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DISPlaY
C1
C2
Cooling, Stage One Call, Intermediate
C3
Cooling, Stage One Call, Low High
C4
Cooling, Stage Two Call, Nominal High
C5
H1
H2
Heating, Stage One Call, Intermediate
H3
Heating, Stage One Call, LowHigh
H4
Heating, Stage Two Call, Nominal High
H5
0L
_
0F
Table 5. Interface Board operating codes
For example, with a first stage call in cooling, if the setpoint
was satisfied quickly, the unit will restart the next time at a
lower speed. At a low or intermediate speed, if the setpoint is
not satisfied within 45 minutes, the speed will be increased.
If the unit cycles off after having a speed increase, the entire
next cycle will be at the higher speed. Also, the outdoor fan
will run for an extra minute after the compressor shuts off.
The actual current operating compressor speed can be
determined by checking the 2-character display on the interface
board. Refer to Figure 7 (page 12) and Table 5 (page 7).
Control operation is protected under U.S. patent number
US 8,011,199 B1
Blower Flow rates
Depending on the indoor equipment installed, blower air flow
may be adjustable. When paired with a matching model air
handler or gas furnace, the airflow is set by DIP switches on
the blower control board, providing one flow for second stage
compressor speeds and a lower flow for first stage compressor
speeds. Refer to the indoor equipment manuals for instructions
on how to select the desired air flows. High stage airflows used
for equipment ratings are as follows:
• 2 ton - 800 cfm
• 3 ton - 1200 cfm
•
4 ton - 1350 cfm
•
5 ton - 1500 cfm
Refer to indoor equipment installation instructions for options,
operation, and field wiring relating to dehumidification and
humidification.
Delay override
When performing startup tests or troubleshooting, the 5 minute
startup delay can be skipped by shorting the two J4 Test pins
indicated in Figure 7 for about 1 second while the compressor
is off and waiting to start. noTE: This will also clear the faults
stored in memory.
caPacITY STaGE
Cooling, Stage One Call, Low
Cooling, Stage Two Call, Boost
Heating, Stage One Call, Low
Heating, Stage Two Call, Boost
Startup Delay (5 minutes)
System Powered but Idle
In Defrost
Defrost cycle
This equipment features an adaptive demand defrost in heating
mode, which is enabled when the outdoor coil temperature
is below 35° F. After approximately 35 minutes of operating
in this condition for the first time, a defrost will be forced to
check the difference between the coil temperature and outdoor
air temperature, with the coil unfrosted. Subsequent defrosts
will be triggered when this temperature difference increases
(coil temperature drops) by an additional 6° F, referenced to
the outdoor ambient at that time. If this has not occurred by 6
hours of operation (with the coil below 35°), a defrost will be
run regardless. Following each defrost sequence, the unfrosted
air-to-coil temperature difference is rechecked, and that value
is used to determine the next defrost trigger temperature. In
this way the effect of frosting up is always compared to the
unfrosted performance of the coil in its current condition.
During every defrost cycle the compressor first shuts off, the
reversing valve shifts, the cycle reverses to heat up the outdoor
coil until the coil reaches the defrost termination temperature
setting (70° F by default), then the compressor shuts off again
for the reversing valve to shift back to the heating mode. During
the following 8 minutes (approximately) the unit will heat at
nominal speed to perform the coil differential temperature
check described above, after which the system will return to
normal heating capacity control.
If a defrost termination temperature setting other than 70° is
desired, it can be adjusted between 50° F and 80° F by placing
a jumper between pairs of pins on J1 near the lower right side
of the interface board inside the control panel (Figure 7). A
jumper is not required, however.
The defrost cycle may be artificially triggered for service and
troubleshooting purposes. With the unit running in heating
mode, simply short together the two J4 Test pins shown in
Figure 7 for about 1 second. noTE: This will also clear the
faults stored in memory. The 2-character display will show
"0F" when the defrost cycle is under way.
auxiliary Heat
During the coil heating phase of each defrost cycle, the 18
SEER iQ heat pump will call for auxiliary heat (electric strip
heat or gas furnace). Depending upon the features and
functionality of the installed thermostat, auxiliary heat may
also be turned on in the case of a faulted heat pump, if the
heat pump cannot satisfy heating demand, or if outdoor air
temperature is below a "balance point" setting.
Diagnostic Display
The interface board located inside the control panel has a
two character display which provides information regarding
operational status and fault history. When 24 vac control power
is provided to the board, the display will show some combination
of characters. In order to diagnose a problem with the unit, or
to determine its operational status, remove the control panel
cover, then observe the 2-character lighted display on the
interface board. Refer to Tables 5 (page 7) and 6 (page 8).
7
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