035-20401-001 Rev. A (0904)
10
Unitary Products Group
Sensor or Switch Fault Codes
Table 6 shows the faults that the control can detect when a problem is
present with a sensor or switch. The control displays this type of error
by energizing LED1 (Red) constantly and flashing LED2 (Green).
These faults typically occur when the heat pump has been operating
and a problem occurs with a sensor or its wiring. These faults could also
occur during installation as the heat pump is configured.
Wiring Related Fault Codes
Table 7 shows the faults that the control can detect when a problem is
present with the system wiring or jumper configurations. The control
displays this type of error by flashing LED1 (Red) and energizing LED2
(Green) constantly. These faults typically occur when the heat pump is
first installed or when a system component such as the room thermostat
or indoor unit is replaced or rewired.
FAULT CODE MEMORY
Displaying Stored Fault Codes
The control will store up to five fault codes in memory. If more than five
faults occur, the five most recent fault codes will remain in memory. The
stored faults can be displayed by depressing the LAST ERROR push-
button for one to five seconds while no thermostat inputs to the control
are energized. See Figures 11 & 14 for the location of the pushbutton.
Since some room thermostats energize the O signal even when not
calling for compressor operation, turn the room thermostat to the SYS-
TEM OFF setting when displaying fault codes.
When the LAST ERROR pushbutton is depressed and released, the
control will display the stored fault codes beginning with the most
recent. The control will display the most recent fault code, pause two
seconds, and display the next fault code. The control will display the
stored error codes and then return to the normal LED status display
mode. The stored fault codes can be displayed again by depressing the
pushbutton again. When the control displays the fault codes with the
onboard LED’s, it will also energize the X/L output with the correspond-
ing flash code. The X/L output signal can be observed at the room ther-
mostat or at the control using a 24VAC LED test device connected to
the X/L terminal.
If the control has no fault codes stored in memory, it will flash both
LED’s twice simultaneously. If a thermostat signal is energized while the
control is displaying the stored error codes, the control will stop display-
ing the stored error codes and resume normal operation.
Clearing Fault Code Memory
Once the stored fault codes have been displayed and recorded, the
installer should clear the stored fault codes from the control’s memory.
This practice will enable better troubleshooting and diagnosis of system
problems. If the stored fault codes are not cleared after the cause of the
problem has been resolved, a service technician doing a later service
call may not know that the fault codes in the memory were caused by a
problem that has already been fixed. The technician may waste time
trying to fix a condition that no longer exists. Therefore, it is very impor-
tant to always clear the fault code memory after the unit is installed and
running properly following a service call.
IMPORTANT: Always clear the fault code memory after resolving
the condition that caused the fault code.
To clear the fault code memory, depress the LAST ERROR pushbutton
for longer than 5 seconds. The control will flash both LED’s three times
to indicate that the memory has been cleared. To confirm that the mem-
ory has been cleared, depress the LAST ERROR pushbutton for one to
five seconds. The control will flash both LED’s twice to indicate that no
faults are stored in memory.
TABLE 5:
Operational Fault Codes
Description
LED1
(Red)
LED2
(Green)
X/L
Operational Faults
Control Failure that still allows fault
code output
ON
OFF
4 if possible
High-pressure switch fault
(not in lockout yet)
1
OFF
OFF
High-pressure switch lockout
(last mode of operation was heat pump)
2
OFF
2 (soft)
3 (hard)
High-pressure switch lockout
(last mode of operation was defrost)
3
OFF
2 (soft)
3 (hard)
Low-pressure switch lockout
4
OFF
2 (soft)
3 (hard)
Low Voltage (< 19 VAC) preventing
further relay outputs
5
OFF
OFF
Low Voltage (< 16 VAC) stopped
current relay outputs
6
OFF
OFF
Pipe Freeze Protection
Timer expiration
7
OFF
4
TABLE 6:
Sensor or Switch Fault Codes
Description
LED1
(Red)
LED2
(Green)
X/L
Required Sensor or Switch Faults
Outdoor ambient sensor failure (short)
ON
1
2 (soft)
Outdoor ambient sensor failure (open)
ON
2
2 (soft)
Liquid line sensor failure (short)
ON
3
2 (soft)
Liquid line sensor failure (open)
ON
4
2 (soft)
Optional Discharge Line Sensor Faults
High discharge line temperature
ON
5
2 (soft)
3 (hard)
Low discharge line temperature
ON
6
2 (soft)
3 (hard)
Discharge line sensor failure (short)
ON
7
2 (soft)
Optional Bonnet Sensor Faults
Bonnet sensor failure (short)
ON
8
4
Fossil Fuel Mode setting error (FFUEL jumper
in OFF position but bonnet sensor present)
ON
9
4
TABLE 7:
Wiring Related Fault Codes
Description
LED1
(Red)
LED2
(Green)
X/L
Wiring Related Faults
Compressor Contactor Miswire
1
ON
4
Y2 present without Y1
2
ON
4
Y1 and W present without Y2 in
two stage mode
3
ON
4
O signal received in AC mode
4
ON
4
W signal received in AC mode
5
ON
4
W and O signal received in AC mode
6
ON
4
W and O signal received in HP mode
7
ON
4
Defrost Curve Jumper Error (Invalid jumper
setting preventing compressor operation)
8
ON
4
