Lennox G14 Pulse Furnace Service Manual

The Lennox G14 Pulse Furnace is a high-efficiency gas furnace featuring pulse combustion technology, electronic ignition system, variable-speed blower motor, and advanced diagnostic controls. This service manual covers installation, operation, maintenance, troubleshooting, and repair procedures for qualified HVAC technicians. Below are key sections for safety, technical specifications, installation guidelines, maintenance procedures, and troubleshooting.

1. Technical Specifications 2. Installation Guidelines 3. Operating Instructions 4. Maintenance Procedures 5. Control System Overview 6. Electrical Connections 7. Gas System Components 8. Venting Requirements 9. Diagnostic Codes 10. Safety Information 11. Troubleshooting Guide

Technical Specifications

Key components: Pulse combustion system, electronic ignition, variable-speed blower, diagnostic control board, heat exchanger assembly.

Specification	Description
Input Capacity	40,000 - 120,000 BTU/H (depending on model)
AFUE Rating	Up to 96% efficiency
Gas Type	Natural Gas or LP (with conversion kit)
Electrical Requirements	120V AC, 60Hz, 15 Amp circuit
Blower Motor	Variable-speed ECM motor
Combustion System	Pulse combustion technology
Venting	PVC pipe (2-inch diameter)
Dimensions	Varies by model (typically 21"W x 26"D x 40"H)
Weight	120-180 lbs (depending on model)
Operating Pressure	3.5" WC natural gas, 10" WC LP

Installation Guidelines

Proper installation is critical for safe and efficient operation.

Location selection: Install in dry, well-ventilated area with adequate clearance.
Gas connection: Use approved gas pipe and fittings; pressure test before operation.
Electrical wiring: Connect to dedicated 15-amp circuit with proper grounding.
Venting system: Install PVC vent pipes according to manufacturer specifications.
Ductwork: Ensure proper sizing and sealing of supply and return ducts.

WARNING! Installation must be performed by qualified HVAC technician. Improper installation can cause fire, explosion, or carbon monoxide poisoning.

Operating Instructions

Startup and normal operation procedures.

Power up: Turn on electrical power and gas supply.
Thermostat setting: Set thermostat to desired temperature.
System check: Listen for proper ignition sequence and burner operation.
Normal operation: System will cycle automatically based on thermostat demand.
Shutdown: Turn off thermostat and disconnect power for extended non-use.

CAUTION! Never operate furnace without proper venting. Ensure combustion air openings are unobstructed.

Maintenance Procedures

Monthly: Check air filter; clean or replace as needed.
Seasonal: Inspect vent system for obstructions.
Annual: Professional inspection of heat exchanger, burners, and safety controls.
Blower maintenance: Clean blower wheel and housing annually.
Combustion system: Inspect pulse combustion components for proper operation.
Electrical components: Check wiring connections and control board.
Gas system: Verify gas pressure and check for leaks.

Control System Overview

Integrated furnace control board with diagnostic LED indicators.

Control Board Features: Microprocessor-based control, diagnostic LED, safety lockout, blower control, ignition sequence control.

LED Flash Codes: 1 flash - Normal operation, 2 flashes - Pressure switch fault, 3 flashes - Ignition failure, 4 flashes - Flame sense fault, 5 flashes - High limit switch open, 6 flashes - Rollout switch open, 7 flashes - Blower fault.

Electrical Connections

Wiring diagram and connection points.

Power supply: 120V AC connection to terminal block.
Thermostat connections: R, W, G, Y terminals for system control.
Blower motor: ECM motor with variable speed control.
Safety controls: Limit switches, pressure switches, flame sensor.
Grounding: Proper equipment grounding required.

Tip: Always disconnect power before servicing electrical components.

Gas System Components

Gas valve, manifold, burners, and combustion chamber.

Gas valve: Regulates gas flow to combustion chamber.
Manifold assembly: Distributes gas to pulse burners.
Combustion chamber: Stainless steel construction for pulse combustion.
Pressure regulator: Maintains proper gas pressure.
Safety shutoff: Automatic gas shutoff in case of system fault.

WARNING! Gas system work must be performed by qualified technician. Always check for gas leaks after servicing.

Venting Requirements

PVC vent pipe installation guidelines.

Vent pipe: 2-inch diameter Schedule 40 PVC. Maximum vent length: 40 feet horizontal, 20 feet vertical. Minimum slope: 1/4 inch per foot toward furnace. Combustion air: Separate intake pipe required. Vent termination: Minimum 12 inches above ground level, 3 feet from operable windows.

Diagnostic Codes

LED flash code interpretation and corrective actions.

Flash Code	Description	Corrective Action
1 Flash	Normal Operation	No action required
2 Flashes	Pressure Switch Fault	Check vent system, pressure switch tubing
3 Flashes	Ignition Failure	Check gas supply, ignition system
4 Flashes	Flame Sense Fault	Clean flame sensor, check grounding
5 Flashes	High Limit Switch	Check airflow, filter, duct restrictions

Safety Information

Critical safety warnings and precautions.

DANGER! Carbon monoxide hazard - ensure proper venting and combustion air. Fire hazard - maintain clearances to combustible materials. Electrical shock hazard - disconnect power before servicing. Explosion hazard - check for gas leaks before energizing system.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No heat	Power outage, thermostat setting, gas valve closed	Check power, thermostat, gas supply
Furnace won't start	Safety lockout, blown fuse, door switch	Reset system, check fuses, ensure doors closed
Short cycling	Dirty filter, restricted airflow, high limit	Replace filter, check ducts, verify limit switch
Unusual noises	Loose components, blower issues, combustion problems	Inspect and tighten components, check blower
Poor heating	Undersized unit, duct leaks, gas pressure	Verify sizing, seal ducts, check gas pressure

Reset Procedure: Turn thermostat off, disconnect power for 30 seconds, restore power, turn thermostat on.

Technical Support: 1-800-9-LENNOX; www.lennox.com