Armstrong Oil Furnace Model LUF80C84 Service Manual

The Armstrong LUF80C84 is an 80,000 BTU oil-fired furnace designed for residential heating applications. This service manual covers installation, operation, maintenance, troubleshooting, and repair procedures for qualified technicians. The furnace features Beckett AFG oil burner, primary control with safety lockout, cad cell flame detection, and compatibility with standard heating systems. Below are key sections for safety, specifications, installation, operation, maintenance, and troubleshooting.

1. Safety Information 2. Specifications 3. Installation Requirements 4. Electrical Wiring 5. Fuel System Setup 6. Venting Requirements 7. Startup Procedure 8. Operating Instructions 9. Maintenance Schedule 10. Troubleshooting Guide 11. Parts List

Safety Information

WARNING: This furnace contains high voltage electrical components and operates with combustible fuel. Only qualified technicians should perform service procedures.

Hazard	Precaution
Electrical Shock	Disconnect power before servicing; use lockout/tagout procedures
Fuel Fire/Explosion	Shut off fuel supply before working on burner or fuel lines
Hot Surfaces	Allow furnace to cool before servicing; wear protective gloves
Carbon Monoxide	Ensure proper venting; test for CO leaks after service
Moving Parts	Disconnect power before accessing blower or motor components

Specifications

Model: LUF80C84
Input Capacity: 80,000 BTU/H
Output Capacity: 64,000 BTU/H (80% AFUE)
Fuel Type: No. 2 Heating Oil
Burner: Beckett AFG with 0.75-1.25 GPH nozzle range
Motor: 1/6 HP, 115V
Electrical: 115V/60Hz/1Ph
Flue Size: 5" minimum
Dimensions: 55" H x 21" W x 29" D
Weight: 185 lbs

Installation Requirements

Proper installation is critical for safe and efficient operation.

Location: Install in dry, well-ventilated area with adequate clearance (24" front, 6" sides, 6" rear)
Combustion Air: Provide adequate combustion air per local codes
Floor Protection: Non-combustible floor pad required if installed on combustible flooring
Clearances: Maintain minimum clearances to combustible materials as specified
Leveling: Ensure furnace is level for proper drainage and operation

WARNING! Installation must comply with NFPA 31, local codes, and manufacturer specifications.

Electrical Wiring

All electrical connections must be made by qualified electrician following NEC guidelines.

Connection	Specification
Line Voltage	115V, 15A dedicated circuit with disconnect
Thermostat	24V, 2-wire heat only or heat/cool
Grounding	Proper equipment grounding required
Primary Control	Beckett or equivalent with safety lockout
Motor	PSC type, thermally protected

Fuel System Setup

Proper fuel delivery is essential for efficient combustion.

Oil Tank: Located within 25 feet of furnace; below burner level requires two-pipe system
Fuel Line: 3/8" copper tubing with shutoff valve at tank and furnace
Filter: Install 10-micron filter in fuel line
Nozzle: Beckett 0.85-80A or equivalent for proper flame pattern
Pump Pressure: Set to 100 PSI; adjust for proper combustion

CAUTION! Test for fuel leaks before startup using approved methods.

Venting Requirements

Proper venting ensures safe removal of combustion gases.

Type: Category I venting required
Material: Galvanized steel, AL29-4C, or listed vent pipe
Size: 5" minimum diameter
Height: Minimum 15 feet total; 2 feet above roof penetration
Clearances: Maintain 1" clearance to combustible materials
Draft: -0.02 to -0.04 W.C. overfire draft

Startup Procedure

Follow this sequence for initial startup or after service.

Verify all connections: electrical, fuel, venting
Fill fuel line: Open shutoff valves; purge air from system
Check thermostat: Set to call for heat
Monitor startup: Listen for proper ignition sequence
Test safety controls: Verify limit controls and flame safety
Measure combustion: CO2: 9-12%, Smoke: 0-1, Stack temp: 300-500°F
Adjust settings: Fine-tune air band and pump pressure

Operating Instructions

Normal operation should be quiet and efficient.

Cycle Sequence: Thermostat call → inducer starts → prepurge → ignition transformer energizes → fuel valve opens → flame established → blower starts after heat exchanger warms → normal operation → thermostat satisfied → fuel valve closes → postpurge → system off.

Normal Indicators: Steady flame, quiet operation, even heat distribution, no unusual odors.

Maintenance Schedule

Interval	Procedure
Annual	Complete combustion chamber inspection and cleaning
Annual	Replace nozzle, oil filter, and air filter
Annual	Test safety controls and electrical components
Seasonal	Check and clean flame sensor/cad cell
Seasonal	Lubricate motor bearings if required
Monthly	Visual inspection for leaks or damage

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No ignition	No fuel, ignition failure, cad cell dirty	Check fuel supply, clean igniter, replace cad cell if needed
Lockout	Safety lockout activated	Reset primary control; diagnose cause of lockout
Smoky flame	Air adjustment, worn nozzle	Adjust air band, replace nozzle, check combustion
Noisy operation	Motor bearings, pump cavitation	Lubricate or replace motor, check fuel supply
Short cycling	Dirty filter, high limit tripping	Replace filter, check airflow, verify limit control
Fuel odor	Leaks in fuel system	Locate and repair leaks; check fittings and connections

Parts List

Burner Assembly: Beckett AFG Complete
Nozzle: 0.85-80A (Beckett 20325)
Ignition Transformer: 10,000V (Beckett 20032)
Primary Control: Beckett 396703 or equivalent
Cad Cell: Beckett 20042
Motor: 1/6 HP, 1075 RPM
Blower Wheel: 10" diameter
Heat Exchanger: LUF80C84-HE01
Limit Control: Fan/Limit 140°F-90°F

Technical Support: Armstrong Air Technical Service 1-800-448-5872

Parts Ordering: www.armstrongair.com/parts