12
Demand Defrost control
The demand defrost board controls the defrost cycle
in response to ambient temperature, outdoor coil
temperature and accumulated compressor run time. The
heat pump is allowed to operate in the heating mode
until the combination of outdoor ambient and outdoor
coil temperatures indicate that defrosting is necessary,
based on the programmed defrost curve. There are four
preprogrammed defrost curves on the board.
• A jumper pin is used to switch between the different
curves. The default jumper position is curve 1 and is the
recommended setting for most standard applications.
See
Table 4
for additional defrost curves settings.
• The factory default setting does not include a 30 second
compressor delay function and has a 40° F defrost
terminate temperature. If additional defrost time is
needed, a higher terminate temperature is available
by selecting a different demand curve.
notE:
The 30
second compressor delay function is optional and based
on the demand curve selected.
• The standard defrost cycle will terminate after 13 minutes
and 39 seconds or when the coil temperature reaches
its terminate temperature, whichever occurs first.
• The defrost board is equipped with a 5 minute Anti-Short
Cycle Delay (ASCD). The compressor will not turn on
until it reaches the minimum 5 minute off time.
• The control contains a forced - defrost feature, which
places the system into defrost mode every 6 hours and
4 minutes, unless the coil temperature is above the
selected terminate temperature.
• The system can be manually forced into defrost mode at
any time by shorting the
tESt
terminals on the demand
defrost board together for more than 9 seconds. The
coil temperature sensor does not need to be cold when
the unit is forced into defrost. After the
tESt
input is
removed, the defrost mode will terminate in 13.7 minutes,
if the coil temperature is above the terminate set-point,
or when the
Y
input is removed, whichever occurs first.
notE:
If a demand curve is selected which has a 30
second compressor time delay in defrost, the delay is
reduced to 10 seconds in TEST mode.
optional Electric Heater kits
Optional electric heater kits are available in 9 kw and
15 kw heating capacities. Single package heat pumps
are designed to allow optional electric heat to be field
installed as required by the building’s particular heating
load. The options available for each unit are shown in the
heater kit installation instructions. As previously noted, a
field installed circuit breaker kit is available as a means
of electrical disconnect for the unit.
Install the heater kits as directed by the instructions
supplied with the heater kit. Follow all cautions and
warnings as directed.
table 3. thermostat Wire gauge
WirE
gaugE
rEcommEnDED maximum
WirE lEngtH (Ft) From unit
to tHErmoStat
22
45
20
70
18
115
16
180
table 4. Demand Defrost curve Profiles
jumPEr
PoSition
minimum timE
bEtWEEn
DEFroStS (min)
tErminatE
tEmPEraturE
(° F)
30 SEconD
comPrESSor
DElaY Function
1
20
40
no
2
20
40
YES
3
20
75
NO
4
20
75
YES
