Atwood Furnace Repair Manual

The Atwood Furnace is a high-efficiency heating system designed for residential and light commercial applications. This manual covers the Atwood 8500-IV series furnace with features including electronic ignition, variable-speed blower motor, multi-position installation capability, built-in diagnostic LED, safety shut-off controls, and compatibility with natural gas or propane. Below are key sections for safety, features, installation, operation, maintenance, and troubleshooting.

1. Features at a Glance 2. Installation 3. First-Time Setup 4. Specifications 5. Controls and Settings 6. Connecting Gas Supply 7. Operating Procedures 8. Maintenance Schedule 9. Safety Features 10. Regulatory Information 11. Troubleshooting

Features at a Glance

Key components: Burner assembly, heat exchanger, blower motor, gas valve, control board, flame sensor, limit switches, diagnostic LED.

Feature	Description
Electronic ignition	Hot surface igniter for reliable startup
Variable-speed blower	Adjustable airflow for optimal efficiency
Multi-position installation	Can be installed in upflow, downflow, or horizontal configurations
Diagnostic LED	Flashing codes for troubleshooting
Dual fuel capability	Natural gas or propane with proper conversion kit
Safety shut-off	Automatic gas shut-off if ignition fails
Limit switches	Prevents overheating
Flame sensor	Detects flame presence for safety
Pressure switch	Ensures proper venting before ignition
Control board	Microprocessor for system operation

Installation

Unpack and inspect all components. Ensure proper clearances and venting.

Select installation location: Minimum 1-inch clearance from combustible materials.
Install venting: Use approved PVC or metal vent pipe per local codes.
Connect gas supply: Use black iron pipe with proper thread sealant.
Electrical connection: 120V AC power supply with proper grounding.
Connect thermostat: Use 18-gauge low-voltage wiring.

WARNING! Gas appliances can be dangerous if improperly installed. Only qualified technicians should perform installation.

First-Time Setup

Complete installation verification before initial startup.

Gas pressure check: Verify inlet and manifold pressures per specifications.
Venting verification: Ensure proper draft and no obstructions.
Electrical check: Verify proper voltage and polarity.
Initial startup: Follow lighting instructions; observe first ignition cycle.
System calibration: Adjust blower speed and temperature rise as needed.

CAUTION! Test for gas leaks with soap solution before operating.

Specifications

Model Series: 8500-IV
Input Capacity: 40,000-120,000 BTU/hr (varies by model)
Efficiency: 80% AFUE minimum
Fuel Type: Natural gas or propane (with conversion)
Electrical: 120V AC, 60Hz, 3.5 amps max
Venting: Category I or IV depending on configuration
Gas Pressure: Natural gas: 3.5" WC; Propane: 10" WC
Temperature Rise: 35-65°F
Blower Type: Multi-speed direct drive
Dimensions: Varies by model (typically 21"W x 26"H x 34"D)

Controls and Settings

Access control board via front panel. Diagnostic LED provides status codes.

Control Board: POWER switch, FUSE, TERMINAL STRIP, DIP SWITCHES.

Temperature: Thermostat control, fan limit switch. Gas: Pressure regulator, gas valve settings. Blower: Speed taps (COOL, HEAT), delay settings. Safety: Limit switches, roll-out switch, pressure switch, flame sensor. Diagnostic: LED flash codes (1 flash = normal, 2 flashes = pressure switch, etc.).

Connecting Gas Supply

Use approved gas piping materials and proper sizing.

Shut off main gas supply before connecting.
Install sediment trap before gas valve.
Use pipe dope or Teflon tape on threaded connections.
Pressure test: 14" WC for 10 minutes with no drop.
Connect flexible appliance connector if required by code.

Tip: Always use two wrenches when making gas connections to avoid stress on valves.

Operating Procedures

Normal operation sequence: Thermostat call, inducer motor start, pressure switch verification, igniter heating, gas valve opening, flame establishment, blower activation.

Set thermostat to desired temperature.
System will initiate heating cycle automatically.
Observe ignition sequence through viewport.
Listen for proper blower operation after heat exchanger warms.
System will cycle off when thermostat satisfied.

WARNING! Never operate without proper venting. Carbon monoxide hazard exists.

Maintenance Schedule

Annual professional maintenance recommended. Monthly visual inspection by homeowner.

Frequency	Task
Monthly	Check air filter; clean/replace as needed
Annually	Professional inspection and cleaning
Annually	Clean heat exchanger and burners
Annually	Check gas pressure and combustion
Annually	Inspect vent system and clearances
Annually	Test safety controls and limit switches
Every 3-5 years	Replace flame sensor and igniter

Safety Features

Multiple safety systems prevent hazardous operation. Limit Switch: Shuts off gas if overheating detected. Pressure Switch: Prevents operation if venting blocked. Flame Sensor: Shuts gas valve if no flame detected. Roll-out Switch: Shuts off gas if flame rolls out of burner. High Temperature Limit: Additional over-temperature protection.

Regulatory Information

ANSI Z21.47: Certified for US and Canadian standards. CSA 4.3: Gas-fired central furnaces. UL 307A: Oil-fired central furnaces. For support, visit www.atwoodmobile.com or contact 1-800-888-3378. Installation must comply with National Fuel Gas Code NFPA 54 and local codes.

Troubleshooting

Symptom	Possible Cause	Corrective Action
No heat	Thermostat, power, gas supply	Check thermostat setting; verify power; check gas valve open.
Furnace won't start	Safety lockout, pressure switch	Reset power; check venting; verify pressure switch operation.
Short cycling	Dirty filter, limit switch	Replace air filter; check airflow; test limit switch.
Blower won't stop	Fan switch, thermostat	Check fan limit switch; verify thermostat fan setting.
Ignition failure	Igniter, gas valve, flame sensor	Test igniter for continuity; check gas pressure; clean flame sensor.
Unusual noises	Blower, inducer, heat exchanger	Inspect blower wheel; check inducer motor; examine heat exchanger.

Reset: Turn power off for 30 seconds to reset control board.

Service: 1-800-888-3378; www.atwoodmobile.com