Carrier 25HNA Infinity
Series Installation Instructions Manual page 15

Compressor Voltage Sensing
The control board input terminals labeled VS, VR and L2 on
25HNA6 models and VS and L2 on 25HNA9 models (see Fig. 9)
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.
25HNA6 Models − Compressor Thermal Cutout
The control senses the compressor voltage at VR and VS. When
starting or running, a phase difference of the voltages on the
inputs will indicate the thermal protector is closed. If the phase
difference is 5_ or less for 10 seconds, the internal protector is
open. The control de−energizes the appropriate compressor
contactor for 15 minutes, but continues to operate the outdoor
fan. The control Status LED will flash the appropriate code
shown in Table 7. After 15 minutes, with a call for low or high
stage cooling or heating, the appropriate 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.
25HNA9 Compressor Thermal Cutout
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 7. 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 (25HNA6 models) / No 230V at
Compressor Contractor (25HNA9 models)
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.
25HNA6 Models Only − Compressor Start Detection on
Models with Bristol Compressors Only
In low stage, if the specified start voltage at VR terminal is not
achieved, the start relay is de−energized after 1 second and the
control will flash the appropriate fault code.
In high stage, if the specified start voltage at VS terminal is not
achieved, the start relay is de−energized after 1 second and the
control will flash the appropriate fault code.
If the specified start voltage is not achieved for 3 consecutive low
stage starts, low stage operation is locked out for 30 minutes. If
the specified start voltage is not achieved for 3 consecutive high
stage starts, high stage operation is locked out for 30 minutes.
The control will flash the appropriate fault code.
Troubleshooting 25HNA6 units for proper switching between
low & high stages
Check the suction and liquid pressures at the service valves.
Suction pressure should be reduced by 5−10% when switching
from low to high capacity. There should be a 10−20% increase in
liquid pressure when switching from low to high capacity.
Compressor current should increase 100−250% when switching
from low to high stage.
Troubleshooting 25HNA9 units 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.
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 DC signal to 24v
AC. DO NOT INSTALL A PLUG WITHOUT AN
INTERNAL RECTIFIER.
Unloader Test Procedure
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
The control
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 4 to 18
volts.
3. If the correct DC voltage is at the control circuit molded
plug, measure the compressor unloader coil resistance.
The resistance should be 32 to 60 ohms depending on
compressor temperature. If the coil resistance is infinity,
much lower than 32 ohms, or is grounded, the compressor
must be replaced.
Temperature Thermistors
Thermistors are electronic devices which sense temperature. As
the temperature increases, the resistance decreases. Thermistors
are used to sense outdoor air (OAT) and coil temperature (OCT).
Refer to Fig. 12 for resistance values versus temperature.
If the outdoor air or coil thermistor should fail, the control will
flash the appropriate fault code. (See Table 7.)
IMPORTANT: The outdoor air thermistor and coil thermistor
should be factory mounted in the final locations. Check to
ensure thermistors are mounted properly per Fig. 10 and Fig.
11.
15
Suction
The compressor solenoid when