Carrier 38AUQ 16 Series, Installation, Start-Up And Service Instructions Manual

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27
Compressor Protection
Compressor Overcurrent —
The compressor has internal limbered motor protection.
Compressor Overtemperature Protection (IP) —
The compressor has an internal protector to protect it
against excessively high discharge gas temperatures.
Crankcase Heater —
The heater prevents refrigerant migration and compressor oil
dilution during shutdown whenever compressor is not
operating. The heater is wired to cycle with the compressor;
the heater is off when compressor is running, and on when
compressor is off.
The crankcase heater will operate as long as the power
circuit is energized. The main disconnect must be on to
energize the crankcase heater.
IMPORTANT
: Never open any switch or disconnect
that energizes the crankcase heater unless unit is
being serviced or is to be shut down for a prolonged
period. After a prolonged shutdown on a service job,
energize the crankcase heater for 24 hours before
starting the compressor.
High Pressure Switch —
The system is provided with a high pressure switch
mounted on the discharge line. The switch is
stem-mounted and brazed into the discharge tube. Trip
setting is 630
±
10 psig (4344
±
69 kPa) when hot. Reset
is automatic at 505
±
20 psig (3482
±
140 kPa).
Loss of Charge Switch —
The system is protected against a loss of charge and low
evaporator coil loading condition by a loss of charge switch
located on the liquid line and a freeze protection thermostat
on the indoor coil. The switch is stem-mounted. Loss of
Charge Switch trip setting is 27 psig
±
3 psig (186
±
21 kPa).
Reset is automatic at 44
±
5 psig (303
±
35 kPa).
The factory installed loss of charge pressure switch (LOC)
has open/close settings which do not provide indoor coil
freeze protection. The control provides a location on
terminal board TB2 to add a field supplied indoor coil freeze
protection switch, if additional protection is wanted. The
freeze protection switch can be wired into the 24VAC
control circuit in series with the high pressure switch and
loss of charge switch as shown in Fig. 22. Note that the wire
to the compressor contactor must be moved from the LPS
terminal to the FPT terminal, as shown.
A recommended indoor coil freeze protection switch is part
# HH18HB015 (30
_
±
5
_
F open, 45
_
±
5
_
F close) which
can be mounted on a return bend of the indoor coil. For
dual--circuits, a separate switch si used for each half of the
indoor coil. And are wired as shown in Fig. 22
Outdoor Fan Motor Protection —
The outdoor fan motor is internally protected against
overtemperature.
Control Circuit, 24-V —
The control circuit is protected against overcurrent
conditions by a circuit breaker mounted on control
transformer TRAN. Reset is manual.
Commercial Defrost Control
The Commercial Defrost Control Board (DFB)
coordinates thermostat demands for supply fan control, 1
or 2 stage cooling, 1 or 2 stage heating, emergency
heating and defrost control with unit operating sequences.
See Fig. 23 for board arrangement.
The DFB is located in the 38AUQ’s main control box (see
Fig. 24). All connections are factory-wired. Refer to
Table 8 for details of DFB Inputs and Outputs.
C1
HPS LPS FPT
HPS LPS FPT
HPS1
LOC1
or
LPS1
FPT1
HPS2 LOC2
or
LPS2
FPT2
CIRCUIT 1
CIRCUIT 2
C2
NOTE: Move compressor contactor wire
from right-side LPS terminal
to right-side FPT terminal
C10822
Fig. 22 -- Field Wiring of Indoor Coil Freeze Protection Switch (FPT)(Dual Circuit Shown)
38A
U
Q