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Heating or
Cooling Control
Mode Operation
Heating or Cooling
Operation
For both single and dual compressor
operation, the ZN510 controller
cycles the compressor(s) on and off
to meet heating or cooling zone
demands. The controller uses the
unit capacity and pulse width
modulation (PWM) logic along with
minimum on/off timers to determine
the operation for compressor 1.
With a dual compressor unit, if the
desired conditions are not met by
controlling only the first
compressor, the controller runs
compressor 1 continuously and
controls compressor 2 according to
PWM logic along with the minimum
on/off timers. See Table 6 for heat
pump heating or cooling operation.
Certain heat pump configurations
may use one or two compressors for
cooling control. Heat pumps use
reversing valve control to switch
between heating and cooling. The
controller supports cooling only
configurations and heat pump
configurations.
For heat pump configurations, the
unit’s reversing valve is energized in
cooling and de-energized in heating.
For cooling, the reversing valve
output is energized simultaneously
with the compressor (compressor 1
in two compressor applications).
The reversing valve remains
energized until the controller turns
on the compressor for heating,
simultaneously de-energizing the
reversing valve. The reversing valve
only changes state when the
controller turns on compressor 1.
When a power failure occurs, the
reversing valve output defaults to
the heating (de-energized) state. To
reduce noise due to refrigeration
migration after compressor
shutdown, the controller does not
immediately operate the reversing
valve. The reversing valve changes
state only when the compressor
controls on, except when the
controller is in off mode.
For cooling only configurations, no
reversing valve is present and the
controller uses the compressor
stages for cooling.
Compressor Minimum
ON/OFF Timers
z When fan mode = OFF, Com-
pressor minimum
ON timers are
ignored.
z When fan mode = AUTO, Com-
pressor minimum
OFF timers are
observed.
z The diagnostic reset ignores the
compressor timers
ON and OFF.
z A communicated compressor
disabled or unoccupied signal
ignores minimum
ON times.
Table 7: Heat pump heating or cooling operation*
Unit
Capacity
0%
Between
0 and 50%
Between
50 and 100%
100%
Single compressor
Compressor
OFF
continuously.
Compressor output is controlled according to pulse width
modulation (PWM) logic between 0 and 100%. The
controller calculates the compressor on/off times based
on PWM logic and heating/cooling capacities. The
compressor is controlled on for longer periods as the
capacity increases and shorter periods as the capacity
decreases.
Compressor
ON
continuously.
Dual (Two) compressors
Both compressors
OFF continuously.
#1:
ON PWM.
#2:
OFF continuously.
#1:
ON continuously.
#2:
ON PWM.
Both compressors
ON
continuously.
*Note: No diagnostics present.