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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 satised.  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 satised, 
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 satised, 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 satised 
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.
  Heat Pump Operation