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also have anti-short cycle protection built in causing a
delay in one or both stages. A protective timer circuit
could hold the compressor(s) off for up to five minutes
following a previous operation or an interruption of the
main power. Consult the operation manual for the type
thermostat being installed.
2. Verify the air being discharged at the registers is warmer
than room temperature.
3. After allowing the unit to operate for several minutes,
set the thermostat temperature switch below room
temperature, verify that fans, blower, and compressors
cycle off with the thermostat.
NOTE: If electric heat has been added, Stage 2
compressor will cycle off while Stage 3 heater elements
are energized.
Field Installed Electric Heat (Optional)
This package heat pump system is designed to allow
optional electric heat to be field installed as required by
the building's particular heating load, as make up heat
during defrost mode, and as Emergency Heat. NOTE: If
optional electric heat is added, a 3 Stage Heat / 2 Stage
Cool 24VAC heat pump thermostat must be used.
9, 18, 30, and 35 KW models are available for all unit
models. Use only NORDYNE manufactured H5HK series
heater kits with these units.
Install the heater kits as directed by the instruction sheet
that comes as part of the heater kit. Follow all cautions
and warnings as directed.
1. Set the thermostat to above room temperature.
2. Verify that Stage 1 compressor outdoor fan motors and
blower are energized and the electric heat is energized.
3. After the unit has run for approximately five minutes,
set the thermostat below room temperature and verify
that the electric heat, Stage 1 compressor, fans, and
blower have de-energized.
Emergency Heat
Most Heat Pump thermostats will include a system
switch position termed EM.HT. or AUX.HT, etc. This is
a back-up heating mode to be used only if a problem is
suspected. With the system switch set to Emer. Ht., etc.,
the compressor(s) and outdoor fans will be locked off
and supplemental heat (electric resistance heating) will
be used as a source of heat. Sustained use of electric
resistance heat in place of the heat pump will result in an
increase in electric utility costs.
Defrost Mode
During cold weather heating operation, the outdoor unit
will develop a coating of snow and ice on the outdoor
section heat transfer coils. This is normal and the unit will
defrost itself automatically. During the defrost cycle, the
outdoor fans will stop while the compressor(s) continue
to operate and heat the outdoor coil, causing the snow
and ice to melt. During defrost, some steam may rise
from the outdoor unit as the warm coil causes the melted
frost to evaporate.
Verify Operation of Over-Temperature Limit
Control
WARNING:
Uninsulated live components are exposed when
element access panel is removed.
Make sure all access panels are in place and that there
is power to the unit. Block the return airflow to the unit
by installing a close-off plate in place of or upstream of
the filter. Set the thermostat above room temperature
and verify the unit operates with the correct operating
sequence. The over-temperature limit control should turn
off the electric strip heat within approximately four minutes.
NOTE: The exact time depends on the efficiency of the
close-off in the return air to the unit.
The circulating air blower should continue to run when
the over-temperature limit control switch opens. Remove
the close-off immediately after the over-temperature limit
control opens. If the unit operates for more than four
minutes with no return air, set the thermostat below room
temperature, shut off the power to the unit, and replace
the over-temperature limit control.
OPERATING SEQUENCE
The operating sequences for the heating, cooling, and
fan modes are described below. Refer to
19)
&
Figure 12 (page 20)
Heat Pump Cooling Mode
1. Set the thermostat system switch to Cool and the
thermostat fan switch to Auto.
NOTE: Heat pump thermostats typically energize
reversing valves through the O terminal with the
system switch set to Cool. Reversing valves will remain
energized until the system switch is moved to Off, Heat,
or Emer.Heat. Consult the instructions for the specific
type of thermostat being used for proper unit operation.
2. On a call for cooling the thermostat closes, applying
24 VAC directly to Y1, G, and Y2 if Stage 2 cooling is
required. NOTE: Stage 1 Compressor (Y1) has a built in
5 minute anti-short cycle timer (ASCT) function built into
the defrost board. Any loss of power or 24V interruption
to the defrost board will cause the ASCT to reset and
start the timing cycle over.
3. G applies 24VAC to the main circulating blower circuit.
4. Y1 & Y2 apply 24VAC through all safety switches before
energizing their respective compressor contactors.
5. Outdoor fan contactor is energized through auxiliary
contacts on either of the compressor contactors once
energized.
6. As the thermostat is satisfied the contactors are de-
energized in sequence.
7. The circulating blower motor is de-energized immediately.
Figure 11 (page
for the unit.
11
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