Carrier N4A7 User manual

421 01 5600 00 July/2017
INSTALLATION INSTRUCTIONS
R- 410A 2- Stage Split System Air Conditioner
N4A7 (2 - 5 Tons)
SAFETY CONSIDERATIONS
NOTE: Read the entire instruction manual before starting the
installation.
Improper installation, adjustment, alteration, service, maintenance,
or use can cause explosion, fire, electrical shock, or other
conditions which may cause death, personal injury, or property
damage. Consult a qualified installer, service agency, or your
distributor or branch for information or assistance. The qualified
installer or agency must use factory- authorized kits or accessories
when modifying this product. Refer to the individual instructions
packaged with the kits or accessories when installing.
Follow all safety codes. Wear safety glasses, protective clothing,
and work gloves. Use quenching cloth for brazing operations.
Have fire extinguisher available. Read these instructions
thoroughly and follow all warnings or cautions included in
literature and attached to the unit. Consult local building codes and
current editions of the National Electrical Code (NEC) NFPA 70.
In Canada, refer to current editions of the Canadian electrical code
CSA 22.1.
Recognize safety information. This is the safety- alert symbol !!.
When you see this symbol on the unit and in instructions or
manuals, be alert to the potential for personal injury. Understand
these signal words; DANGER, WARNING, and CAUTION. These
words are used with the safety- alert symbol. DANGER identifies
the most serious hazards which will result in severe personal injury
or death. WARNING signifies hazards which could result in
personal injury or death. CAUTION is used to identify unsafe
practices which would result in minor personal injury or product
and property damage. NOTE is used to highlight suggestions
which will result in enhanced installation, reliability, or operation.
!WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Before installing, modifying, or servicing system, main
electrical disconnect switch must be in the OFF position.
There may be more than 1 disconnect switch. Lock out and
tag switch with a suitable warning label.
EXPLOSION HAZARD
Failure to follow this warning could
result in death, serious personal injury,
and/or property damage.
Never use air or gases containing
oxygen for leak testing or operating
refrigerant compressors. Pressurized
mixtures of air or gases containing
oxygen can lead to an explosion.
!WARNING
INSTALLATION RECOMMENDATIONS
NOTE: In some cases noise in the living area has been traced to
gas pulsations from improper installation of equipment.
1. Locate unit away from windows, patios, decks, etc. where
unit operation sound may disturb customer.
2. Ensure that vapor and liquid tube diameters are appropriate
for unit capacity.
3. Run refrigerant tubes as directly as possible by avoiding
unnecessary turns and bends.
4. Leave some slack between structure and unit to absorb
vibration.
5. When passing refrigerant tubes through the wall, seal
opening with RTV or other pliable silicon- based caulk.
(See Fig. 1.)
6. Avoid direct tubing contact with water pipes, duct work,
floor joists, wall studs, floors, and walls.
7. Do not suspend refrigerant tubing from joists and studs with
a rigid wire or strap which comes in direct contact with
tubing.(See Fig. 1.)
8. Ensure that tubing insulation is pliable and completely
surrounds vapor tube.
9. When necessary, use hanger straps which are 1 in. (25.4
mm) wide and conform to shape of tubing insulation. (See
Fig. 1.)
10. Isolate hanger straps from insulation by using metal sleeves
bent to conform to shape of insulation.
INSULATION
SUCTION TUBE
LIQUID TUBE
OUTDOOR WALL INDOOR WALL
LIQUID TUBE
SUCTION TUBE
INSULATION
CAULK
HANGER STRAP
(AROUND SUCTION
TUBE ONLY)
JOIST
1” (25.4 mm)
MIN
THROUGH THE WALL
SUSPENSION
A07588
Fig. 1 - Connecting Tubing Installation
The outdoor unit contains system refrigerant charge for operation
with AHRI rated indoor unit when connected by 15 ft. (4.57 m) of
field- supplied or factory accessory tubing. For proper unit
operation, check refrigerant charge using charging information
located on control box cover and/or in the Check Charge section of
this instruction.
IMPORTANT: Maximum liquid- line size is 3/8- in. OD for all
residential applications including long line.

2
IMPORTANT: Always install the factory- supplied liquid- line
filter drier. If replacing the filter drier, refer to Product Data Digest
for appropriate part number. Obtain replacement filter driers from
your distributor or branch.
INSTALLATION
CUT HAZARD
Failure to follow this caution may result in personal injury.
Sheet metal parts may have sharp edges or burrs. Use care and
wear appropriate protective clothing and gloves when
handling parts.
CAUTION
!
IMPORTANT: Effective January 1, 2015, all split system and
packaged air conditioners must be installed pursuant to applicable
regional efficiency standards issued by the Department of Energy.
Check Equipment and Job Site
UNPACK UNIT
Move to final location. Remove carton taking care not to damage
unit.
Inspect Equipment
File claim with shipping company prior to installation if shipment
is damaged or incomplete. Locate unit rating plate on unit corner
panel. It contains information needed to properly install unit.
Check rating plate to be sure unit matches job specifications.
Install on a Solid, Level Mounting Pad
If conditions or local codes require the unit be attached to pad, tie
down bolts should be used and fastened through knockouts
provided in unit base pan. Refer to unit mounting pattern in Fig. 2
to determine base pan size and knockout hole location.
For hurricane tie downs, contact local distributor for details and PE
(Professional Engineer) certification, if required by local
authorities.
On rooftop applications, mount on level platform or frame. Place
unit above a load- bearing wall and isolate unit and tubing set from
structure. Arrange supporting members to adequately support unit
and minimize transmission of vibration to building. Consult local
codes governing rooftop applications.
Roof mounted units exposed to winds may require wind baffles.
Consult the Application Guideline and Service Manual -
Residential Split System Air Conditioners and Heat Pumps for
wind baffle construction.
NOTE: Unit must be level to within 2_(3/8 in./ft,9.5 mm/m.)
per compressor manufacturer specifications.
Clearance Requirements
When installing, allow sufficient space for airflow clearance,
wiring, refrigerant piping, and service. Allow 24 in. (609.6 mm)
clearance to service end of unit and 48 in. (1219.2 mm) (above
unit. For proper airflow, a 6- in. (152.4 mm) clearance on 1 side of
unit and 12- in. (304.8 mm) on all remaining sides must be
maintained. Maintain a distance of 24 in. (609.6 mm) between
units. Position so water, snow, or ice from roof or eaves cannot fall
directly on unit.
On rooftop applications, locate unit at least 6 in. (152.4 mm) above
roof surface.
Operating Ambient
The minimum outdoor operating ambient in cooling mode is 55_F
(12.78_C) without accessories and as low as 0_F (- 17.78_C) with
approved low- ambient accessory kits, and the maximum outdoor
operating ambient in cooling mode is 125_F (51.67_C) when
operating voltage is 230v. For 208v applications, the maximum
outdoor ambient is 120_F (48.9_C).
NOTE: Units operating at high stage operation, 208v (or below)
line voltage and at an outdoor ambient 120_F (or greater), may
experience compressor trip.
Make Piping Connections
!WARNING
PERSONAL INJURY AND ENVIRONMENTAL
HAZARD
Failure to follow this warning could result in personal injury
or death.
Relieve pressure and recover all refrigerant before system
repair or final unit disposal. Use all service ports and open
all flow- control devices, including solenoid valves.
Federal regulations require that you do not vent refrigerant
to the atmosphere. Recover during system repair or final
unit disposal.
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
If ANY refrigerant tubing is buried, provide a 6- in (152.4
mm) vertical rise at service valve. Refrigerant tubing lengths
up to 36- in (914.4 mm) may be buried without further
special consideration. Do not bury lines more than 36- in.
(914.4 mm).
3/8- in. (9.53 mm) Dia.
Tiedown Knockouts in
Basepan(2) Places
View From Top
UNIT BASE PAN
Dimension in. (mm)
TIEDOWN KNOCKOUT LOCATIONS in. (mm)
A B C
31–1/2 X 31–1/2
(800 X 800) 9–1/8 (231.8) 6–9/16 (166.7) 24–11/16 (627.1)
35 X 35
(889 X 889) 9–1/8 (231.8) 6–9/16 (166.7) 28–7/16 (722.3)
A05177
Fig. 2 - Tiedown Knockout Locations
Outdoor units may be connected to indoor section using accessory
tubing package or field- supplied refrigerant grade tubing of correct
size and condition. Rated tubing diameters shown in Table 1 are
recommended up to 80 ft. (24.38 m). See Product Data for
acceptable alternate vapor diameters and associated capacity losses.
For tubing requirements beyond 80 ft. (24.38 m), substantial
capacity and performance losses can occur. Following the
recommendations in the Longline Guideline will reduce these
losses. Refer to Table 1 for field tubing diameters. Refer to Table 2
for accessory requirements.
There are no buried- line applications greater than 36- in. (914.4
mm) allowed.
If refrigerant tubes or indoor coil are exposed to atmosphere, they
must be evacuated to 500 microns to eliminate contamination and
moisture in the system.

3
Outdoor Unit Connected to Factory Approved Indoor
Unit
Outdoor unit contains correct system refrigerant charge for
operation with factory approved AHRI rated indoor unit when
connected by 15 ft. (4.57 m) of field- supplied or factory- accessory
tubing, and factory supplied filter drier. Check refrigerant charge
for maximum efficiency.
Refrigerant Tubing Connection Outdoor
Connect vapor and liquid tubes to fittings on vapor and liquid
service valves (see Table 1.) Use refrigerant grade tubing
Sweat Connection
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Service valves must be wrapped in a heat- sinking material
such as a wet cloth while brazing.
Use refrigeration grade tubing. Service valves are closed from
factory and ready for brazing. After wrapping service valve with a
wet cloth, braze sweat connections using industry accepted
methods and materials. Consult local code requirements.
Refrigerant tubing and indoor coil are now ready for leak testing.
This check should include all field and factory joints.
Table 1 – Refrigerant Connections and Recommended Liquid
and Vapor Tube Diameters (In.)
UNIT SIZE
(SERIES)
LIQUID RATED VAPOR*
Connection
&Max.Tube
Diameter
Connection
Diameter
Tube
Diameter
24 3/8 3/4 3/4
36 3/8 7/8 7/8
48 3/8 7/8 1- 1/8
60 3/8 7/8 1- 1/8
* Units are rated with 25 ft. (7.6 m) of lineset. See Product Data sheet for
performance data when using different size and length linesets.
Notes:
1. Do not apply capillary tube or fixed orifice indoor coils to these units.
2. For Tubing Set lengths between 80 and 200 ft. (24.38 and 60.96 m)
horizontal or 35 ft. (10.7 m) vertical differential 250 ft. (76.2 m) Total
Equivalent Length), refer to the Residential Piping and Longline Guide
line- Air Conditioners and Heat Pumps using R- 410A refrigerant.
Install Liquid- Line Filter Drier Indoor
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
1. Installation of filter drier in liquid line is required.
2. Filter drier must be wrapped in a heat- sinking material
such as a wet cloth while brazing.
Refer to Fig. 3 and install filter drier as follows:
1. Braze 5- in. liquid tube to the indoor coil.
2. Wrap filter drier with damp cloth.
3. Braze filter drier to above 5- in. (127 mm) liquid tube.
Flow arrow must point towards indoor coil.
4. Connect and braze liquid refrigerant tube to the filter drier.
A05178
Fig. 3 - Liquid Line Filter Drier
Evacuate Refrigerant Tubing and Indoor Coil
CAUTION
!
UNIT DAMAGE HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Never use the system compressor as a vacuum pump.
Refrigerant tubes and indoor coil should be evacuated using the
recommended deep vacuum method of 500 microns. The alternate
triple evacuation method may be used (see triple evacuation
procedure in service manual). Always break a vacuum with dry
nitrogen.
Deep Vacuum Method
The deep vacuum method requires a vacuum pump capable of
pulling a vacuum of 500 microns and a vacuum gage capable of
accurately measuring this vacuum depth. The deep vacuum method
is the most positive way of assuring a system is free of air and
liquid water. A tight dry system will hold a vacuum of 1000
microns after approximately 7 minutes. See Fig. 4.
500
MINUTES
01234567
1000
1500
LEAK IN
SYSTEM
VACUUM TIGHT
TOO WET
TIGHT
DRY SYSTEM
2000
MICRONS
2500
3000
3500
4000
4500
5000
A95424
A95424
Fig. 4 - Deep Vacuum Graph
Final Tubing Check
IMPORTANT: Check to be certain factory tubing on both indoor
and outdoor unit has not shifted during shipment. Ensure tubes are
not rubbing against each other or any sheet metal or wires. Pay
close attention to feeder tubes, making sure wire ties on feeder
tubes are secure and tight.

4
Table 2 – Accessory Usage
Accessory
Required for Low Ambient
Cooling Applications
(Below 55° F / 12.8° C)
Required for Long Line
Applications*
Required for Sea Coast
Applications
(within 2 miles/3.2 km)
Compressor Start Assist Capacitor and Relay Ye s Ye s No
Crankcase Heater Yes (standard on some units) Yes (standard on some units) No
Evaporator Freeze Thermostat Ye s No No
Hard Shutoff TXV
Ye s
(standard w/factory approved
indoor unit)
Ye s
(standard w/factory approved
indoor unit)
Ye s
(standard w/factory approved
indoor unit)
Liquid Line Solenoid Valve No See Residential Piping
and Long Line Guideline No
Low- Ambient Pressure Switch Ye s No No
Support Feet Recommended No Recommended
Winter Start Control Ye s No No
* For tubing line sets between 80 and 200 ft. (24.38 and 60.96 m) and/or 35 ft. (10.7 m) vertical differential, refer to Residential Piping and Longline Guideline.
Make Electrical Connections
Be sure field wiring complies with local and national fire, safety,
and electrical codes, and voltage to system is within limits shown
on unit rating plate. Contact local power company for correction of
improper voltage. See unit rating plate for recommended circuit
protection device.
NOTE: Operation of unit on improper line voltage constitutes
abuse and could affect unit reliability. See unit rating plate. Do not
install unit in system where voltage may fluctuate above or below
permissible limits.
NOTE: Use copper wire only between disconnect switch and unit.
NOTE: Install branch circuit disconnect of adequate size per NEC
to handle unit starting current. Locate disconnect within sight from
and readily accessible from unit, per Section 440- 14 of NEC.
Route Ground and Power Wires
Remove access panel to gain access to unit wiring. Extend wires
from disconnect through power wiring hole provided and into unit
control box.
!WARNING
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal injury or
death.
The unit cabinet must have an uninterrupted or unbroken
ground to minimize personal injury if an electrical fault should
occur. The ground may consist of electrical wire or metal
conduit when installed in accordance with existing electrical
codes.
Connect Ground and Power Wires
Connect ground wire to ground connection in control box for
safety. Connect power wiring to contactor as shown in Fig. 5.
DISCONNECT
PER N.E.C. AND/OR
LOCAL CODES
CONTACTOR
GROUND
LUG
FIELD GROUND
WIRING
FIELD POWER
WIRING
BLUE
3 PHASE ONLY
A91056
Fig. 5 - Line Power Connections
Connect Control Wiring
Route 24- v control wires through control wiring grommet and
connect leads to control wiring (See Fig. 7). Refer to Installation
Instructions packaged with thermostat.
Use No. 18 AWG color- coded, insulated (35_C minimum) wire. If
thermostat is located more than 100 ft. (30.48 m) from unit, as
measured along the control voltage wires, use No. 16 AWG
color- coded wire to avoid excessive voltage drop.
All wiring must be NEC Class 2 and must be separated from
incoming power leads.
Use furnace transformer, fan coil transformer, or accessory
transformer for control power, 24v/40va minimum.
NOTE: Use of available 24v accessories may exceed the
minimum 40va power requirement. Determine total transformer
loading and increase the transformer capacity or split the load with
an accessory transformer as required.
Final Wiring Check
IMPORTANT: Check factory wiring and field wire connections
to ensure terminations are secured properly. Check wire routing to
ensure wires are not in contact with tubing, sheet metal, etc.
CompressorCrankcaseHeater
When equipped with a crankcase heater, furnish power to heater a
minimum of 24 hr before starting unit. To furnish power to heater
only, set thermostat to OFF and close electrical disconnect to
outdoor unit.
A crankcase heater is required if refrigerant tubing is longer than
80 ft. (24.38 m). Refer to the Application Guideline and Service
Manual Longline Section- Residential Split- System Air
Conditioners and Heat Pumps.
Airflow Selections (ECM Furnaces)
The ECM Furnaces provide blower operation to match the
capacities of the compressor during high and low stage cooling
operation. Tap selections on the furnace control board enable the
installing technician to select the proper airflows for each stage of
cooling. Below is a brief summary of the furnace airflow
configurations
1. The Y2 call for high stage cooling energizes the “Cool” tap
on the control board. The grey wire from cool tap is
connected to tap 5 on the motor. Refer to the furnace
Product Data to find the corresponding airflow. If the
airflow setting for high cooling needs to be switched from
tap 5 to a different tap, jumper a connection from the cool
tap to the desired tap so that the Y2 signal is communicated
via the cool tap to the desired speed tap.
2. The Y1 call for low stage cooling energizes the “Fan” tap
on the control board. The red wire from the fan tap is
connected to tap 1 on the motor. Refer to the furnace
Product Data to find the corresponding airflow. If the
airflow setting for low cooling needs to be switched from
tap 1 to a different tap, jumper a connection from the Fan
tap to the desired tap so that the Y1 signal is communicated
via the Fan tap to the desired speed tap. The Y1 setting will
also govern the continuous fan airflow for the furnace.
Refer to the literature for the furnace for further details.

5
Airflow Selection for Variable Speed Furnaces
The variable speed furnaces provide blower operation to match the
capacities of the compressor during high and low stage cooling
operation. The furnace control board allows the installing
technician to select the proper airflows for each stage of cooling.
Below is a summary of required adjustments. See furnace
installation instructions for more details:
1. Turn SW1- - 5 ON for 400 CFM/ton airflow or OFF for 350
CFM/ton airflow. Factory default is OFF.
2. The A/C DIP switch setting determines airflow during high
stage cooling operation. Select the A/C DIP switch setting
corresponding to the available airflow shown in the furnace
Installation Instructions that most closely matches the
required airflow shown in the air conditioning Product Data
for HIGH speed.
3. The CF DIP switch setting determines airflow during low
stage cooling operation. Select the CF DIP switch setting
corresponding to the available airflow shown in the furnace
installation instructions that most closely matches the
required airflow shown in the air conditioning Product Data
for LOW speed. If a higher or lower continuous fan speed is
desired, the continuous fan speed can be changed using the
fan switch on the thermostat. Refer to the furnace
Installation Instructions for details of how to use this
feature.
Airflow Selection for FVM4 Fan Coils
The FVM4 provides high- and low- stage blower operation to
match the capacities of the compressor at high- and low- stage.
To select recommended airflow, refer to the FVM4 Installation
Instructions. The FVM4 utilizes a control board that allows the
installing technician to select proper airflows. This fan coil has an
adjustable blower- off delay factory set at 90 sec. for high- and
low- stage blower operation.
Install Electrical Accessories
Refer to the individual instructions packaged with kits or
accessories when installing.
Start- Up
CAUTION
!
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this caution may result in personal injury,
equipment damage or improper operation.
SDo not overcharge system with refrigerant.
SDo not operate unit in a vacuum or at negative
pressure.
SCompressor dome temperatures may be hot.
CAUTION
!
PERSONAL INJURY HAZARD
Failure to follow this caution may result in personal injury.
Wear safety glasses, protective clothing, and gloves when
handling refrigerant and observe the following:
SFront seating service valves are equipped with
Schrader valves.
Follow these steps to properly start up the system:
1. After system is evacuated, fully back seat (open) liquid and
vapor service valves.
2. Unit is shipped with valve stem(s) front seated (closed) and
caps installed. Replace stem caps after system is opened to
refrigerant flow (back seated). Replace caps finger-tight and
tighten with wrench an additional 1/12 turn.
3. Close electrical disconnects to energize system.
4. Set room thermostat at desired temperature. Ensure that set
point is below indoor ambient temperature and is set low
enough to energize desired stage. In order to start the system
in low stage, refer to the literature for the installed
thermostat and adjust the set point so that the differential
between the room temperature and the set temperature
energizes Y1.
5. Set room thermostat to COOL and fan control to ON or
AUTO mode, as desired.
6. Operate unit for 15 minutes. Verify system refrigerant
charge by measuring the sub-cooling for low stage and
comparing with the published sub-cool on the rating plate.
7. In order to switch the the system to high stage, refer to the
literature for the installed thermostat and adjust the set point
to a lower value so that the differential between the room
temperature and the set temperature energizes Y2. Verify
system refrigerant charge by measuring the sub-cooling for
high stage and comparing with the published sub-cool on
the rating plate.
SYSTEM FUNCTIONS AND SEQUENCE
OF OPERATION
The N4A7 models utilize a 2-stage cooling indoor thermostat.
With a call for first stage cooling, the outdoor fan and low-stage
compressor are energized. If low-stage cannot satisfy cooling
demand, high-stage is energized by the second stage of indoor
thermostat. After second stage is satisfied, the unit returns to
low-stage operation until first stage is satisfied or until second stage
is required again.
When both first stage and second stage cooling are satisfied, the
compressor will shut off. Therefore, with first stage of cooling Y1
is powered on; and with second stage of cooling Y1 and Y2 are
powered on. When a 2-stage unit is operating at low-stage, system
vapor (suction) pressure will be higher than a standard single-stage
system or high-stage operation.
Compressor Operation
The basic scroll design has been modified with the addition of an
internal unloading mechanism that opens a by-pass port in the first
compression pocket, effectively reducing the displacement of the
scroll.
The opening and closing of the by-pass port is controlled by an
internal electrically operated solenoid. The modulated scroll uses a
single step of unloading to go from full capacity to approximately
67% capacity. A single speed, high efficiency motor continues to
run while the scroll modulates between the two capacity steps.
Modulation is achieved by venting a portion of the gas in the first
suction pocket back to the low side of the compressor, thereby
reducing the effective displacement of the compressor. Full
capacity is achieved by blocking these vents, thus increasing the
displacement to 100%.
A DC solenoid in the compressor controlled by a rectified 24 volt
AC signal in the external solenoid plug moves the slider ring that
covers and uncovers these vents. The vent covers are arranged in
such a manner that the compressor operates at approximately 67%
capacity when the solenoid is not energized and 100% capacity
when the solenoid is energized. The loading and unloading of the
two step scroll is done “on the fly” without shutting off the motor
between steps.

6
NOTE: 67% compressor capacity translates to approximately
75% cooling capacity at the indoor coil.
Check Charge
NOTE:CHARGE IN HIGH STAGE ONLY
Factory charge amount and desired subcooling are shown on unit
rating plate. Charging method is shown on information plate inside
unit. To properly check or adjust charge, conditions must be
favorable for subcooling charging. Favorable conditions exist
when the outdoor temperature is between 70_F and 100_F
(21.11_C and 37.78_C), and the indoor temperature is between
70_F and 80_F (21.11_C and 26.67_C). Follow the procedure
below:
Unit is factory charged for 15ft (4.57 m) of lineset. Adjust charge
by adding or removing 0.6 oz/ft of 3/8 liquid line above or below
15ft (4.57 m) respectively.
For standard refrigerant line lengths (80 ft/24.38 m or less), allow
system to operate in high- stage cooling mode at least 15 minutes.
If conditions are favorable, check system charge by subcooling
method. If any adjustment is necessary, adjust charge slowly and
allow system to operate for 15 minutes to stabilize before declaring
a properly charged system.
If the indoor temperature is above 80_F (26.67_C), and the
outdoor temperature is in the favorable range, adjust system charge
by weight based on line length and allow the indoor temperature to
drop to 80_F (26.67_C) before attempting to check system charge
by subcooling method as described above.
If the indoor temperature is below 70_F (21.11_C), or the outdoor
temperature is not in the favorable range, adjust charge for line set
length above or below 15ft (4.57 m) only. Charge level should then
be appropriate for the system to achieve rated capacity. The charge
level could then be checked at another time when the both indoor
and outdoor temperatures are in a more favorable range.
NOTE: If line length is beyond 80 ft (24.38 m) or greater than 20
ft (6.10 m) vertical separation, See Long Line Guideline for
special charging requirements.
Final Checks
IMPORTANT: Before leaving job, be sure to do the following:
1. Ensure that all wiring is routed away from tubing and sheet
metal edges to prevent rub- through or wire pinching.
2. Ensure that all wiring and tubing is secure in unit before
adding panels and covers. Securely fasten all panels and
covers.
3. Tighten service valve stem caps to 1/12- turn past finger
tight.
4. Leave Owner’s Manual with owner. Explain system
operation and periodic maintenance requirements outlined
in manual.
5. Fill out Dealer Installation Checklist and place in customer
file.
TROUBLESHOOTING
If the compressor fails to operate with a cooling call, the table
below (Resistance table) can be used to verify if there is any
damage to the compressor windings causing system malfunction.
Table 3 – Winding Resistance
Winding
Winding resistance at 70_F+/- 20_F
(21.11_C +/- 11.11_C) by Size
24 36 48 60
Start
(S- C) 1.64 1.52 1.86 1.63
Run
(R- C) 1.30 0.88 0.52 0.39
Troubleshooting N4A7 units for proper switching
between low- and high- stages
Check the suction pressures at the service valves. Suction pressure
should be reduced by 3- 10% when switching from low to high
stage.
NOTE: The liquid pressures are very similar between low- and
high- stage operation, so liquid pressure should not be used for
troubleshooting.
Compressor current should increase 20 to 45% when switching
from low to high stage. The compressor solenoid when energized
in high stage, should measure 24vac at the leads inside control box.
When the compressor is operating in low stage, the 24v DC
compressor solenoid coil is de- energized. When the compressor is
operating in high stage, the 24v DC solenoid coil is energized.
The solenoid plug harness that is connected to the compressor has
an internal rectifier that converts the 24v AC signal to 24v DC.
DO NOT INSTALL A PLUG WITHOUT AN INTERNAL
RECTIFIER.
Unloader Test Procedure:
The unloader is the compressor internal mechanism, controlled by
the DC solenoid, that modulates between high- and low- stage. If
it is suspected that the unloader is not working, the following
methods may be used to verify operation:
1. Operate the system and measure compressor amperage.
Cycle the unloader on and off at 30 second plus intervals at
the thermostat (from low- to high- stage and back to low-
stage). Wait 10 seconds after staging to high before taking a
reading. The compressor amperage should go up or down at
least 20 percent.
2. If step one does not give the expected results, remove the
solenoid plug from the compressor and, with the unit
running and the Thermostat calling for high- stage, test the
voltage output at the plug with a DC voltmeter. The reading
should be 24 volts DC.
3. If the correct DC voltage is at the control circuit molded
plug, measure the compressor unloader coil resistance. The
resistance should be approximately 330 or 1640 ohms
depending on unloader coil supplier. If the coil resistance is
infinite or is grounded, the compressor must be replaced.
MAJOR COMPONENTS
2- Stage Compressor
The 2- stage compressor contains motor windings that provide
2- pole (3500 RPM) operation.
Compressor Internal Relief
The compressor is protected by an internal pressure relief (IPR)
which relieves discharge gas into compressor shell when
differential between suction and discharge pressures exceeds and
550 - 625 psi. The compressor is also protected by an internal
overload attached to motor windings.
Compressor Control Contactor
The contactor has a 24 volt coil and is controlled by Y1 input from
the thermostat
High and Low Pressure Switches
High and low pressure switches are provided in line with the Y1
signal to the contactor for protection. The high pressure switch
mounted on the liquid tube is set to open at 670 psi and higher, and
the low pressure switch mounted on the suction tube opens at a
pressure of 50 psi and lower.
CARE AND MAINTENANCE
For continuing high performance and to minimize possible
equipment failure, periodic maintenance must be performed on this
equipment.

7
Frequency of maintenance may vary depending upon geographic
areas, such as coastal applications. See Owner’s Manual for
information.
A09276 A09277
RVS/Heat Stage 2 O/W2/B
Heat Stage 1 W/W1
Compressor Low Y1
Compressor High Y/Y2
Fan G
24VAC Hot Heating Rh
24VAC Hot Cooling Rc
Dry Contact 1 D1
Dry Contact 2 D2
24VAC Common C
Humidify HUM
Outdoor Air Temp OAT
Remote Room Sensor RRS
OAT/RRS Return
SRTN
SRTN
Outdoor Sensor
Humidifier Solenoid
Valve
Remote Room
Sensor
O
Y1
W1
G
W2
C
Y2
Y1
Y/Y2
R
C
DH
REMOVE J2
JUMPER FOR
HEAT STAGING
REMOVE J1 FOR
DEHUMIDIFY
MODES
Two-Stage
Air Conditione
r
Thermidistat
Variable Speed
Fan Coil
TWO-STAGE
AIR CONDITIONER
THERMIDISTAT
Thermidistat w/ Variable Speed Fan Coil
& 2- Stage Air Conditioner
Thermidistat w/ Variable Speed Furnace
& 2- Stage Air Conditioner
Fig. 6 - Thermidistat Wiring with 2- Stage R- 410A refrigerant Air Conditioner
A09278
Single Stage Furnace with 2- Stage Air Conditioner
A09279
2- Stage Thermostat with Single- Stage Furnace and
2 - Stage Air Conditioner
HUMIDFIER
(24VAC)
Fig. 7 - Generic Wiring Diagrams
(See Thermostat Installation Instruction for specific unit combinations)
LEGEND
24v Factory Wiring
24v Field Wiring
Field Splice Connection
A09306

8
R- 410A REFRIGERANT QUICK REFERENCE GUIDE
SR- 410A refrigerant operates at 50- 70 percent higher pressures than R- 22. Be sure that servicing equipment and
replacement components are designed to operate with R- 410A refrigerant
SR- 410A refrigerant cylinders are rose colored.
SRecovery cylinder service pressure rating must be 400 psig, DOT 4BA400 or DOT BW400.
SR- 410A refrigerant systems should be charged with liquid refrigerant. Use a commercial type metering device in the
manifold hose when charging into suction line with compressor operating
SManifold sets should be 700 psig high side and 180 psig low side with 550 psig low- side retard.
SUse hoses with 700 psig service pressure rating.
SLeak detectors should be designed to detect HFC refrigerant.
SR- 410A refrigerant, as with other HFCs, is only compatible with POE oils.
SVacuum pumps will not remove moisture from oil.
SDo not use liquid- line filter driers with rated working pressures less than 600 psig.
SDo not leave R- 410A suction line filter driers in line longer than 72 hours.
SDo not install a suction- line filter drier in liquid line.
SPOE oils absorb moisture rapidly. Do not expose oil to atmosphere.
SPOE oils may cause damage to certain plastics and roofing materials.
SWrap all filter driers and service valves with wet cloth when brazing.
SA factory approved liquid- line filter drier is required on every unit.
SDo NOT use an R- 22 TXV.
SIf indoor unit is equipped with an R- 22 TXV or piston metering device, it must be changed to a hard shutoff R- 410A
TXV.
SNever open system to atmosphere while it is under a vacuum.
SWhen system must be opened for service, recover refrigerant, evacuate then break vacuum with dry nitrogen and
replace filter driers. Evacuate to 500 microns prior to recharging.
SDo not vent R- 410A refrigerant into the atmosphere.
SDo not use capillary tube coils.
SObserve all warnings,cautions, and bold text.
SAll indoor coils must be installed with a hard shutoff R- 410A TXV metering device.
Copyright 2017 International Comfort Products
Lewisburg, TN 37091 USA
421 00 5600 00