Carrier 48GC Single Package Rooftop Unit Service and Maintenance Instructions
This document provides detailed service and maintenance instructions for the Carrier 48GC Single Package Rooftop Gas Heat/Electric Cooling Unit with Puron® (R-410A) Refrigerant, covering nominal tons from 3 to 5.
Safety Considerations
[ALERT] symbol indicates potential for physical injury hazards. Understand signal words: DANGER, WARNING, CAUTION, IMPORTANT, NOTE.
WARNING: R-410A refrigerant systems operate at higher pressures. Do not use R-22 service equipment.
WARNING: Disconnect gas piping when pressure testing above 0.5 psig. Gas valve damage can occur.
WARNING: Use ONLY refrigerants conforming to AHRI Standard 700. Non-certified refrigerants can cause unsafe conditions.
CAUTION: Do not use high-velocity water or compressed air to clean coils; it can bend fins and increase pressure drop.
WARNING: Units with convenience outlets may have multiple disconnects. Check outlet power status before servicing. Lockout/Tagout power switches.
Unit Arrangement and Access
Figures 1 and 2 show typical access panel locations for compressor, outdoor-air opening, indoor coil, flue, and blower sections.
Routine Maintenance
Quarterly inspections should include: return air filter replacement, outdoor hood inlet filter cleaning, condenser coil check, and condensate drain check. Seasonal maintenance includes checking fan motor bolts, compressor mounting bolts, fan blade positioning, control box condition, refrigerant charge, indoor coils, and supply blower motor amperage.
Filters
Return Air Filters: Disposable fiberglass media type. Access via a small lift-out panel on the rear side. Replace as required. Do not operate the unit without return air filters to prevent dirt buildup on heat exchangers and coils, which can cause fires or motor failure.
Outside Air Hood Screens: Permanent aluminum-mesh type. Clean by washing with hot, low-pressure water and mild detergent. Observe flow direction arrows.
Economizer Inlet Air Screen: Retained by filter clips under the top edge of the hood. Remove by opening filter clips.
Manual Outside Air Hood Screen: Secured by a retainer angle. Remove by loosening screws in the top retainer.
Supply Fan (Blower) Section
All 48GC units feature the EcoBlueTM direct drive vane axial fan system, driven by an ECM motor. Fan speed is user-set via the Unit Control Board (UCB), configurable from 40% to 100% of motor's maximum speed.
WARNING: Disconnect and lockout/tagout main power before servicing.
Evaluating Motor Speed: Motor speed is controlled by a 0-10 vdc signal (10 vdc = max rpm).
Selecting Fan Speed: Units are factory set for 7.8 vdc (approx. 78% speed). Speed should be set per job specifications (cfm and ESP) using the Fan Speed Set Up label on the unit's high voltage cover. Charts are provided for calculating vdc based on CFM and ESP. For units with SystemVuTM controls, fan speed settings are accessed via the SystemVu interface.
Low Speed Fan Adjustment: A 2-pin DIP switch on the UCB sets low speed (DIP1 ON = 75% of user set speed).
5-Pin DIP Switch (Single Phase units): Used to set static pressure, tonnage, and motor/drive combinations. Settings are detailed in Table 2.
Troubleshooting the ECM Motor: Motors have built-in protections. Faults like Phase Failure, Locked/Blocked Rotor, Motor Overheated, Power Module Overheated, Line UnderVoltage, and Communication Error are described with their reset triggers (Automatic or Manual). Troubleshooting involves checking line voltage at motor leads and control voltage signal at UCB terminals.
Removing the Motor and Fan Assembly: It is recommended to replace the fan rotor whenever the motor is replaced due to a press-fit design. Steps involve unplugging harness, removing screws, and sliding the assembly out.
Disassembling/Reassembling Motor and Fan Assembly: Detailed steps are provided for removing the rotor, stator, and heat shield, and for reassembling them using specific screws and torque values.
Staged Air Volume: Units with EcoBlueTM technology automatically adjust fan speed: 75% for first stage cooling, 100% for second stage cooling and heating, and 75% for ventilation.
Cooling
WARNING: This system uses R-410A refrigerant, which operates at higher pressures. Use only R-410A compatible equipment.
Condenser Coil
Fabricated with round tube copper hairpins and plate fins. Can be single-row or composite 2-row.
Condenser Coil Maintenance and Cleaning Recommendation
Routine cleaning is essential. Remove surface-loaded fibers with a vacuum or soft brush, working in the direction of the fins. Avoid using water streams that can drive dirt into the coil. Periodic clean water rinse with low-velocity water is recommended, especially in coastal or industrial areas. Use Totaline® environmentally balanced coil cleaner for periodic cleaning. Avoid coil brighteners, acid cleaners, high-pressure washers, and poor quality water.
Two-Row Condenser Coils: Cleaning involves removing the top panel (except around the condenser fan), accessing lower coil clips, removing clips, drawing the inner coil inward to separate for cleaning, cleaning surfaces, flushing between sections, and reassembling.
Totaline Environmentally Balanced Coil Cleaner Application: Mix cleaner in a garden sprayer, wet finned surfaces with water, apply cleaner, allow 10 minutes saturation, and rinse with low-velocity water.
Evaporator Coil
Cleaning: Turn off power, remove access panel, remove economizer (if applicable), slide out filters, clean coil with commercial cleaner or dishwasher detergent, wash both sides, flush with clean water (backflush toward return-air section), flush condensate pan, reinstall components, and replace panels.
Thermostatic Expansion Valve (TXV)
All 48GC units have a factory-installed, non-adjustable TXV designed for Puron® refrigerant. It's a bi-flow, bleed port valve with an external equalizer. The TXV maintains preset superheat by adjusting refrigerant flow based on sensed superheat, suction pressure, and spring pressure.
Replacing TXV: Recover refrigerant, remove TXV support clamp, remove TXV, remove equalizer tube, remove bulb, install new TXV, attach equalizer tube, attach TXV bulb in the same location, route equalizer tube, and sweat the TXV inlet to the liquid line. Use quenching cloth when applying heat.
Refrigerant System Pressure Access Ports
Two 1/4 in. SAE male flare access ports are located on the suction and discharge tubes near the compressor. They feature 2-piece high flow valves with integral check valve cores. Service tools are available to replace the check valve core without recovering the entire charge. Apply compressor refrigerant oil to the O-ring and torque the fitting body to 96 ± 10 in.-lb.
Puron (R-410A) Refrigerant
This unit is designed for Puron® (R-410A) refrigerant only. It is supplied in pink cylinders. For cylinders with dip tubes, place upright; for those without, invert. Remove refrigerant as a liquid and admit it into the discharge line. If adding to the suction line, use a metering/expansion device at the gauge manifold to convert liquid to vapor.
Refrigerant Charge: Amount is listed on the unit's nameplate. Unit panels must be in place during charging. Use standard evacuating techniques. For low-charge cooling, use Cooling Charging Charts (Figures 24-29) based on sub-cooling for various operating conditions.
Compressor
Lubrication: Compressor is factory-charged with polyolester (POE) oil, which is hygroscopic. Avoid exposure to atmosphere.
WARNING: Never use air or gases containing oxygen for leak testing or operating compressors.
Replacing Compressor: Only factory-trained technicians should perform this. POE oil can damage roof membranes; take precautions. Cut tubing with a tubing cutter instead of using a torch.
Compressor Rotation: Scroll compressors require correct rotation. Reverse rotation can cause internal damage. To check: connect gauges, energize compressor, observe suction/discharge pressure drop/rise. If incorrect, turn off power, reverse any 2 of the 3 power leads, and re-energize. If pressures are still incorrect, replace the compressor.
Filter Drier
Replace whenever the refrigerant system is exposed to atmosphere. Use only factory-specified liquid-line filter driers with working pressures no less than 650 psig. A liquid-line filter drier for Puron refrigerant is required on every unit.
Condenser-Fan Adjustment
Adjust fan height by loosening fan hub setscrews, pushing the fan to the desired position, and tightening the set screw to 60 in.-lb. Replace the condenser-fan assembly following the specified screw pattern sequence.
Troubleshooting Cooling System
Table 4 provides solutions for common symptoms like: Compressor and Outdoor Fan Will Not Start, Compressor Will Not Start but Outdoor Fan Runs, Compressor Cycles (Other Than Normally Satisfying Thermostat), Compressor Operates Continuously, Compressor Makes Excessive Noise, Excessive Head Pressure, Head Pressure Too Low, and Suction Pressure Too Low.
Convenience Outlets
WARNING: Units with convenience outlets may have multiple disconnects. Check outlet power status before servicing. Lockout/Tagout power switches.
Two types are offered: non-powered and unit-powered. Both provide a 125 vac GFCI duplex receptacle rated at 15A behind a waterproof access cover.
Installing Weatherproof Cover: A weatherproof while-in-use cover is required by UL. The kit includes a hinged cover, backing plate, and gasket. Installation involves removing the blank cover, installing the backing plate and gasket, mounting the cover, and removing slot fillers for service cords.
Non-Powered Type: Requires field installation of a 125-v, 15-A circuit from elsewhere in the building.
Unit-Powered Type: Includes a factory-installed transformer to step down main power to 115-v. A manual switch with fuse is also included. Primary leads to the transformer are not factory-connected; customer selects the power source.
Duty Cycle: The unit-powered outlet has a duty cycle limitation; avoid continuous loads exceeding 8A for more than 30 minutes per hour.
Maintenance: Periodically test the GFCI receptacle using the TEST button. Check grounding wires and power line phasing if it doesn't trip.
Fuse on Powered Type: Typically a Bussmann® Fusetron® T-15 plug fuse.
Using Unit-Mounted Convenience Outlets: Treat all units as electrically energized until convenience outlet power is also checked and de-energized. Observe National Electrical Code Article 210.
Smoke Detectors
Smoke detectors are available as factory-installed options for supply air, return air (with or without economizer), or both. Their primary function is to shut down the rooftop unit to prevent smoke circulation; they are not life-saving devices.
System
Consists of a 4-wire controller and one or two sensors. Shuts down the unit upon smoke detection.
Controller
Includes housing, PCB, and cover. Connects to one or two sensors. Features LEDs for Power, Trouble, Alarm, and a manual Test/Reset button.
Smoke Detector Sensor
Includes housing, PCB, cover, sampling tube inlet, and exhaust tube. Uses differential sensing to prevent false alarms from gradual environmental changes. Features LEDs for Power, Trouble, Alarm, and Dirty, plus a manual Test/Reset button.
Smoke Detector Locations
Supply Air: Sensor located to the right of the indoor fan, with sampling tube inlet extending through the fan deck. Controller is to the right of the return filter.
Return Air (Without Economizer): Sampling tube across the return air opening on the unit basepan. Sensor mounted on a bracket high on the partition between return filter and controller.
Return Air (With Economizer): Sampling tube inserted through economizer housing side plates, across the return air opening. Sensor mounted similarly to the non-economizer version.
Completing Installation of Return Air Smoke Detector: Involves removing the sensor/plate, rotating the plate for correct orientation, securing it, and connecting tubing to the sampling tube.
FIOP Smoke Detector Wiring and Response: Configured for automatic unit shutdown. NC contact opens on alarm, de-energizing the ORN conductor. RTU Open controls also initiate FSD sequence. Six conductors are provided for field use for annunciation.
Sensor and Controller Tests
Sensor Alarm Test: Uses a test magnet to check sensor's ability to signal an alarm. Hold magnet for 7 seconds to activate Alarm LED, then 2 seconds to reset.
Controller Alarm Test: Press controller's test/reset switch for 7 seconds to activate Alarm LED, then 2 seconds to reset.
Dirty Controller Test: Press controller's test/reset switch for 2 seconds; Trouble LED flashes.
Dirty Sensor Test: Hold test magnet on sensor for 2 seconds; Dirty LED flashes. Flashes indicate dirt level (1 flash = 0-25%, 4 flashes = 76-99%).
Changing the Dirt Sensor Test: Default indicates dirt via sensor's Dirty LED and controller's Trouble LED. Operation can be changed by holding test magnet until Alarm LED is on and Dirty LED flashes twice (approx. 60 seconds), then resetting the sensor.
Remote Station Test: Uses a key switch on a test/reset station to initiate and indicate alarm states.
Detector Cleaning: Clean sensor when Dirty LED is continuously flashing or as needed. Disconnect power, remove cover, clean housing and optic plate with vacuum, compressed air, or brush. Use isopropyl alcohol for gasket. Reconnect power and perform alarm test.
Indicators: Normal state: Power LEDs on. Alarm state: Alarm LEDs on. Trouble state: Trouble LEDs on, or Dirty LED flashing for 100% dirty, or wiring faults.
Troubleshooting: Controller's Trouble LED ON indicates sensor issue or wiring fault. Flashing Trouble LED indicates dirty sensors. Sensor's Trouble LED ON indicates dirty sensor, loose cover, or faulty sensor. Power LED OFF indicates no power to controller or sensor.
Protective Devices
Compressor Protection: Internal line-break motor protection for overcurrent and overtemperature. High pressure switch (trip 630 psig, reset 505 psig). Low pressure switch (trip 54 psig, reset 117 psig). Evaporator freeze protection (trip 30°F, reset 45°F).
Supply (Indoor) Fan Motor Protection: Internal overcurrent and over-temperature protection, automatically resets.
Condenser Fan Motor Protection: Internally protected against overtemperature.
Relief Device: Soft solder joint at suction service port provides pressure relief.
Control Circuit, 24-V: Protected by a circuit breaker on the control transformer.
Gas Heating System
Consists of a gas valve, in-shot burners, primary/secondary tubes, and an induced draft fan. Safety switches include Rollout Switch and Limit Switch.
Fuel Types and Pressures
Factory-equipped for natural gas (NG) at elevations under 2000 ft. LP conversion kits are available. Tables 7-10 specify supply line and manifold pressure ranges for NG and LP fuels.
Supply Pressure Switch: LP conversion kits include a low pressure switch that opens the gas valve power if supply pressure drops too low.
Flue Gas Passageways
Inspect flue collector box and heat exchanger by removing the combustion blower wheel and motor assembly and the flue cover. Clean surfaces with a wire brush.
Combustion-Air Blower
Clean periodically for proper airflow and efficiency. Inspect blower wheel every fall and during heating season. Access involves removing the burner partition panel and the induced-draft motor housing.
Burners and Igniters
Main Burners: Inspect annually for deterioration or blockage. Observe flame characteristics and adjust if necessary. Figure 55 shows spark adjustment details.
Gas Valve: 2-stage valves on 3-phase models (except Low NOx), single-stage on single-phase and Low NOx models. Adjust manifold pressure using plastic adjustment screws. Leak check all gas connections.
Limit Switch: Located on the fan deck.
Burner Ignition: Direct spark ignition with 100% lockout. The Integrated Gas Unit Controller (IGC) provides diagnostic display via an LED. Table 11 lists LED error codes for troubleshooting.
Orifice Replacement: Use specified orifice types. Ensure replacement orifices are tight and projection does not exceed maximum values.
Minimum Heating Entering Air Temperature: Specific temperature requirements for standard and stainless steel heat exchangers. An outdoor-air thermostat may be needed for lower mixed-air temperatures.
Troubleshooting Heating System: Table 12 covers issues like burners not igniting, inadequate heating, poor flame characteristics, and burners not turning off. Table 13 details IGC Board LED Alarm Codes.
SystemVu Control System
A comprehensive, communicating unit-management system compatible with Carrier Comfort Network®, Carrier i-Vu®, and Third Party BACnet® systems. Features an integrated display module for easy access, configuration, diagnosis, and troubleshooting. Requires minimal buttons for navigation. The SystemVu interface allows access to inputs/outputs, parameter configuration, and built-in test routines.
Additional SystemVu Installation and Troubleshooting: Refer to the specific manual for SystemVu controllers.
RTU OPEN Control System
An integrated controller providing optimum performance and energy efficiency. Supports stand-alone, Carrier i-Vu® Open, or Third Party BAS. On-board DIP switches select protocols (BACnet, Modbus®, Johnson N2, LonWorks®). Includes supply-air temperature (SAT) sensor; outdoor air temperature (OAT) sensor is part of economizer package.
Sensory/Accessory Installation: Control wiring must be routed through the unit's raceway or secured with conduit. Connect wires to PCB connectors on the RTU Open board.
WARNING: Disconnect and lockout/tag-out power before wiring.
Additional RTU Open Installation and Troubleshooting: Refer to the specific manual for RTU Open controllers.
Economizer Systems
Available as factory-installed or field-installed accessories. Three types: EconoMi$er® 2 (no controller, 4-20 mA signal), EconoMi$er IV (logic control, field-installed accessory), and EconoMi$er X (logic control, factory option).
EconoMi$er® 2: Operated by a 4 to 20 mA signal from a field-supplied controller. Wiring information provided.
EconoMi$er IV (Field-Installed Accessory): Standard sensors include OAT and SAT. Troubleshooting instructions are enclosed. Functional view, typical settings, sensor ranges, and jumper positions are shown. Input/Output logic is detailed in Table 14. OAT sensor has selectable temperature changeover setpoints (48°F to 78°F) via DIP switches. SAT sensor is a 3K thermistor. Ambient temperature lockout switch protects compressors below 42°F.
Control Modes: Outdoor Dry Bulb Changeover (standard), Outdoor Enthalpy Changeover (requires accessory enthalpy sensor), and Differential Enthalpy Control (requires two enthalpy sensors).
EconoMi$er X (Factory Option): Features a W7220 economizer module with LCD and keypad. Expandable with optional sensors (Mixed Air, Outdoor Air, Return Air, CO2). Module provides power and communications for sensors. S-Bus sensors are used for enthalpy control. W7220 detects sensors automatically. Wiring details and menu structure provided.
Checkout: Inspect wiring, review Status menu, and perform Checkout tests for damper operation and outputs.
Troubleshooting: Alarm messages display on the LCD. Alarms can be cleared after the cause is removed. Common alarms include sensor failures, actuator errors, and freeze alarms.
Pre-Start-Up/Start-Up
WARNING: Follow safety practices, wear PPE, do not use a torch to remove components, recover refrigerant, relieve pressure, and ensure compressor terminal cover is in place before applying power.
WARNING: Unit must be electrically grounded per local codes and NEC.
Inspections: Remove access panels, read all labels, inspect for shipping/handling damage, check for oil leaks (indicating refrigerant leaks), leak-test connections, inspect wiring, and straighten coil fins if damaged.
Verify Conditions: Ensure condenser fan blades are positioned correctly, air filters are in place, condensate drain trap is filled, and all tools/loose parts are removed.
Start-Up, General
Ensure unit installation complies with instructions. DDC units require Service Test function for base unit start-up and output verification. Controller configuration is crucial, especially with field accessories.
Additional Installation/Inspection
Inspect field-installed accessories, DDC alarms, and SAT sensor relocation. Inspect special wiring.
Gas Piping
WARNING: Do not store or use flammable vapors/liquids near the unit. If smelling gas, do not light appliances or touch electrical switches; leave building and call gas supplier or fire department.
Check gas piping for leaks. Ensure correct filters are installed. Do not operate unit without return-air filters or outdoor-air inlet screens.
Compressor Mounting
Compressors are internally spring-mounted; do not loosen or remove hold-down bolts.
Internal Wiring
Check and tighten all electrical connections in unit control boxes.
Refrigerant Service Ports
Two 1/4 in. SAE flare ports (suction and discharge) with check valves. Ensure port caps are tight.
Compressor Rotation
CAUTION: Scroll compressors require correct rotation. Reverse rotation can cause damage. Check by observing suction/discharge pressures. If incorrect, turn off power, reverse two power leads, and re-energize.
Cooling
Set thermostat to OFF. Turn on main power. Set system selector to COOL, fan to AUTO. Adjust thermostat below room temperature. Check unit charge. Reset thermostat above room temperature to shut off unit.
Main Burner
Factory set. Check ignition and controls by calling for heat. Adjust airflow for proper temperature rise.
Heating
Purge gas line of air. Turn on electrical and gas supply. Set system selector to HEAT, fan to AUTO/ON. Set heating temperature lever above room temperature. Induced-draft motor starts, then burners light within 5 seconds. Evaporator fan starts 45 seconds after ignition. Adjust airflow for temperature rise. IGC controller manages ignition and fan delays. To shut off, set system selector to OFF.
Ventilation (Continuous Fan)
Set fan switch to ON, system selector to OFF. Evaporator fan operates continuously.
Fastener Torque Values
Specific torque values are provided for various fasteners, including heat shield, stator, fan rotor, limit switch, fan deck bracket, condenser fan motor, condenser fan hub, and compressor mounting bolts.
Start-Up, RTU Open Controls
Refer to the specific RTU Open Controller manual for set-up instructions.
Start-Up, SystemVu Controls
Refer to the specific SystemVu Controller manual for set-up instructions.
Appendix A -- Model Number Nomenclature
Provides a detailed breakdown of the model number structure, explaining each position from Unit Heat Type to Electrical Options. Example: 48GC D L 04 A 2 A 5 - 0 A 0 A 0.
Key elements include:
- Unit Heat Type: 48 = Gas Heat Packaged Rooftop
- Model Series: GC = High Efficiency
- Heat Options: D (Low), E (Medium), F (High), L (Low NOx), S/R/T (Stainless Steel Exchanger)
- Refrig. Systems Options: H, J, K, L, T (Two-Stage Cooling variants)
- Cooling Tons: 04 (3 ton), 05 (4 ton), 06 (5 ton)
- Sensor Options: A (None) through M (various smoke detector and condensate overflow switch combinations)
- Indoor Fan Options: 1 (Standard Static), 2 (Medium Static), 3 (High Static)
- Coil Options: A-S (various fin/tube materials and hail guard options)
- Factory Assigned: 0 (Standard), 1 (LTL)
- Electrical Options: A (None), B (HACR Breaker), C (Non-Fused Disconnect), D (Thru-the-Base), F, N, P
