Carrier 50NT-B Comfort™ Heat Pump Installation Instructions

Safety Considerations

WARNING: PERSONAL INJURY AND PROPERTY DAMAGE HAZARD

• Continuous fan mode is required for proper functioning. Installation must meet the Required Minimum Dissipation Airflow as outlined in the Leak Dissipation System section.
• Installation and servicing of this equipment can be hazardous due to mechanical and electrical components. Only trained and qualified personnel should install, repair, or service this equipment.
• Untrained personnel can perform basic maintenance functions such as cleaning and replacing air filters. All other operations must be performed by trained service personnel.
• Observe precautions in literature, on tags, and on labels attached to or shipped with the unit, and other safety precautions that may apply.

WARNING: PERSONAL INJURY AND PROPERTY DAMAGE HAZARD

• For continued performance, reliability, and safety, use only approved accessories and replacement parts specified by the equipment manufacturer. Use of non-manufacturer approved parts could invalidate the warranty and result in fire risk, equipment malfunction, and failure.
• Auxiliary devices that may be a POTENTIAL IGNITION SOURCE shall not be installed in the duct work.
• False ceilings or drop ceilings must not be used as a return air duct/plenum.
• This unit is pre-charged with refrigerant. Non-sparking tools are required for any service work on the A2L refrigerant system. If the system is opened, use a refrigerant detector. Open flames or other ignition sources should not be present, except during brazing on evacuated lines.
• Follow all safety codes. Wear safety glasses, protective clothing, and work gloves.

Electrical Safety: Consult local building codes and the National Electrical Code (NEC) NFPA 70, and Canadian Electrical Code CSA C22.1.

Safety Alert Symbol: The symbol ▲ indicates potential personal injury hazards. Always be alert to potential hazards.

Signal Words: DANGER (severe hazards), WARNING (hazards that could cause injury or death), CAUTION (unsafe practices that may cause minor injury or property damage).

WARNING: ELECTRICAL SHOCK HAZARD

Always turn off main power and install lockout tag before installing or servicing. Ensure accessory heater power switch is also off if applicable.

CAUTION: CUT HAZARD

Be aware of sharp sheet metal parts and screws when removing access panels or performing maintenance.

Introduction

This is a self-contained, electrically powered heat pump designed for outdoor installation. Standard units are shipped for horizontal discharge configuration on a ground-level slab but can be converted to downflow (vertical) discharge for rooftop applications.

NOTICE: If replacing gasketing or insulation, ensure materials meet NFPA 90.1 (flame spread/smoke generation) and ASHRAE Standard 62.2 (cabinet insulation) requirements.

Receiving and Installation

Transport and Storage Considerations

This unit uses Puron Advance (R-454B) refrigerant, which is flammable. Follow all applicable regulations for transportation and storage, including unit configuration and quantity limits.

Step 1 – Check Equipment

Identify Unit

Verify unit model and serial number against shipping papers.

Inspect Shipment

Inspect for shipping damage before removing packaging. If damage is found, have it examined by transportation inspectors before removal and file a claim. Notify the distributor immediately of any missing items. Keep parts in original packaging until installation.

Step 2 – Provide Unit Support

Roof Curb

Install accessory roof curb per its instructions, including insulation, cant strips, roofing, and flashing. Ensure ductwork is attached to the curb.

IMPORTANT: Proper gasketing of the unit to the roof curb is critical for a watertight seal. Ensure the curb is level within 1/4 inch (6 mm) for proper drain function.

Kits are available for installing new units on older "G" series roof curbs.

CAUTION: UNIT/STRUCTURAL DAMAGE HAZARD

Ensure sufficient clearance for saw blades when cutting roof curb flanges to avoid damaging the roof or flashing.

Slab Mount

Place the unit on a solid, level pad at least 2 inches (51 mm) above grade. The pad should extend approximately 2 inches (51 mm) beyond the unit casing on all sides. Do not secure the unit to the pad unless required by local codes.

Step 3 – Provide Clearances

Refer to Figures 2 and 3 for required minimum service clearances. Ensure adequate ventilation and outdoor air supply. Prevent fan discharge from recirculating to the outdoor coil. Do not locate the unit in a corner or under an obstruction. Minimum clearance under a partial overhang is 48 inches (1219 mm) above the unit top. Maximum horizontal extension of a partial overhang must not exceed 48 inches (1219 mm).

IMPORTANT: Do not restrict outdoor airflow. Air restrictions can be detrimental to compressor life.

Do not place the unit where water, ice, or snow can damage it. Do not install on carpeting or combustible materials. Slab-mounted units must be at least 2 inches (51 mm) above expected water levels. Do not use the unit if it has been submerged.

Unit Dimensions

Refer to Figure 2 (24-30 Unit Dimensions) and Figure 3 (36-60 Unit Dimensions) for detailed dimensional information.

Roof Curb Dimensions

Refer to Figure 4 (Roof Curb Dimensions) for details on small/common and large roof curbs, including part numbers and dimensions.

Step 4 – Rig and Place Unit

Lifting holes are provided in the base rails. Use appropriate shackles, clevis pins, and straps rated for the unit's weight. Use a spreader bar of sufficient length to prevent rigging straps from damaging the unit.

WARNING: PERSONAL INJURY OR PROPERTY DAMAGE HAZARD

Ensure the roof can support the unit's weight. Use only trained and qualified personnel for rigging and handling. Observe all safety precautions.

WARNING: UNIT FALLING HAZARD

Never stand beneath rigged units or lift over people.

WARNING: PROPERTY DAMAGE HAZARD

When straps are taut, the clevis should be a minimum of 36 inches (914 mm) above the unit top cover.

Inspection

Visually inspect rigging components (shackles, clevis pins, straps) monthly for damage, wear, or deformation. Discard any damaged parts.

Step 5 – Select and Install Ductwork

Duct system design and installation must comply with NFPA standards (90A or 90B) and local codes. Select and size ductwork, registers, and grilles according to ASHRAE recommendations.

The unit has duct flanges on the supply and return air openings.

WARNING: PERSONAL INJURY HAZARD

For vertical units, install a 90-degree turn in the return ductwork to prevent objects from falling into the conditioned space. Units with electric heaters require a 90-degree elbow in the supply duct.

Consider the following for ductwork:

• Install field-supplied filters or accessory filter racks in the return-air side.
• Avoid abrupt duct size changes.
• Use flexible connectors with gaskets to prevent vibration and ensure airtight seals. For electric heaters, use fireproof canvas connectors extending 24 inches (610 mm) from the element.
• Size ductwork for maximum required airflow.
• Seal, insulate, and weatherproof all external ductwork and ductwork passing through unconditioned spaces, following SMACNA and ACCA standards.
• Secure all ducts to the building structure and vibration-isolate openings.

Configuring Units for Downflow (Vertical) Discharge

Follow instructions to remove horizontal duct covers and prepare for downflow discharge.

WARNING: ELECTRICAL SHOCK HAZARD

Turn off main power and install lockout tag before performing service.

Ductwork Knockouts: Remove horizontal duct covers to access vertical discharge duct knockouts. Break tabs to remove downflow return and supply knockout covers.

NOTE: Reinstall factory-shipped horizontal duct covers to ensure airtight and watertight openings.

Step 6 – Provide for Condensate Disposal

Comply with local codes for condensate disposal. The unit has a 3/4-inch NPT female fitting for condensate. Drain directly onto the roof (if permitted) or onto a gravel apron. Install a field-supplied condensate trap, ensuring the outlet is at least 1 inch (25 mm) lower than the unit drain-pan connection to prevent overflow. Prime the trap with water. Ensure gravel aprons slope away from the unit.

Step 7 – Install Electrical Connections

CAUTION: UNIT COMPONENT DAMAGE HAZARD

Make all electrical connections per NEC NFPA 70, CSA C22.1, and local codes. Refer to the unit wiring diagram.

Use only copper conductors for field-supplied disconnect switch connections. Do not use aluminum wire.

Ensure high-voltage power is within the unit's operating voltage range. For 3-phase units, ensure phase balance is within 2 percent.

Avoid damaging internal components when drilling panels.

Route field power supply away from potential damage.

WARNING: ELECTRICAL SHOCK HAZARD

The unit cabinet must have an uninterrupted electrical ground. Use approved conduit or a properly connected ground wire.

High-Voltage Connections

Install a field-supplied, waterproof disconnect switch near the unit. Refer to the unit rating plate, NEC, and local codes for fuse/breaker size and wire sizing.

Proceed as shown in Figure 10 for high-voltage connections, referencing the unit wiring label.

Special Procedures for 208-V Operation

WARNING: ELECTRICAL SHOCK HAZARD

Turn off power before making adjustments. To convert for 208V operation, move the black wire from the transformer's 230V terminal to the 208V terminal.

Control Voltage Connections

NOTE: Do not use power-stealing thermostats.

Use 18 AWG (or 16 AWG for runs over 100 ft) color-coded, insulated wires for thermostat connections. Provide a drip loop for control wires.

Standard Connections: Connect low-voltage thermostat leads to the 24V splice box as shown in Figure 10.

If an accessory electric heater is installed, connect its low voltage leads to the factory-supplied leads from the Indoor Fan Board P4 connector.

Leak Dissipation System

The unit features a Puron Advance (R-454B) leak detection and dissipation system. This system includes a refrigerant sensor and a dissipation control board that monitors for leaks. If a leak is detected, the system will energize continuous fan mode and remove calls for cooling/heating. Once the leak is no longer detected, the system will resume normal operation after a delay.

Leak Dissipation Control Board (DSB)

The DSB is located in the control box. It has LED indicators for system status. Refer to Figure 11 for location and Table 1 for test button functions.

Refrigerant Detection Sensor (RDS)

Refer to Figures 12 and 13 for the location of the Refrigerant Detection Sensor.

Required Minimum Dissipation Airflow

Ensure the selected continuous fan speed meets or exceeds the Required Minimum Dissipation Airflow specified in Table 3. Refer to Table 6 for blower speeds and CFM performance.

Minimum Conditioned Space Area

Table 3 specifies the minimum conditioned space area required for proper dissipation. This area should not be used for unit sizing.

Sequence of Operation

Details the operation for Continuous Fan, Cooling Mode, Electric Heating Mode, Heat Pump Heating Mode, Heat Pump Heating with Auxiliary Electric Heat, and Defrost Mode.

Physical Data

Table 3 provides detailed physical data for unit sizes 24 through 60, including shipping weight, compressor quantity, refrigerant type and quantity, metering devices, airflow, pressures, and filter sizes.

Minimum Airflow for Electric Heater Operation

Table 4 specifies the minimum airflow (CFM) required for reliable electric heater operation for each unit size.

Typical Installation

Figure 14 illustrates a typical installation setup, showing the unit, disconnect, power source, and indoor thermostat.

Connection Wiring Schematics

Figures 15 through 20 provide detailed wiring schematics for various voltage and phase configurations (208/230-1-60, 208/230-3-60, 460-3-60). These diagrams are essential for correct electrical connections.

Pre-Start-Up

WARNING: FIRE, EXPLOSION, ELECTRICAL SHOCK AND ENVIRONMENTAL HAZARD

Follow recognized safety practices. Relieve and recover all refrigerant before disturbing compressor terminals. Disconnect all electrical sources before removing compressor plugs. Never attempt to repair soldered connections while the system is under pressure. Do not use a torch to remove components.

Pre-Start-Up Checklist:

• Remove all access panels.
• Read and follow all DANGER, WARNING, CAUTION, and INFORMATION labels.
• Inspect for shipping and handling damage, loose parts, or disconnected wires.
• Check all field and factory wiring connections for tightness and ensure wires do not touch refrigerant tubing or sharp edges.
• Inspect coil fins and straighten if bent.
• Verify outdoor fan blade position and air filter presence.
• Ensure condensate drain pan and trap are filled with water.
• Remove all tools and loose parts.
• Ensure Schrader valve caps are tight.

Start-Up

Check cooling and heating control operation by setting the thermostat to OFF, then FAN ON, then AUTO for both system and fan modes. Observe unit operation.

NOTE: Allow a 5-minute delay before restarting the compressor after it has stopped.

Step 1 – Check for Refrigerant Leaks

WARNING: EXPLOSION HAZARD

Never use air or oxygen-containing gases for leak testing or operating compressors. Use only approved leak detection methods.

Work Procedure: Follow safety protocols, avoid hot work near the unit, and keep ignition sources away. Use an R-454B leak detector (non-sparking, adequately sealed). Calibrate detection equipment for R-454B.

Refrigerant Recovery: If leaks are found, recover refrigerant per decommissioning procedures. If no leaks are found, recover refrigerant and evacuate to 500 microns.

Charging: Charge the unit with Puron Advance (R-454B) using an accurate scale, referring to the unit rating plate. Do not overfill. Label the system with the charge amount. Conduct a follow-up leak test.

Checking and Adjusting Refrigerant Charge

The system is factory charged. Adjustment is only needed if suspected. Use an R-454B leak detector during adjustment. Refer to charging charts (Figure 24) and labels for subcooling or superheat procedures.

NOTE: Allow the system to run for at least 15 minutes before checking charge. Adjustments should be minimal; significant deviations indicate other system issues.

Indoor Airflow and Airflow Adjustments

Recommended cooling airflow is 350-450 CFM per 12,000 Btuh. Heating airflow should produce a temperature rise within the unit's rating plate range.

Ensure supply/return grilles are open and filters are clean.

WARNING: ELECTRICAL SHOCK HAZARD

Disconnect power and tag before changing blower speed.

The unit is factory set for single cooling fan speed. It can be configured for two cooling speeds (normal and enhanced dehumidification) or single speed cooling with a higher speed for electric heat.

Table 5 lists color coding for indoor fan motor leads (Black=High, Blue=Low, etc.).

Table 6 provides dry coil air delivery data for various speeds and static pressures.

NOTE: If accessory electric heat is installed, dry airflow must meet or exceed minimum airflow specified in Table 4.

Continuous Fan Operation

When DEHUM is not used, continuous fan speed matches cooling speed. When DEHUM is used, fan speed depends on the DH control lead status (LOW or HIGH).

WARNING: PERSONAL INJURY AND PROPERTY DAMAGE HAZARD

The lowest continuous fan speed must meet or exceed the Required Minimum Dissipation Airflow (Table 3).

Typical Heat Pump Operation

Figure 21 illustrates typical heat pump operation in cooling mode. Figure 23 illustrates heating mode.

Interface Fan Board (IFB)

Figure 22 shows the Interface Fan Board (IFB) with various connection points for fan speed selection, dehumidification control, and other functions.

Step 3 – Defrost Control

Demand Defrost Mode

The defrost mode is factory set to an initial 60-minute interval but can be adjusted (30, 90, 120 minutes). The control optimizes defrost time based on previous cycles. If defrost periods are consistently short, the interval increases; if consistently long, it decreases. Defrost lasts a maximum of 10 minutes, after which normal heating resumes.

Tables

Table 3: Physical Data - Provides specifications for unit sizes 24-60.

Table 4: Minimum Airflow for Reliable Electric Heater Operation (CFM) - Lists required airflow for electric heat.

Table 6: Dry Coil Air Delivery - Shows CFM and BHP for various motor speeds and external static pressures.

Table 7: Filter Pressure Drop Table (IN. W.C.) - Lists pressure drops for different filter sizes and airflow rates.

Table 8: Wet Coil Pressure Drop (IN. W.C.) - Lists pressure drops with a wet coil.

Table 9: Economizer with 1-in. Filter Pressure Drop (IN. W.C.) - Lists pressure drops for economizer configurations.

Table 10: Electric Heat Pressure Drop Table (in. W.C.) - Lists pressure drops associated with electric heat operation.

Maintenance

Periodic maintenance ensures high performance and minimizes equipment failure. Annual inspection by a qualified service person is recommended.

WARNING: PERSONAL INJURY AND UNIT DAMAGE HAZARD

Maintenance requires expertise. Do not attempt if unqualified, except for procedures in the Owner's Manual.

WARNING: ELECTRICAL SHOCK HAZARD

Turn off power and tag before performing maintenance. Use caution when removing panels and avoid placing combustibles near the unit.

CAUTION: UNIT OPERATION HAZARD

Label wires before disconnecting to prevent errors during reassembly.

Minimum Maintenance Requirements:

• Inspect air filter monthly; clean or replace as needed.
• Inspect indoor coil, drain pan, and condensate drain each cooling season.
• Inspect blower motor and wheel each cooling season.
• Check electrical connections and controls each cooling season.

Indoor Blower and Motor

Motors are pre-lubricated. Clean accumulated dirt and grease from the blower wheel and motor annually for optimal performance.

WARNING: ELECTRICAL SHOCK HAZARD

Disconnect power and tag before cleaning the blower motor and wheel.

Cleaning Procedure: Remove blower assembly, disconnect motor plugs, clean wheel and housing with a brush and vacuum. Reassemble carefully, ensuring proper alignment and setscrew tightening.

Troubleshooting

Refer to Table 11 for troubleshooting symptoms, causes, and remedies.

Sequence of Events - Dissipation Mode: Describes the system's response to refrigerant leaks detected by the sensor.

Flash Codes / Actions: Provides guidance for interpreting status codes from the dissipation board (Table 12). Power cycling is the first step for most codes. If issues persist, sensor or board replacement may be necessary.

Table 11: Troubleshooting Chart - Lists common symptoms like compressor/fan not starting, noise, cycling issues, and provides causes and remedies.

Table 12: Dissipation Board Status Code Descriptions - Details flash codes and their meanings.

Start-Up Checklist

A checklist is provided for preliminary information, pre-start-up checks, and start-up procedures including electrical, temperatures, and pressures. This checklist should be removed and stored in job files.

Decommissioning

This section outlines the procedure for safely decommissioning the unit, including refrigerant recovery.

Work Procedure: Instruct personnel, have fire extinguishers ready, avoid ignition sources, and ensure electrical power is available for recovery equipment.

Refrigerant Recovery: Use an R-454B leak detector. Shut off power and gas lines. Recover refrigerant using appropriate equipment and cylinders suitable for R-454B. Follow manufacturer instructions for recovery machines. Do not overfill cylinders. Record recovered amounts. If refrigerant was not recovered, do not use the decommissioned label.

Compressor/Oil Removal: Evacuate compressors/oils to 200 microns or less before removal. Use crankcase electric heat if needed. Do not use a torch. Dispose of oil-contaminated material per local codes.