Carrier 48VT(N) Gas Input, Indoor Airflow, Check Defrost Thermostat, Puron Items, 48VT--A

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Gas Input

48VT-- A

If no refrigerant leaks are found and low cooling performance is suspected, refer to the Checking and Adjusting Refrigerant Charge section.

Gas Input

The gas input does not require checking unless improper heating performance is suspected. If a problem exists, refer to the Start-Up section.

Indoor Airflow

The heating and/or cooling airflow does not require checking unless improper performance is suspected. If a problem exists, be sure that all supply- and return-air grilles are open and free from obstructions, and that the air filter is clean. When necessary, refer to the Indoor Airflow and Airflow Adjustments section to check the system airflow.

Check Defrost Thermostat

The defrost thermostat is usually located on the lowest liquid leaving circuit of the left condenser coil (see Fig. 22). The thermostat closes at 32_F (0_C) and opens at 65_F (18_C).

Puron Items

Metering Device (Thermostatic Expansion Valve & Piston)

This unit uses both a hard shutoff, balance port TXV in the indoor coil and a piston in each side of the outdoor coil. The TXV maintains a constant superheat at the evaporator coil exit (cooling mode) resulting in higher overall system efficiency.

Pressure Switches

Pressure switches are protective devices wired into control circuit (low voltage). They shut off compressor if abnormally high or low pressures are present in the refrigeration circuit. These pressure

switches are specifically designed to operate with Puron (R-410A) systems. R-22 pressure switches must not be used as replacements for the Puron (R-410A) system.

Loss of Charge Switch

This switch is located on the liquid line and protects against low suction pressures caused by such events as loss of charge, low airflow across indoor coil, dirty filters, etc. It opens on a pressure drop at about 20 psig. If system pressure is above this, switch should be closed. To check switch:

1.Turn off all power to unit.

2.Disconnect leads on switch.

3.Apply ohm meter leads across switch. You should have continuity on a good switch.

NOTE: Because these switches are attached to refrigeration system under pressure, it is not advisable to remove this device for troubleshooting unless you are reasonably certain that a problem exists. If switch must be removed, remove and recover all system charge so that pressure gauges read 0 psi. Never open system without breaking vacuum with dry nitrogen.

High-Pressure Switch

The high-pressure switch is located in the discharge line and protects against excessive condenser coil pressure. It opens at 650 psig.

High pressure may be caused by a dirty outdoor coil, failed fan motor, or outdoor air recirculation. To check switch:

1.Turn off all power to unit.

2.Disconnect leads on switch.

3.Apply ohm meter leads across switch. You should have continuity on a good switch.

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Contents Fig. 1 - Unit 48VT-A TABLE OF CONTENTSSAFETY CONSIDERATIONS Installation InstructionsStep 1 - Check Equipment RECEIVING AND INSTALLATIONINTRODUCTION Step 2 - Provide Unit SupportFig. 2 - 48VT-A24-30Unit Dimensions 48VT--AA09146 Fig. 3 - 48VT-A36-60Unit Dimensions 48VT--AA09147 SMALL CURB Fig. 4 - Roof Curb Dimensions48VT ROOF CURB DETAILInspection ACCESS PANELS MUST BE IN PLACE WHEN RIGGINGStep 5 - Rig and Place Unit Rigging/Lifting of Unit See FigStep 6 - Connect Condensate Drain Step 7 - Install Flue HoodStep 8 - Install Gas Piping Fig. 6 - Condensate TrapFig. 7 - Sediment Trap Step 9 - Install Duct ConnectionsConfiguring Units for Downflow Vertical Discharge FIRE OR EXPLOSION HAZARD48VT--A Table 1 - Physical Data - Unit 48VT-AFig. 8 - Supply and Return Duct Opening Horizontal Duct CoversTable 3 - Heating Inputs Table 1 - Physical Data - Unit 48VT-ACont’dTable 2 - Maximum Gas Flow Capacity 48VT--AHigh-VoltageConnections Step 10 - Install Electrical ConnectionsSpecial Procedures for 208-VOperation Control Voltage ConnectionsTransformer Protection Balance Point Setting-Thermidistator HybridPRE-START-UP ThermostatStep 1 - Check for Refrigerant Leaks Step 3 - Start-upHeating and Make Adjust- mentsSTART-UP Step 2 - Unit Sequence of OperationCheck Heating Control Adjust Gas InputFig. 11 - Burner Assembly Check Gas InputNormal Operation Limit SwitchesCheck Burner Flame Airflow and Temperature RiseChecking and Adjusting Refrigerant Charge Step 4 - Start-upCooling and Make Adjust- mentsRollout Switch Indoor Airflow and Airflow AdjustmentsTable 6 - Color Coding for Indoor Fan Motor Leads Gas Heating Fan Speed Set-upContinuous Fan Operation 48VT--A48VT--A Fig. 14 - Interface Fan Board IFBTable 8 - 48VT-AWet Coil Pressure Drop Table 7 - Filter Pressure Drop Table IN. W.C48VT--A UNIT48VT--A Heating48VT--A 129548VT--A 144548VT--A 1448Fig. 15 - 208/230-1-60Wiring Diagram, Unit 48VT-A 48VT AFig. 16 - 208/230-3-60Wiring Diagram, Unit 48VT-A 48VT--AA09209 50VT500173 REV Fig. 17 - Cooling Charging Table-Subcooling48VT--A A09099Air Filter MAINTENANCECleaning the Blower Motor and Wheel Indoor Blower and MotorFig. 18 - Blower Housing and Flue Collector Box Limit SwitchInduced Draft combustion air Blower Assembly Fig. 19 - Unit Access PanelsRefrigerant Circuit Electrical Controls and WiringOutdoor Fan Fig. 20 - Removal of Motor and Blower WheelHigh-PressureSwitch Pressure SwitchesLoss of Charge Switch Gas InputPage Fig. 24 - Refrigerant Circuit HPS - High Pressure SwitchLCS - Loss of Charge Switch AccuraterMetering De viceUNIT OPERATION AND SAFETY HAZARD TROUBLESHOOTINGSTART-UPCHECKLIST Synthetic Roof Precautionary ProcedurePURONR R-410AQUICK REFERENCE GUIDE 48VT--ASYMPTOM 48VT--ATable 12 - Troubleshooting Guide-Heating Table 13 - Troubleshooting Guide-LEDStatus Codes48VT--A TEMPERATURES Remove and Store in Job FilesI. PRELIMINARY INFORMATION MODEL NO PRESSURESEdition Date 04/09 48VT--ACatalog No 48VT---05SI Replaces 48VT---04SI
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