Goodman Furnace GMH95 Service Manual

The Goodman GMH95 is a high-efficiency gas furnace with 95% AFUE rating, featuring two-stage heating operation, variable-speed blower motor, sealed combustion system, diagnostic LED lights, pressure switch monitoring, hot surface ignitor, and multi-speed ECM motor. Designed for residential forced-air heating systems with input capacities ranging from 40,000 to 120,000 BTU/hr. Below are key sections for safety, technical specifications, installation, operation, maintenance, troubleshooting, and parts identification.

Features at a Glance

Key components: Two-stage gas valve, variable-speed ECM blower motor, hot surface ignitor, induced draft motor, primary and secondary heat exchangers, pressure switches, flame sensor, control board with diagnostic LEDs.

Installation Requirements

Unpack and inspect furnace for shipping damage. Verify model number and specifications match requirements.

1. Location requirements: Install in level position with adequate clearance for service access.
2. Combustion air: Ensure adequate fresh air supply for sealed combustion system.
3. Venting: Install PVC vent pipes according to manufacturer specifications.
4. Gas connection: Use proper pipe size and approved gas line materials.
5. Electrical: Connect to proper voltage supply with dedicated circuit.
6. Ductwork: Ensure proper sizing and sealing of supply and return ducts.

WARNING! Gas furnaces produce carbon monoxide; proper installation and venting are critical for safety. Follow all local codes and manufacturer instructions.

Initial Startup Procedure

Complete installation verification before initial startup. Follow systematic startup sequence.

1. Gas pressure check: Verify inlet and manifold gas pressures are within specifications.
2. Venting verification: Confirm proper draft and vent pipe installation.
3. Electrical checks: Verify proper voltage at control board and all safety circuits.
4. System purge: Purge air from gas line before initial ignition.
5. First ignition: Observe ignition sequence and flame characteristics.
6. Temperature rise: Measure temperature rise across heat exchanger.
7. Blower settings: Adjust blower speeds for proper airflow.

CAUTION! Only qualified HVAC technicians should perform startup procedures. Document all measurements and settings.

Technical Specifications

• Model Series: GMH95
• AFUE Rating: 95%
• Input Capacity: 40,000 - 120,000 BTU/hr (varies by model)
• Heating Stages: Two-stage heating operation
• Blower Type: Variable-speed ECM
• Gas Type: Natural gas (LP conversion kits available)
• Electrical: 115V/60Hz/1Ph
• Venting: PVC pipe (2" minimum diameter)
• Static Pressure: 0.1" to 0.8" w.c. maximum
• Temperature Rise: 35°F to 65°F
• Dimensions: Varies by model (typical: 21"W x 21"D x 45"H)

Controls and Components

Integrated furnace control board manages all operations with LED status indicators. Front access panel includes safety switch.

Control Board: Manages ignition sequence, blower operation, safety monitoring, and diagnostic functions.

Safety Devices: Limit switches, pressure switches, flame sensor, rollout switches. Gas Control: Two-stage gas valve with manual shutoff. Blower Assembly: ECM motor with multi-speed capability. Ignition System: Hot surface ignitor with flame proving. Vent System: Induced draft motor and pressure monitoring.

Electrical Connections

115V power supply with dedicated circuit required. Low voltage connections for thermostat and accessories.

1. Disconnect power before servicing electrical components.
2. Verify proper grounding of furnace chassis.
3. Connect thermostat wires to appropriate terminals (R, W, Y, G, C).
4. Check blower motor amperage draw during operation.
5. Verify control board voltage inputs and outputs.

Tip: Use manufacturer wiring diagram for all electrical connections. Document any field modifications.

Gas Supply Requirements

Natural gas supply with proper pressure and volume. LP gas conversion requires approved kit.

1. Gas pipe sizing: Minimum 1/2" pipe for most installations.
2. Gas pressure: Verify 7" w.c. natural gas or 11" w.c. LP at manifold.
3. Leak testing: Test all gas connections with bubble solution.
4. Sediment trap: Install drip leg before gas connection.
5. Shutoff valve: Install approved gas cock within 6 feet of furnace.

WARNING! Gas leaks can cause explosion or fire. Always test for leaks after installation or service.

Venting System

Sealed combustion system uses PVC pipe for intake and exhaust. Follow specific venting requirements.

1. Pipe material: Schedule 40 PVC or CPVC only.
2. Vent sizing: Minimum 2" diameter for most applications.
3. Vent length: Follow manufacturer tables for maximum run lengths.
4. Termination: Proper clearance from windows, doors, and air intakes.
5. Slope: Horizontal runs must slope back toward furnace.
6. Support: Secure vent pipes every 4 feet.

CAUTION! Improper venting can cause carbon monoxide poisoning. Follow all venting specifications exactly.

Maintenance Procedures

Annual maintenance required for optimal performance and safety. Complete maintenance checklist.

1. Filter replacement: Replace air filter monthly during heating season.
2. Heat exchanger inspection: Visually inspect for cracks or corrosion.
3. Blower cleaning: Clean blower wheel and housing annually.
4. Flame sensor: Clean with emery cloth or steel wool.
5. Drain system: Clear condensate trap and drain lines.
6. Electrical: Check all connections and component operation.
7. Combustion analysis: Verify proper combustion parameters.

WARNING! Turn off gas and electrical power before performing maintenance. Only qualified technicians should service gas components.

Regulatory Compliance

UL certified for safety. Meets ANSI Z21.47 standards for gas-fired central furnaces. CSA International certified. Installation must comply with National Fuel Gas Code (NFPA 54), National Electrical Code (NFPA 70), and all local building codes. For technical support, contact Goodman Manufacturing at 1-877-466-8626 or visit www.goodmanmfg.com.

Troubleshooting Guide

Diagnostic Codes: Refer to control board LED flash patterns for specific error codes.

Service Support: 1-877-466-8626; www.goodmanmfg.com