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HPXA16 SERIES
Time
If 6 hours of heating mode compressor run time
has elapsed since the last defrost cycle while the coil tem-
perature remains below 35°F (2°C), the demand defrost
control will initiate a defrost cycle.
Actuation
When the reversing valve is de−energized,
the Y1 circuit is energized, and the coil temperature is be-
low 35°F (2°C), the board logs the compressor run time. If
the board is not calibrated, a defrost cycle will be initiated
after 34 minutes of heating mode compressor run time.
The control will attempt to self−calibrate after this (and all
other) defrost cycle(s).
Calibration success depends on stable system tempera-
tures during the 20−minute calibration period. If the board
fails to calibrate, another defrost cycle will be initiated after
90 minutes of heating mode compressor run time. Once
the defrost board is calibrated, it initiates a demand defrost
cycle when the difference between the clear coil and
frosted coil temperatures exceeds the maximum differ-
ence allowed by the control OR after 6 hours of heating
mode compressor run time has been logged since the last
defrost cycle.
Termination
The defrost cycle ends when the coil tem-
perature exceeds the termination temperature or after 14
minutes of defrost operation. If the defrost is terminated by
the 14−minute timer, another defrost cycle will be initiated
after 34 minutes of run time.
Test Mode
[NOTE − Coil sensor temperature must be
below 35ºF before the defrost board will initiate a
test" defrost.]
When Y1 is energized and 24V power is
being applied to the board, a test cycle can be initiated by
placing the termination temperature jumper across the
Test" pins for 2 to 5 seconds. If the jumper remains across
the Test" pins longer than 5 seconds, the control will ig-
nore the test pins and revert to normal operation. The
jumper will initiate one cycle per test.
Enter the TEST" mode by placing a shunt (jumper) across
the TEST" pins on the board
after
power−up. (The TEST"
pins are ignored and the test function is locked out if the
shunt is applied on the TEST" pins before power−up).
Board timings are reduced, the low−pressure switch is ig-
nored and the board will clear any active lockout condition.
Each test pin shorting will result in one test event.
For
each TEST" the shunt (jumper) must be removed for at
least 1 second and reapplied. Refer to flow chart (figure
22) for TEST" operation.
Note: The Y1 input must be active (ON) and the O" room
thermostat terminal into board must be inactive.
Defrost Board Diagnostics
See table 10 to determine defrost board operational condi-
tions and to diagnose cause and solution to problems.
If in
COOLING
Mode
If in
HEATING
Mode
If in
DEFROST
Mode
Short test pins for longer
than 1
second but less
than 2.0 seconds
Short test pins for
more than 2.0 seconds
Y1 Active (0" line inactive)
Figure 22
Test Mode
Test pin short REMAINS in place for more than 5 seconds
Test pins short REMOVED before a
maximum of 5 seconds
Clear any short cycle lockout
and/or 5−strike fault lockout
function, if applicable. No
other functions will be
executed and unit will
continue in the mode it was
operating.
No further test mode
operation will be
executed until the test
short is removed and
reapplied.
The controller will check for
ambient and coil faults (open or
shorted). If a fault exists, the unit
will remain in Heat Mode and no
further test mode operation will
be executed until the test short
is removed and re applied. If
no fault exists and ambient
temperature is below 35ºF, the
unit will go into Defrost mode.
The unit will terminate
defrost and enter Heat
Mode uncalibrated with
defrost timer set for 34
minute test. No further
test mode operation will
be executed until the test
short is removed and
reapplied.
Clear any short cycle lockout or 5−strike fault
lockout function, if applicable.
The unit will return to Heat mode uncalibrated with defrost
timer set for 34 minutes. No further test mode operation will
be executed until the test short is removed and re applied.
The unit will remain in Defrost mode
until termination on time or temperature
