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508133G01 / 31-5000715

Page 19 of 25

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.

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

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 12. Operation Mode Jumper

Summary of Contents for NS18HMA

Page 1: ...ion and service performed by unqualified persons can result in property damage personal injury or death WARNING Sharp metal edges can cause injury When installing the unit use care to avoid sharp edge...

Page 2: ...ll safety codes Wear safety glasses and work gloves Use quenching cloth for brazing operations Have fire extinguisher available Read these instructions thoroughly and follow all warning or cautions at...

Page 3: ...m building not to exceed 1 4 per foot Figure 1 Slab Mounting Install on a Solid Level Mounting Pad The outdoor section is to be installed on a solid foundation This foundation should extend a minimum...

Page 4: ...warranty will be void if the drier is not installed Installation of Line Sets DO NOT fasten liquid or suction lines in direct contact with the floor or ceiling joist Use an insulated or suspension typ...

Page 5: ...listed in Table 3 Between 51 and 150 Linear Feet Crankcase heater and nonbleed port TXV factory installed No additional components required Vertical vapor riser must be sized to the vapor riser liste...

Page 6: ...iquid line size shaded row on the outdoor tonnage C Select the actual Total Linear Length of your system shown at the top of the table D The elevation listed in the table is the maximum allowed for th...

Page 7: ...ponents including line set and indoor coil must be an AHRI match with the unit in order to fulfill unit warranty requirements Fire Explosion and Personal Safety hazard Failure to follow this warning c...

Page 8: ...around the stubbed end of the check expansion valve and lightly lubricate the connector threads and expose surface of the Teflon ring with refrigerant oil 4 Attach the stubbed end of the check expans...

Page 9: ...ain round Do not crimp end of the line Remove service cap and core from both the vapor and liquid line service ports 1 2 LIQUID LINE SERVICE VALVE SERVICE PORT CORE SERVICE PORT CAP SERVICE PORT CORE...

Page 10: ...all water saturated cloths WHEN BRAZING LINE SET TO SERVICE VALVES POINT FLAME AWAY FROM SERVICE VALVE PREPARATION FOR NEXT STEP 7 WRAP SERVICE VALVES To help protect service valve seals during brazin...

Page 11: ...sig 1034 kPa Open the valve on the high side of the manifold gauge set in order to pressurize the line set and the indoor unit E After a few minutes open one of the service valve ports and verify that...

Page 12: ...r liquid refrigerant Open the manifold gauge valve 1 to 2 psig in order to release the vacuum in the line set and indoor unit G Perform the following Close manifold gauge valves Shut off HFC 410A cyli...

Page 13: ...1 is jumpered to Y2 in the outdoor unit Note that the published performance data is based upon the use of a two stage thermostat Refer to the NS18HMA field wiring diagram for a conventional 24VAC sing...

Page 14: ...hermostat Control Options Size Circuit and Install Service Disconnect Switch Refer to the unit nameplate for minimum circuit ampacity and maximum fuse or circuit breaker HACR per NEC Install power wir...

Page 15: ...100 30m 18 Temperature Rating 35 C Minimum More than 100 30m 16 Table 7 Conventional 24VAC Thermostat Wiring Route High Voltage and Ground Wires Any excess high voltage field wiring should be trimmed...

Page 16: ...RMOSTAT W L Y2 Y1 O DS C I I R DF TST Y1 O C W1 R G TC TO ACC2 ACC1 Y1 O DH C W2 W1 R G DS W2 FOR SINGLE STAGE OPERATION INSTALL A JUMPER BETWEEN Y1 TO Y2 ON THE OUTDOOR UNIT TERMINAL STRIP Figure 9 C...

Page 17: ...If the intended capacity for the application is 3 or 5 Ton skip this section The units are field convertible to 2 Ton or 4 Ton to efficiently perform for the required application If the intended capa...

Page 18: ...itiate the Charge Mode A heating blower demand must also be provided to initiate high speed blower operation on the indoor unit The compressor and outdoor fan motor will begin to ramp up and reach 100...

Page 19: ...ooling 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 cap...

Page 20: ...late to list the actual field charge Table 11 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 gr...

Page 21: ...testing is completed replace service port cap Tighten finger tight then an additional 1 6 turn To Open Liquid or Suction Line Service Valve 1 Remove stem cap with an adjustable wrench 2 Use service wr...

Page 22: ...in mild detergent and rinsing with cold water Allow filter to dry before reinstalling Replace filters with the arrows pointing in the direction of airflow Dirty filters are the most common cause of p...

Page 23: ...heat pump to automatically switch from heating mode to cooling mode to maintain predetermined comfort settings Many heat pump thermostats are also equipped with an emergency heat mode which locks out...

Page 24: ...Page 24 of 25 508133G01 31 5000715 Issue 2140 Figure 15 Wiring Diagram...

Page 25: ...____________ Actual Amps ______ Rated Volts _______ Actual Volts ________ Condenser Fan Full Load Amps _________ Actual Amps ______ Cooling Mode Suction Pressure ____________________ Liquid Pressure _...

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