Coleman Furnace Combustion Air Switch Won’t Close: Causes and Fixes

The combustion air switch failing to close on a Coleman furnace is a common safety-related issue that prevents ignition and heating. This article explains why the Coleman furnace combustion air switch won’t close, how to troubleshoot it safely, typical repair steps, estimated costs, and when to call a licensed HVAC technician. The information helps homeowners and maintenance personnel diagnose and address the problem while observing important safety precautions.

Symptom	Likely Cause	Quick Action
Furnace won’t ignite	Blocked intake or fan failure	Check vents and power to inducer fan
Switch clicks but stays open	Faulty switch or wiring issue	Inspect wiring and measure continuity
Intermittent operation	Vacuum leak or corroded tubing	Inspect tubing and connections

How The Combustion Air Switch Works On A Coleman Furnace

The combustion air switch, often called a pressure or vacuum switch, monitors airflow created by the inducer/combustion blower. When the inducer motor runs, it produces a vacuum or pressure differential that closes the switch, signaling the control board to allow ignition. The switch is a safety device: if it fails to close, the furnace control stops the ignition sequence to prevent uncombusted gas from entering the heat exchanger.

Common Symptoms When The Combustion Air Switch Won’t Close

Recognizing symptoms helps narrow causes quickly. Typical signs include repeated ignition lockouts, error codes on the Coleman control board or LED blink patterns, the inducer motor running without ignition, or the furnace cycling into a purge but never lighting. Sometimes the system shows short runtimes or an audible clicking sound from the switch or control board.

Primary Causes Of A Non-Closing Combustion Air Switch

There are several frequent causes. Obstructed combustion intake or exhaust (birds, nests, debris) can prevent the inducer from creating the required vacuum. Inducer motor failure or weak motor reduces airflow. Blocked heat exchanger or flue restrictions create back pressure issues. Cracked, kinked, or disconnected tubing between the inducer housing and switch stops proper pressure transmission. Finally, faulty switches or wiring cause mechanical or electrical failures.

Troubleshooting Steps: Safety First

Before any inspection or repair, turn off power at the furnace switch and the breaker. Shut off the gas supply if work will be inside the burner compartment. If the user is not comfortable working with gas or electrical components, calling a licensed HVAC technician is recommended. Always follow manufacturer’s service manuals and safety guidelines.

Step-By-Step Troubleshooting Guide

1. Check Error Codes And Control Board Lights

Record any LED blink codes or fault codes displayed. Coleman furnaces use specific blink sequences to indicate pressure switch errors or inducer failures. Consult the furnace’s data plate or manual for code interpretation.

2. Inspect Outside Intake And Exhaust Terminals

Visually inspect outdoor intake and exhaust terminations for blockages like leaves, snow, ice, or bird nests. Clear any debris and verify that terminations are properly installed and not crushed or obstructed.

3. Observe Inducer Motor Operation

With power restored and thermostat calling, observe whether the inducer motor runs. If the inducer does not start or runs slowly, it may need replacement, a capacitor (if applicable), or electrical diagnosis. Inducer motors are common failure points.

4. Inspect Pressure Tubing And Connections

Trace the small rubber or vinyl tubing from the inducer housing to the pressure switch. Look for kinks, cracks, hardening, or disconnected fittings. Replace damaged tubing and ensure secure fittings. Even small leaks can prevent the switch from sensing correct pressure.

5. Test The Pressure Switch Mechanically And Electrically

With a multimeter, measure switch continuity while inducing vacuum (or allowing the inducer to run). A functioning switch should show open at rest and close when the inducer produces the required pressure differential. Check the switch’s rated closing pressure on the label to confirm proper behavior.

6. Measure Pressure With A Manometer

For precise diagnostics, connect a manometer to the same point the switch uses and measure the vacuum or pressure during inducer operation. Compare readings to the switch’s required setpoint. This distinguishes between a weak inducer and a bad switch.

7. Check For Heat Exchanger Or Flue Restrictions

Internal blockages, bird nests in the flue, or collapsed vent sections can impede airflow. Inspect and, if needed, professionally clean the heat exchanger and venting system. Corrosion or cracks in the heat exchanger require immediate professional attention.

8. Inspect Wiring And Control Signals

Examine wires to the switch and control board for corrosion, loose terminals, or broken conductors. Measure voltage where applicable and consult wiring diagrams to ensure the control is sending expected signals to the inducer and reading the switch state properly.

Typical Repair Actions And Procedures

After diagnosing the root cause, repairs may include replacing the pressure switch, inducer motor, tubing, or clearing vent obstructions. Minor fixes like replacing tubing or cleaning the intake can often be done by a competent homeowner. More complex tasks—inducer motor replacement, heat exchanger repair, or major wiring work—are best left to licensed HVAC professionals.

Parts, Tools, And Materials Needed

• Multimeter for continuity and voltage checks
• Manometer to measure vacuum/pressure precisely
• Replacement pressure switch specific to Coleman model
• Replacement rubber/vinyl pressure tubing
• Screwdrivers, nut drivers, and basic hand tools
• Replacement inducer motor or capacitor if needed
• Shop vacuum or brush for clearing ducts/terminations

Estimated Costs And Timeframes

Costs vary by region and whether a technician is used. Expect the following ballpark ranges: Pressure switch replacement $80–$200 parts and labor; Inducer motor replacement $250–$600; Minor tubing or cleaning fixes $50–$150. DIY repairs reduce cost to parts only. Typical service call with diagnosis usually takes 1–2 hours; inducer or switch replacements may take 1–3 hours for a trained technician.

When To Call A Professional

Call a licensed HVAC technician if the problem involves gas line work, heat exchanger inspection/repair, unclear electrical issues, or if initial troubleshooting does not resolve the issue. Repeated lockouts, visible corrosion, or suspected heat exchanger cracks are serious safety concerns requiring professional attention.

Preventive Maintenance To Avoid Pressure Switch Failures

Regular maintenance reduces the chance of combustion air switch issues. Recommended steps include annual furnace tune-ups, cleaning inducer housings and terminations, inspecting and replacing pressure tubing during service, checking vent routing, and ensuring intake/exhaust terminations remain clear year-round.

Safety Considerations And Regulatory Notes

Working on gas furnaces carries risk. Never bypass safety switches or short the pressure switch to force the furnace to run; this creates hazardous conditions. Follow local codes and manufacturer guidance. In many jurisdictions, major gas appliance repairs must be performed or inspected by a licensed professional.

Model-Specific Considerations For Coleman Furnaces

Coleman furnace models may use different pressure switch setpoints and inducer assemblies. Always reference the model’s data plate and wiring diagram. Some units use dual pressure switches or integrated control modules; diagnosing requires understanding the specific control logic used by the model. OEM replacement parts ensure compatibility and proper safety ratings.

Quick Troubleshooting Checklist

1. Record furnace error codes and LED patterns.
2. Inspect and clear outside intake and exhaust terminals.
3. Verify inducer motor runs and sounds normal.
4. Check all pressure tubing for leaks or damage.
5. Test pressure switch continuity with multimeter during inducer operation.
6. Measure inducer vacuum with a manometer against switch specs.
7. Inspect wiring and control board terminals for corrosion or looseness.
8. Call a licensed technician for heat exchanger concerns or gas-related repairs.

Frequently Asked Questions

Can A Homeowner Replace A Pressure Switch?

Yes, many homeowners can replace a pressure switch if comfortable with basic electrical work and the furnace is powered down. Ensure the replacement switch matches model specs. If in doubt, hire a technician.

Is It Safe To Bridge The Pressure Switch To Run The Furnace?

No. Bridging or bypassing safety switches is dangerous and illegal in many areas. It allows the furnace to operate without proper airflow verification, risking unburned gas and carbon monoxide hazards.

How Long Does A Pressure Switch Last?

Pressure switches can last many years but wear, corrosion, or mechanical failures can occur. Regular maintenance and keeping tubing clean extend service life.

Useful Links And Resources

For model-specific diagrams and part numbers, consult the Coleman furnace manual and the equipment data plate. For safety and building codes, refer to local building departments and the National Fuel Gas Code (NFPA 54). When in doubt, contact a licensed HVAC contractor or the manufacturer’s technical support for guidance.

Addressing a Coleman furnace combustion air switch that won’t close requires methodical troubleshooting focused on airflow, inducer performance, tubing integrity, and switch function. Following the steps outlined helps identify the root cause and determine whether a DIY fix or professional service is appropriate.