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Heat Pump Operation
When an AZ6500 Zoneline is in the heating mode,
the resistance heater or the compressor runs with
the appropriate fans. The control is capable of
independently switching power for two resistance
heater loads. Each of the two heater loads can
be made up of different heating elements, but the
elements will be tied together in parallel. There
are three stages of operation associated with the
heating mode:
• Stage 1: Heating due to heat pump
(compressor) with both fans on.
• Stage 2: Heating due to heat pump
(compressor) and supplemental 1,000-watt
resistance heater (Heater A) with both fans
on. (this mode can also be activated via the
Auxiliary Set (or Aux Set) mode to run in place
of stage 1 heating). This auxiliary setting
is known as Boost Heat, and essentially
disables Stage 1 heating which is replaced by
Stage 2 heating. When this mode is active, it
will run when the Zoneline is being controlled
via the Zoneline control panel or when a
remote wall thermostat is connected and
calling for heat pump. It will override Stage
1 heating in both cases. NOTE: Any time
the Zoneline enters Stage 2 heating mode, it
should continue heating in this mode until the
room temperature is satisfied. If the room
offset increases, then Stage 3 heating will be
engaged.
• Stage 3: Heating due to resistance heater
(Heater A, B and C); indoor fan only on.
NOTE: Any time the Zoneline enters Stage 3
heating mode, it will continue heating in this
mode until the room temperature is satisfied,
regardless of indoor room temperature offset or
outdoor temperature conditions. The Zoneline
can then resume normal heating operation
modes of Stage 1 or Stage 2 heating upon the
next call for heat.
NOTE: In low fan speed, the Zoneline will only
activate heater A and B to allow for a maximum
heater output of 3,800 watts. A, B, and C output
is only available in high speed. Heat Pump
Mode and Heater B will never be on at the
same time.
Upon initial start-up or resumption after a power
interruption, Stage 3 (Heater A and Heater B) are
energized at full power to generate heat until the
room temperature rises to the temperature setting
regardless of the outdoor temperature.
Automatic changeover between the compressor
and the heating elements is utilized.
In order to keep the compressor from stalling
out when trying to start against the high side
refrigerant pressure, the control circuit has a
built-in automatic time delay to allow the internal
pressure to equalize. The control circuit will not
try to start the compressor until it has been off
for 3 minutes. To minimize compressor cycling,
the control has a built-in minimum compressor
run time of 3 minutes (+/- 10 seconds). Even
if the thermostat is satisfied, or the indoor
temperature is dropping, the compressor will run
for a minimum of 3 minutes. The Zoneline can
switch to Stage 2 heating, but must wait until
the 3 minutes of compressor run time is satisfied
before switching to Stage 3 heating.
• FIRST STAGE HEAT (HEAT PUMP ONLY)
Once heating initializes, the room temperature
will start to rise. The compressor will run
until the temperature rises 0.9°F above the
temperature control setpoint, at which time
the compressor will shut down. If the outdoor
ambient temperature is less than 25°F, Stage
1 heating will be disabled and only Stage 3
heating will energize. This is also the case
for the remote wall thermostat. When the
outdoor ambient temperature is greater than
46°F, the Zoneline runs at First Stage (Heat
Pump).
• SECOND STAGE HEAT (HEAT PUMP +
HEAT A): Boost Heat mode
When either the room temperature falls
from the setting by greater than 1.8°F, or
the outdoor temperature is lower than 25°F,
Stage 2 heating will be disabled and only
Stage 3 heating will energize.
If the outdoor temperature is above 25°F the
control will energize Stage 2 heating. Stage 2
heating will continue to operate until the room
temperature exceeds the temperature control
setpoint by 0.9°F, at which time the heater
and compressor will stop.
– 10 –
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