Unit Operation - GE NS18HMA Installation Instructions Manual

Heating Operation Mode Jumper
The Heating Operation Mode Jumper is only used on
applications installed with a conventional 24VAC heat
pump thermostat. In applications with a conventional
24VAC 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
Efficiency (default) Pin 4 to Pin 5
Comfort Jumper Off
Table 10. Heating Operation Mode Jumper
(Conventional 24VAC Thermostats Only)
Figure 12. Operation Mode Jumper
508133G01 / 31-5000715
Target Liquid Pressure
Setting
Variable based on OAT
425 PSIG
Issue 2140

Unit Operation

NS18HMA Unit Operation with a Conventional
24VAC 2-Stage Thermostat
When the NS18HMA unit is installed with a conventional
24VAC 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 NS18HMA 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 NS18HMA
control will begin to ramp up the compressor capacity until
maximum capacity is achieved. The NS18HMA unit will
cycle off once the thermostat demand is satisfied.
NS18HMA Unit Operation with a Conventional
24VAC Single-Stage Thermostat
When the NS18HMA unit is installed with a conventional
24VAC 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 NS18HMA 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 NS18HMA control
will begin to ramp up the compressor capacity until
maximum capacity is achieved. The NS18HMA unit will
cycle off once the thermostat demand is satisfied.
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