035-20401-001 Rev. A (0904)
Unitary Products Group
9
LED DIAGNOSTIC INDICATORS
The control includes two LED’s that display various types of diagnostic
information. LED1 is red and LED2 is green. The location of the LED’s
is shown in Figures 11 & 14. These LED’s are used to display opera-
tional mode, status, and fault information.
OPERATIONAL MODE DETECTION
The control can be used in a variety of applications including heat
pumps and air conditioners with modulating compressors. The control
uses various inputs to determine the proper mode of operation.
It looks for the presence of a reversing valve connected to the RV and
RVG terminals to determine if it should operate as a heat pump or an air
conditioner. If the reversing valve is not connected, the control will not
operate in the heat pump mode. The control senses the reversing valve
loads and determines the operational mode each time power to the
control is cycled.
The control also senses the connections that are made to the M, M1,
and M2 terminals and determines the correct operational mode for the
control. This is done each time power to the control is cycled. There-
fore, it is important for this 2-stage system that no loads be attached to
the M1 terminal of the control. Incorrect system behavior could result.
IMPORTANT: Do not connect any loads to the M1 terminal of the
control. Incorrect system behavior could result.
OPERATIONAL MODE DISPLAY
The control will display its active operational mode using the onboard
LED’s when the TEST pins are connected while no thermostat signals
are energized. See Table 2. The control will display the operational
mode as long as the TEST pins are shorted and no thermostat signals
are energized. When the TEST pin short is removed, the control will
return to normal LED displays. The X/L output will be energized (with
the number of flashes corresponding to the active defrost curve) while
the operational mode is displayed. For example, if defrost curve 2 is
active, the X/L output will be energized with two flashes while the oper-
ational mode is being displayed on the LED’s.
If the control displays an operational mode other than LED2 (Green)
ON and LED1 (Red) 3 flash indicating a heat pump with a scroll 2-stage
compressor, an error condition exists. Check all wiring of the reversing
valve (RV and RVG terminals) and compressor outputs (M, M1, and M2
terminals). Cycle 24 VAC power to the control and check the opera-
tional mode again.
STATUS MODE DISPLAY
The control also provides status codes using the LED’s. Status codes
indicate the state of operation of the unit but do not represent a fault.
Table 3 describes the LED displays during status codes. Status codes
will not be displayed when a fault code is present.
During the following conditions, the control will not energize the X/L out-
put.
FAULT CODE DISPLAY
X/L Output
The X/L terminal of the heat pump control is typically connected to the
X/L input of the room thermostat. The thermostat uses this signal to
notify the homeowner of a problem with the heat pump using an LED or
LCD display. When the control energizes the X/L terminal, the thermo-
stat displays the flash code so the homeowner can see it.
The heat pump control informs the homeowner of the type of condition
that is present using flash codes. Table 4 shows the condition catego-
ries and the corresponding X/L flash codes.
The control will continue to energize the X/L output for fault codes hav-
ing an X/L code of 4 flashes even after the thermostat calls are
removed. The control does this to notify the installer or homeowner that
a significant problem with the wiring or system configuration is present
and needs to be corrected.
The control will continue to energize the X/L output until the condition
that caused the fault condition no longer exists.
LED Display
The control will display any fault code that is currently active using the
LED’s. The control will display the fault code, pause two seconds, and
display the fault again. The control will continue the fault code display
until the condition that caused the fault code no longer exists. If multiple
fault codes are present at the same time, the control will display only
the most recent fault. The other active errors may be accessed from
memory using the LAST ERROR pushbutton.
Operational Fault Codes
Table 5 shows the operational faults that the control can detect. The
control displays this type of error by flashing LED1 (Red) only. LED1
(Green) is not energized. These faults typically occur when the heat
pump has been operating and a problem occurs.
TABLE 2:
Operational Mode Display
Operational Mode
LED1
(Red)
LED2
(Green)
Heat Pump
ON
Air Conditioner
OFF
Single-Stage Compressor
1
Reciprocating Two-Stage Compressor
2
Scroll Two-Stage Compressor
3
TABLE 3:
Status Code Display
Description
LED1
(Red)
LED2
(Green)
No power to control
OFF
OFF
First-stage compressor operation – not
applicable to single stage compressor
OFF
ON
Second-stage or full capacity compressor
operation
ON
ON
Control normal operation – no
call for compressor
OFF
2 sec ON
2 sec OFF
Control normal operation – call for com-
pressor and ASCD timer (5 min.) is active
OFF
Rapid
Flash
No fault codes in memory – Initiated
by LAST ERROR pushbutton
2
2
Fault code memory cleared – Initiated
by LAST ERROR pushbutton
3
3
TABLE 4:
X/L Output Categories
Condition Category
X/L
Soft Lockout – Reset with interruption of thermostat
call following correction of fault condition
2 flashes
Hard Lockout – Reset by cycling power
to system
3 flashes
Wiring, sensor or control setting related error
4 flashes
