Carrier 48DU Installation Instructions Manual page 30

SYSTEMS COMMUNICATION FAILURE
If communication with the Infinity Control is lost with the UI,
the controls will flash the appropriate fault codes. Check the
wiring to the UI, indoor and outdoor units.
MODEL PLUG
The HP/AC control board must have a valid model plug to
operate. If a valid model plug is not detected, it will not operate
and the control will flash the appropriate fault code, shown in
Table 5.
PRESSURE SWITCH PROTECTION- -REFRIGERANT
The unit is equipped with high- - and low- -pressure switches. If the
control senses the opening of a high- - or low- -pressure switch, it
will respond as follows:
1. De- -energize the compressor contactor (HPS1 & LPS) or
the compressor solenoid contactor (HPS2).
2. Keep the outdoor fan operating for 15 minutes.
3. Display the appropriate fault codes.
4. After a 15 minute delay, if there is still a call for cooling
and the LPS or HPS is reset, the compressor contactor is
energized.
5. If LPS or HPS has not closed after a 15 minute delay, the
outdoor fan is turned off. If the open switch closes anytime
after the 15- -minute delay, then resume operation with a
call for cooling.
6. If LPS or HPS trips 3 consecutive cycles, the unit
operation is locked out for 4 hours.
7. In the event of a high- -pressure switch trip or high pressure
lockout, check the refrigerant charge, outdoor fan
operation and outdoor coil for airflow restrictions.
8. In the event of a low- -pressure switch trip or low pressure
lockout, check the refrigerant charge and indoor airflow.
CONTROL FAULT
If the HP/AC control board has failed, the control will flash the
appropriate fault code (See Table 5). The control board should
be replaced.
BROWN OUT PROTECTION
If the line voltage is less than 187v for at least 4 seconds, the
appropriate compressor contactor and fan relay are de- -energized.
Compressor and fan operation are not allowed until voltage is a
minimum of 190v. The control will flash the appropriate fault
code (See Table 5).
230V LINE (POWER DISCONNECT) DETECTION
If there is no 230v at the compressor contactor when the unit is
powered and cooling demand exists, the appropriate error code is
displayed. Verify that the disconnect is closed and 230v wiring is
connected to the unit.
COMPRESSOR VOLTAGE SENSING
The control board input terminals VS and L2 (See Fig. 17) are
used to detect compressor voltage status, and alert the user of
potential problems. The control continuously monitors the high
voltage on the run capacitor of the compressor motor. Voltage
should be present any time the compressor contactor is energized,
and voltage should not be present when the contactor is
de- -energized.
CONTACTOR SHORTED DETECTION
If there is compressor voltage sensed when there is no demand for
compressor operation, the contactor may be stuck closed or there
is a wiring error. The control will flash the appropriate fault code.
COMPRESSOR THERMAL CUTOUT
If the control senses the compressor voltage after start- -up, and is
then absent for 10 consecutive seconds while cooling demand
exists, the thermal protector is open. The control de- -energizes
the compressor contactor for 15 minutes, but continues to operate
the outdoor fan. The control Status LED will flash the
appropriate code shown in Table 5. After 15 minutes, with a call
for low or high stage cooling, the compressor contactor is
energized. If the thermal protector has not re- -set, the outdoor fan
is turned off. If the call for cooling continues, the control will
energize the compressor contactor every 15 minutes.
thermal protector closes (at the next 15 minute interval), check
the unit will resume operation.
If the thermal cutout trips for three consecutive cycles, then unit
operation is locked out for 4 hours and the appropriate fault code
is displayed.
NO 230V AT COMPRESSOR
If the compressor voltage is not sensed when the compressor
should be starting, the contactor may be stuck open or there is a
wiring error. The control will flash the appropriate fault code.
Check the contactor and control box wiring.
TROUBLESHOOTING UNIT FOR PROPER SWITCHING
BETWEEN LOW & HIGH STAGES
Check the suction pressures at the service valves.
pressure should be reduced by 3- -10% when switching from low
to high capacity.
NOTE: The liquid pressures are very similar between low and
high stage operation, so liquid pressure should not be used for
troubleshooting.
Compressor current should increase 20- -45% when switching
from low to high stage.
energized in high stage, should measure 24vac.
COMPRESSOR INTERNAL RELIEF
The compressor is protected by an internal pressure relief (IPR)
which relieves discharge gas into compressor shell when
differential between suction and discharge pressures exceeds 550
- - 625 psi. The compressor is also protected by an internal
overload attached to motor windings.
TEMPERATURE THERMISTORS
Thermistors are electronic devices which sense temperature. As
the temperature increases, the resistance decreases. Thermistors
are used to sense outdoor ambient (OAT) and coil temperature
(OCT). Refer to Fig. 24 for resistance values versus temperature.
See Fig. 25 for OCT location.
If the outdoor ambient or coil thermistor should fail, the HP/AC
control will flash the appropriate fault code (See Table 5).
IMPORTANT: Coil thermistor is factory mounted. Check to
insure thermistor is mounted properly. Outdoor air thermistor
(OAT) is field mounted and connected. Verify that the OAT has
been properly installed.
THERMISTOR CURVE
90
80
70
60
50
40
30
20
10
0
0 20 40
TEMPERATURE (DEG. F)
Fig. 24 - - Resistance Values Versus Temperature
30
If the
Suction
The compressor solenoid, when
60 80 100 120
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