Lennox SGA420 - User Manual

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Summary

Safety

General Safety Instructions

Instructions to keep the unit area clear of combustibles and ensure unobstructed airflow.

Fire and Explosion Hazards

Critical warnings regarding explosion and fire risks, including flood-damaged units.

Improper Service Hazards

Hazards associated with incorrect installation, service, and electrical shock risks.

Fiberglass Wool Precautions

Information on health risks of fiberglass wool and recommended precautions.

Cautionary Notes

Cautionary advice for servicing controls and wiring to prevent errors.

Unit Operation

Before Lighting

Safety checks and procedures required before attempting to light the furnace.

Placing Unit Into Operation

Step-by-step guide for initiating unit operation, including gas valve procedures.

Gas Valve Operation

Detailed instructions for operating the Honeywell VR8205Q/VR8305Q series gas valve.

Burner and Flame Inspection

Burner Flame Inspection

Guidelines for periodically inspecting burner flames to ensure proper unit operation.

Flue Passage and Vent Inspection

Annual inspection of combustion air louvers, vent cap, heat exchanger, and burners.

Service and Maintenance

General Service Recommendations

Advice on maintaining unit efficiency and longevity through yearly servicing.

Servicing Filters

Instructions for checking and replacing unit filters of specified sizes.

Lubrication

Information on motor and bearing lubrication requirements for extended life.

Burner Service

Procedure for examining and cleaning burners, including flame sensor inspection.

Combustion Air System

Combustion Air Inducer Maintenance

Procedure for cleaning the combustion air inducer and its components.

Flue Passageway and Flue Box

Steps for cleaning the flue box, tubes, and reassembling the unit.

Troubleshooting and Parts

Service Reminder Checks

Checklist to verify before calling a qualified service technician for unit inoperability.

Repair Parts Listing

List of available repair parts categorized by section (Gas Heat, Cooling, Electrical).

Modulating Gas Valve (MGV)

MGV Operation and Start-Up

Details on the IMC control of MGVs for heating cycle and start-up procedures.

Manifold Pressures

Required manifold pressures for different gas types and valve configurations.

This document is the User's Information Manual for SGA420, 480, 540, and 600 Rooftop Units, which are commercial HVAC systems with capacities of 35, 40, 45, and 50 TONS respectively. The manual provides essential information for the safe installation, operation, and maintenance of these units.

Function Description:

The SGA series rooftop units are designed to provide heating and cooling for commercial applications. They are equipped with a direct spark ignition system for heating, eliminating the need for a pilot light. The units can be configured with optional features such as an energy recovery wheel, economizer, humiditrol coils, and power exhaust discharge to enhance efficiency and comfort. The heating section utilizes a heat exchanger, burners, and a combustion air inducer to generate heat, while the cooling section employs compressors, condenser coils, evaporator coils, and fans for refrigeration.

Important Technical Specifications:

Models: SGA420, SGA480, SGA540, SGA600
Capacities: 35, 40, 45, and 50 TONS
Filters: Eleven 16 x 25 x 2" (406 x 635 x 51mm) or 16 x 25 x 4" (406 x 635 x 102mm) filters. Filters must be ULC approved or equivalent for use in Canada.
Gas Valve Type: Honeywell VR8205Q/VR8305Q Series Gas Valve (standard). Optional Modulating Gas Valves (MGV) are available.
Manifold Pressures (Standard Gas Valve):
- Natural Gas:
  - 1st Stage: 1.6 in.wg. (0.40 kPa) ± 0.2 in.wg. (±0.05 kPa)
  - 2nd Stage: 3.7 in.wg. (0.92 kPa) ± 0.3 in.wg. (±0.08 kPa)
- Propane (LP) Gas:
  - 1st Stage: 5.5 in.wg. (1.37 kPa) ± 0.2 in.wg. (±0.05 kPa)
  - 2nd Stage: 10.5 in.wg. (2.61 kPa) ± 0.3 in.wg. (±0.08 kPa)
Manifold Pressures (Optional Modulating Gas Valve - MGV):
- GV1 & GV3:
  - Natural: 4.0 in.w.c.
  - LP: 10.8 in.w.c.
- GV4 & GV5:
  - Natural: 3.7 in.w.c.
  - LP: 10.5 in.w.c.
- Minimum Heating Input (MGV):
  - GV1 & GV3: Natural - 4.0 in.w.c., LP - 10.8 in.w.c.
  - GV4 & GV5: Natural - 0.9 in.w.c., LP - 2.6 in.w.c.
Ignitor Spark Gap: 1/8" (3mm)
Electrical: Units may have multiple power supplies.
Control System: Equipped with an IMC (Integrated Modular Control) board for managing heating and cooling operations, including modulating gas valves.

Usage Features:

Automatic Spark Ignition: The unit features an automatic spark ignition system, eliminating the need for manual lighting or a pilot light.
Thermostat Control: Operation is controlled via a thermostat (electromechanical or electronic temperature controls for logic units).
Safety Shutdown: In case of a safety shutdown, the thermostat should be reset to OFF and then to HEAT (for electromechanical) or the main disconnect should be cycled (for logic/electronic controls).
Optional Modulating Gas Valves (MGV): For units with MGVs, the IMC controls the valves to maintain a discharge air temperature of 110°F (default) during heating. The left heat section operates at 25-50% of nameplate heat, and both sections operate at 50-100%. The MGV allows full heating capacity if it fails.
Gas Valve Operation: The gas valve knob should only be pushed in or turned by hand, never with tools.
Gas Leak Procedure: If gas is smelled, do not try to light any appliance, extinguish open flames, avoid electrical switches/phones, leave the building, and immediately call the gas supplier or fire department.

Maintenance Features:

Annual Service: To maintain efficiency and longevity, the equipment must be serviced yearly by a qualified service technician. Failure to provide proof of service may void the warranty.
Filter Replacement: Filters should be checked monthly and replaced when necessary with filters of like kind and size. Note the air flow direction marking on the filter frame.
Burner Flame Inspection: Periodically inspect the burner flame during the heating season. The flame should be mostly blue with some clear yellow streaking at the end.
Flue Passage and Vent Inspection: Annually, before the heating season, inspect the combustion air louvers, vent cap, heat exchanger, burners, and combustion air inducer for corrosion, deterioration, or debris. Remove any obstructions.
Combustion Air Inducer Cleaning: The inducer wheel should be checked and cleaned prior to the heating season, and periodically during the season. This involves turning off power and gas, disconnecting air tubing, removing the inducer from the flue box and vent connector, cleaning the wheel blades and collector box, and reassembling (gasket replacement recommended).
Flue Box Cleaning: Remove the combustion air inducer assembly and flue box cover, then clean the flue box and tubes with a wire brush. Reassemble with new gaskets.
Burner Cleaning: Before each heating season, examine burners for deposits or blockage. Turn off electrical power and gas, open the heat section access panel, remove screws securing burners, clean as necessary, and resecure.
Ignitor Inspection: Remove and check the spark gap of the ignitor (should be 1/8" or 3mm).
Lubrication: All motors are factory-lubricated. Blower shaft bearings are prelubricated and should be relubricated every two years with a lithium base grease (e.g., Alvania 3, Chevron BRB2, Regal AFB2). Add enough grease to purge through the bearings until a bead appears at the seal lip contacts.
Troubleshooting (Service Reminder): If the unit is inoperative, check electrical disconnects, thermostat setting, fuses/breakers, gas valve position, air filters, and access panels before calling a technician.
Parts Ordering: When ordering repair parts, include the complete model number and serial number from the ETL rating plate.
Safety Precautions: Always turn off electrical power to the unit at disconnect switch(es) before performing any service or maintenance. Label all wires prior to disconnection when servicing controls to prevent wiring errors.
Fiberglass Wool Warning: The product contains fiberglass wool. Disturbing insulation during installation, maintenance, or repair may expose individuals to fiberglass wool, which can cause lung cancer, respiratory, skin, and eye irritation. Consult material safety data sheets for more information.