Service Manual -
HRG18xxS1P
508206-01
Issue 2140
Page 25 of 83
Unit Operation
HRG18 Unit Operation with a Conventional
24VAC Non-Communicating 2-Stage Thermostat
When the HRG18 unit is installed with a conventional
24VAC non-communicating 2-stage thermostat, a Y1 first
stage heating or cooling demand will initiate heating or
cooling operation and first stage indoor blower operation.
The compressor will be controlled in the variable capacity
mode by varying the compressor capacity to obtain the
target suction pressure set point. The Y2 second stage
heating or cooling demand will initiate second stage
blower operation. Increased air volume will increase the
load on the indoor coil and increase the suction pressure.
The HRG18 compressor capacity will continue to be
controlled based upon the suction pressure. The unit
capacity will be controlled in the variable capacity mode
throughout the range of capacity from minimum capacity
to maximum capacity. If the Y2 demand remains after 20
minutes, the HRG18 control will begin to ramp up the
compressor capacity until maximum capacity is achieved.
The HRG18 unit will cycle off once the thermostat
demand is satisfied.
HRG18
Unit Operation with a Conventional
24VAC Non-Communicating Single-Stage
Thermostat
When the HRG18 unit is installed with a conventional
24VAC non-communicating single-stage thermostat, a Y1
first stage heating or cooling demand will initiate heating
or cooling operation and heating or cooling indoor blower
operation. In single stage thermostat applications, a
jumper must be installed between Y1 and Y2 on the
HRG18 outdoor control. The compressor will be
controlled in the variable capacity mode by varying the
compressor capacity to obtain the target suction pressure
set point. If the heating or cooling demand remains after
20 minutes, the HRG18 control will begin to ramp up the
compressor capacity until maximum capacity is achieved.
The HRG18 unit will cycle off once the thermostat
demand is satisfied.
Defrost Function
The outdoor unit control uses a time-dependent frost
accumulation duration demand defrost control algorithm
to provide a demand defrost when the system falls below
optimum levels. The demand defrost control algorithm
is reactive based upon the previous heat pump run time
between defrost cycles (frost accumulation time) and the
Heating Operation Mode Jumper
The Heating Operation Mode Jumper is only used on
applications installed with a conventional 24VAC non-
communicating heat pump thermostat. In applications
with a conventional 24VAC non-communicating heat
pump thermostat, the compressor capacity is controlled to
maintain the target liquid pressure setpoint. The Heating
Operation Mode Jumper has two selectable heating
modes. The two modes are Efficiency (Jumper installed
on Pins 1 & 2) and Comfort Mode (Jumper Removed).
The factory default position is the Efficiency Mode. The
Efficiency mode has a variable liquid pressure setpoint
that will vary with the outdoor temperature; as the outdoor
temperature decreases, the liquid pressure setpoint will
increase. When the Operation Mode jumper is installed
in the “Comfort Mode” the liquid pressure setpoint is 425
psig.
Operation Mode
Jumper
Jumper
Position
Target Liquid Pressure
Setting
Efficiency (default) Pin 4 to Pin 5
Variable based on OAT
Comfort
Jumper Off
425 PSIG
Table 10. Heating Operation Mode Jumper
(Conventional 24VAC Thermostats Only)
Figure 15. Operation Mode Jumper