Page 20 of 26
508311G01 / 31-5000754
Issue 2250
Unit Operation
NS22HM Unit Operation with a Conventional
24VAC 2-Stage Heat Pump Thermostat
When the NS22HM 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 NS22HM 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 NS22HM control will
begin to ramp up the compressor capacity until maximum
capacity is achieved. The NS22HM
unit will cycle off once
the thermostat demand is satisfied.
NS22HM Unit Operation with a Conventional
24VAC Single-Stage Heat Pump Thermostat
When the NS22HM 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 NS22HM 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 NS22HM control will
begin to ramp up the compressor capacity until maximum
capacity is achieved. The NS22HM
unit will cycle off once
the thermostat demand is satisfied.
Start-Up
If unit is equipped with a crankcase heater, it should
be energized 24 hours before unit start-up to prevent
compressor damage as a result of slugging.
CAUTION
1. Rotate fan to check for frozen bearings or binding.
2.
Inspect all factory and field-installed wiring for loose
connections.
3. After evacuation is complete, open liquid line and
suction line service valves to release refrigerant
charge (contained in outdoor unit) into system.
4.
Replace the stem caps and secure finger tight, then
tighten an additional 1/6 of a turn.
5. Check voltage supply at the disconnect switch. The
voltage must be within the range listed on the unit
nameplate. If not, do not start equipment until the
power company has been consulted and the voltage
condition corrected.
6. Set thermostat for cooling demand, turn on power to
indoor blower, and close the outdoor unit disconnect
switch to start the unit.
7. Recheck unit voltage with unit running. Power must be
within range shown on unit nameplate.
Refrigerant Charging
Excessive amounts of liquid refrigerant entering the
suction line can damage the compressor. When adding
refrigerant, precautions must be taken to control the
flow of liquid into the system. This can be done by using
a liquid vaporizing adapter or manual control using a
sight glass as indicator.
CAUTION
Units are factory charged with the amount of R-410A
refrigerant indicated on the unit rating plate. This charge is
based on a matching indoor coil and outdoor coil with 15’
line set. For varying lengths of line set, refer to Table 10 for
refrigerant charge adjustment. A blank space is provided
on the unit rating plate to list the actual field charge.
Table 10. Refrigerant Charge Adjustment
Liquid Line Set Diameter
Oz. Per 5 ft. adjust from 15
ft. line set*
3/8 in.
3 oz. per 5 ft.
or 0.6 oz. per 1 ft.
* If line length is greater than 15 ft., add this amount. If line
length is less than 15 ft., remove this amount.
