Carrier Residential Air Conditioners and Heat Pumps Application Manualline page 51

230v Brown- -Out Protection Defeated
The brownout feature can be defeated if needed for severe noisy
power conditions. This defeat should always be a last resort to
solving the problem. Defeat is available on the User Interface
setup screen (available with SYSTXBBUID01- -C UI) or can be
initiated through the forced defrost pins for non- -communicating
systems as follows:
The brownout toggle is accomplished by shorting the defrost pins
from power up with the OAT and OCT sensor connector removed.
After 3 seconds, the status of the force defrost short and the
OAT/OCT as open will be checked. If correct, then the brownout
will be toggled.
S Status code 6 shows the brownout is disabled.
S Status code 5 shows the brownout is active.
After the brownout defeat is set, power down and reinstall the
OAT/OCT sensor and remove the short from the forced defrost
pins. As long as the short on the forced defrost remains, the OAT
and OCT faults will not be cleared. The code will continue to be
flashed.
The control is shipped with the brownout active. The change in
status is remembered until toggled to a new status. A power
down/power up sequence will not reset the status. It may be
necessary to do the toggle twice to cycle to the desired state of the
defeat.
230V Line (Power Disconnect) Detection
If there is no 230v at the compressor contactor(s) when the indoor
unit is powered and cooling or heating demand exists, the
appropriate fault code is displayed. Verify the disconnect is closed
and 230v wiring is connected to the unit.
Compressor Voltage Sensing
The control board input terminals labeled VS, and L2 on
25HNB6/24ANB7 and 25HNB9/24ANB1 models (see Fig. 33)
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
may be a wiring error. The control will flash the appropriate fault
code.
Compressor Thermal Cutout - -
24ANB1/24ANB7/25HNB6/25HNB9
If the control senses the compressor voltage after start- -up and is
then absent for 10 consecutive seconds while cooling or heating
demand exists, the thermal protector is open.
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 16. After 15 minutes,
with a call for low or high stage cooling or heating, the compressor
contactor is energized. If the thermal protector has not re- -set, the
outdoor fan is turned off. If the call for cooling or heating
continues, the control will energize the compressor contactor every
15 minutes. If the 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.
Low or High Contactor Open / No 230V at
Compressor Contractor
24ANB1/24ANB7/25HNB6/25HNB9
If the compressor voltage is not sensed when the compressor
should be starting, the appropriate 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 units for proper switching
between low & high stages - -
24ANB1/24ANB7/25HNB6/25HNB9
Check the suction pressures at the service valves. Suction 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.
high stage, should measure 24vac.
When the compressor is operating in low stage the 24v DC
compressor solenoid coil is de- -energized. When the compressor is
operating in high stage, the 24v DC solenoid coil is energized. The
solenoid plug harness that is connected to the compressor HAS an
internal rectifier that converts the 24v AC signal to 24v DC. DO
NOT INSTALL A PLUG WITHOUT AN INTERNAL
RECTIFIER.
Unloader Test Procedure - -
24ANB1/24ANB7/25HNB6/25HNB9
The unloader is the compressor internal mechanism, controlled by
the DC solenoid, that modulates between high and low stage. If it
is suspected that the unloader is not working, the following
methods may be used to verify operation.
1. Operate the system and measure compressor amperage.
Cycle the unloader on and off at 30 second plus intervals at
the UI (from low to high stage and back to low stage). Wait
5 seconds after staging to high before taking a reading. The
compressor amperage should go up or down at least 20
percent.
2. If the expected result is not achieved, remove the solenoid
plug from the compressor and with the unit running and the
UI calling for high stage, test the voltage output at the plug
with a DC voltmeter. The reading should be 24 volts DC.
3. If the correct DC voltage is at the control circuit molded
plug, measure the compressor unloader coil resistance. The
resistance should be approximately 330 or 1640 ohms de-
pending on unloader coil supplier. If the coil resistance is
infinite or is grounded, the compressor must be replaced.
The control
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The compressor solenoid when energized in