNITS)
Main Power Supply
— Minimum and maximum acceptable
supply voltages are listed in the Installation Instructions.
Unbalanced 3-Phase Supply Voltage — Never operate a motor
where a phase imbalance between phases is greater than 2%.
To determine percent voltage imbalance:
The maximum voltage deviation is the largest difference
between a voltage measurement across 2 legs and the average
across all 3 legs.
Example: Supply voltage is 240-3-60.
AB = 243 v
BC = 236 v
AC = 238 v
1. Determine average voltage:
2. Determine maximum deviation from average voltage:
(AB) 243 – 239 = 4 v
(BC) 239 – 236 = 3 v
(AC) 239 – 238 = 1 v
Maximum deviation is 4 v.
3. Determine percent voltage imbalance:
This voltage imbalance is satisfactory as it is below the
maximum allowable of 2%.
Control Circuit Power
— Power for the control circuit is
supplied from the main incoming power through a factory-
installed control power transformer (TRAN1) for all models.
Field wiring connections are made to LVT terminal board.
Operation Sequence — During unit off cycle, if power
is maintained to the unit and the EMERGENCY ON/OFF
switch is left in the OFF position, the compressor crankcase
heaters will be energized.
The unit is started by putting the ENABLE/OFF/REMOTE
CONTACT switch in the ENABLE or REMOTE CONTACT
position. When the unit receives a call to run (either from the
internal control, or CCN network command or remote contact
closure), the unit stages up in capacity to maintain either supply
air temperature or space temperature. The first compressor
starts 1
1
/
2
to 3 minutes after the call for cooling.
The lead circuit can be specifically designated on all models
or selected based on compressor run hours and starts depend-
ing on field configuration. The unit control will override this
selection under certain starting conditions to properly maintain
oil return to the compressors. The MBB controls fan stages to
maintain the head pressure set point and will automatically ad-
just unit capacity as required to keep compressors from operat-
ing outside of the specified envelope. There are no pumpout or
pumpdown sequences on these units.
The liquid line solenoid valve is energized anytime a com-
pressor is operating in the circuit and also when the circuit is
OFF and the OAT is less than the SST. The liquid line solenoid
valve is de-energized 5 seconds after the circuit stops and also
when the circuit is OFF and the OAT is greater than the SST
plus 2° F. Each circuit operates independently.
38APS
UNIT
SIZE
MINIMUM LOW
AMBIENT
(Standard Unit)
MINIMUM LOW AMBIENT
MOTORMASTER
®
CONTROL*
MAXIMUM
AMBIENT†
025-050 45 F (7.2 C) 20 F ( 28.9 C) 122 F (50 C)
38APD
UNIT
SIZE
MINIMUM LOW
AMBIENT
(Standard Unit)
MINIMUM LOW AMBIENT
MOTORMASTER
CONTROL*
MAXIMUM
AMBIENT†
025-040 32 F (0 C) 20 F ( 28.9 C) 122 F (50 C)
050-060 25 F ( 3.9 C) 20 F ( 28.9 C) 122 F (50 C)
070-100 32 F (0 C) 20 F( 28.9 C) 122 F (50 C)
% Voltage Imbalance = 100 x
max voltage deviation
from avg voltage
average voltage
–
–
–
–
–
–
–
–
–
Average voltage =
243 + 236 + 238
3
=
717
3
= 239
% Voltage Imbalance = 100 x
4
239
= 1.7%
IMPORTANT: If the supply voltage phase imbalance is
more than 2%, contact your local electric utility company
immediately. Do not operate unit until imbalance condition
is corrected.