Trane Tracer User Manual

18

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.

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*

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.