🔧 Gas Furnace Diagnostic Playbook

(Video Training + Test Included — Master High-Efficiency Furnace Diagnosis)

This complete step-by-step video training with a built-in technician test teaches HVAC techs how to accurately diagnose and service 96% high-efficiency gas furnaces. Designed by field experts, this proven process covers everything from the thermostat call to full system shutdown — with multimeter test points, wiring guides, safety reminders, and real-world troubleshooting examples.

🎥 What’s Included in This Training Package:

• Full on-demand video walkthrough with visuals for each step

• Printable diagnostic SOP with color-coded wiring and field notes

• End-of-training technician test to validate learning

• Perfect for service tech onboarding, training day modules, or field refreshers

✅ Order of Operations: 96% Gas Furnace Diagnosis

1. Thermostat Call for Heat

• Sends 24V from R to W

• Use meter to confirm 24V at W terminal

• Bypass thermostat to isolate wiring issues

🔍 Keywords: HVAC thermostat wiring, no heat call, 24V signal test

2. Inducer Motor & Pressure Switch

• Inducer starts (120V)

• Pressure switch confirms draft (24V closure)

• Test tubing, drains, and venting if pressure switch fails

🔍 Keywords: inducer motor test, pressure switch not closing, furnace startup failure

3. Igniter Energizes

• HSI glows or spark clicks

• 120V across igniter leads

• Resistance check: 40–200 ohms

🔍 Keywords: igniter not glowing, HVAC hot surface igniter, flame failure diagnosis

4. Gas Valve Opens

• Receives 24V signal from control board

• Confirm gas pressure: 3.5" WC NG / 10" WC LP

• If valve gets power but no gas → issue with valve or supply

🔍 Keywords: gas valve no ignition, furnace not heating, gas pressure check

5. Burners Ignite

• Flame should spread evenly

• Delays indicate dirty burners or crossover issues

🔍 Keywords: burners not lighting, delayed ignition, furnace flame rollout

6. Flame Sensor Confirms Flame

• Signal: 2–6 µA DC required to stay lit

• Clean or replace sensor if low/no reading

🔍 Keywords: flame sensor microamp test, furnace shuts off after lighting

7. Blower Motor Starts

• Starts 30–60 seconds post-ignition

• PSC motor: 120V and capacitor

• ECM motor: 24V signal

🔍 Keywords: blower not running, capacitor test, ECM blower troubleshooting

8. Safety Switches & Limits

• High Limit, Rollout, and Condensate safety switches must remain closed

• Open switches = system lockout

🔍 Keywords: high limit tripped, rollout switch error, condensate safety drain

9. Normal System Shutdown

• Thermostat ends call → burners off → post-purge → system off

🔍 Keywords: HVAC shutdown cycle, furnace shuts down properly, normal heat cycle

🎯 Color-Coded HVAC Wiring Key

Low Voltage (24V)

• 🔴 R = 24V Hot

• ⚪ W = Heat Call

• 🔵/⚫ C = Common

• 🟢 G = Fan

• 🟡 Y = Cooling

High Voltage (120V)

• ⚫ Black = Line Hot

• ⚪ White = Neutral

• 🟢 Green = Ground

• 🟤 Brown = Capacitor leads

🚨 Technician Safety Reminders

• Always meter to verify wiring — don’t assume color

• Shut off power and gas before testing or repairs

• Use calibrated tools and wear PPE

🧠 Who This Training Is For:

• HVAC Technicians (Beginner to Advanced)

• Service Managers & Trainers

• Installers learning service diagnostics

• Companies building internal training libraries

🎓 Training Certification Test Included

• 10+ multiple-choice & scenario-based questions

• Validate understanding after video walkthrough

• Perfect for training days, onboarding, or field readiness checks

  
  

Master 96% gas furnace troubleshooting with this complete video training & test. Covers thermostat signals, inducer motor, igniter, flame sensor, blower, and safeties — ideal for HVAC techs and service managers.