Furnace Pressure Switch Location and How to Find It

The furnace pressure switch location is a common search for homeowners diagnosing heating issues or preparing for repairs. This article explains where pressure switches are typically found, how they work, how to test them, and practical steps for safe access and replacement. It focuses on gas furnaces used in U.S. homes and provides troubleshooting guidance that helps determine whether the pressure switch is the cause of a no-heat condition.

Furnace Type	Common Pressure Switch Location	Notes
Single-Stage Condensing Furnace	Near inducer motor on the draft housing	Often uses PVC venting; switch connected by small vacuum tubing
Mid-Efficiency Furnace	On the blower or near combustion compartment	May be inside access panel or mounted to manifold
Older Non-Condensing Furnace	On flue collector box or near draft hood	Larger metal venting, tubing runs to switch

What Is A Furnace Pressure Switch And Why Its Location Matters

A furnace pressure switch is a safety device that confirms the inducer motor and vent system are drawing combustion gases correctly before ignition. The switch monitors negative pressure or vacuum created by the inducer motor; if the pressure is within a safe range, it signals the furnace control board to allow ignition. Proper placement near the inducer or draft housing ensures accurate pressure sensing and reliable operation.

How The Pressure Switch Works

The pressure switch contains a diaphragm that reacts to changes in pressure. When the inducer motor runs, it produces a slight negative pressure; this pulls the diaphragm closed and completes an electrical circuit. The control board senses the closed circuit and proceeds to the next stage of the heating sequence. If the diaphragm does not move, the furnace will lock out or display error codes to prevent unsafe ignition.

Common Pressure Switch Locations By Furnace Type

High-Efficiency Condensing Furnaces

On high-efficiency condensing furnaces, the pressure switch location is typically near the inducer motor or mounted on the draft housing. These units use PVC venting and the switch is connected by small flexible tubing to a pressure tap close to the inducer. The switch housing is often plastic and mounted externally for easy access.

Mid-Efficiency Furnaces

Mid-efficiency furnaces usually have the pressure switch installed on or near the combustion compartment. The switch may be mounted to the heat exchanger housing or on the blower plenum. Access often requires removing an access panel, and tubing connects the switch to a pressure port inside the furnace cabinet.

Older Non-Condensing Furnaces

Older furnaces that are non-condensing often place the pressure switch on the flue collector box or near the draft hood. These switches are typically metal-bodied and connected by tubing that senses pressure differences in the flue or draft area. Access may be more limited due to the design of older units.

How To Locate The Pressure Switch Step-by-Step

Turn off power to the furnace at the service switch or breaker before inspecting. Follow all safety precautions and never work on a furnace with power applied unless qualified to do so.

Remove the furnace access panel by loosening screws or clips. The pressure switch is generally visible near the inducer motor or draft assembly; look for a round or oval device with two electrical terminals and one or two small tubes attached.

Trace the small vacuum tubing from the switch; it often leads to a pressure tap or a nipple near the inducer or on the flue collector. The tubing is usually clear or black rubber and approximately 1/4 inch in diameter. Tracing the tubing is an effective way to confirm the exact pressure switch location.

Check the furnace manual or manufacturer wiring diagram inside the access panel. Many modern furnaces include a labeled schematic indicating the pressure switch location. The part number printed on the switch can also be referenced online for installation diagrams and technical specifications.

Visual Clues When Identifying The Pressure Switch

• Appearance: Round or oval switch with an electrical connector and 1/4″ vacuum tube.
• Mounting: Often screwed into the draft housing, near the inducer motor, or attached to the blower housing.
• Materials: Plastic-bodied on newer condensing units; metal or composite on older furnaces.
• Labeling: Marked with electrical ratings and a model number; may have arrows indicating pressure direction.

Testing The Pressure Switch Safely

Testing requires a multimeter and basic knowledge of furnace sequences. Maintain safety: turn off power before connecting or disconnecting components and follow manufacturer recommendations.

Check Continuity: With power off, disconnect the switch harness and use a multimeter set to continuity or ohms to test the switch. A closed circuit when the inducer runs indicates the switch is operating. If the switch is open when it should be closed, it may be stuck or defective.

Apply Vacuum: Use a hand-held vacuum pump to apply slight vacuum to the switch tube. If the switch closes at the specified vacuum level (usually 0.1–0.5″ wc depending on model), it is likely functional. If it does not close, the switch requires replacement.

Observe Operation: Power the furnace and watch the sequence. The inducer motor should start, creating a visible suction on the tubing. If the inducer runs but the pressure switch does not close, inspect tubing for clogs or disconnections and retest the switch.

Common Problems Related To Pressure Switch Location

Tubing Blockage: Debris, moisture, or rodents can clog the vacuum tubing from the pressure tap to the switch. Clogs prevent accurate pressure sensing and are a frequent cause of failure.

Loose Connections: The tubing may become disconnected at the switch or the pressure port. A disconnected tube results in an open circuit and a furnace lockout.

Corroded Switch: In older furnaces, corrosion or wear can cause the diaphragm to fail. Corrosion often occurs when the switch is mounted where condensate can collect or in areas with poor ventilation.

Poor Mounting: If the switch is mounted too far from the inducer or incorrectly grounded, it might read inaccurate pressure. Proper location relative to the inducer ensures reliable sensing.

Replacement And Access Considerations

Before replacing a pressure switch, verify the part number matches the furnace specifications. Manufacturers design switches with specific vacuum thresholds; mismatched parts can cause improper operation.

Replacement Steps: Turn off power and gas. Remove tubing and electrical connectors from the old switch. Note wiring orientation or photograph connections. Mount the new switch in the same location, attach tubing securely, and reconnect electrical terminals. Restore power and test operation through a heating call.

Professional Replacement: If the switch is inside a sealed compartment, involves complex wiring, or if the homeowner is not comfortable with electrical diagnostics, hiring a licensed HVAC technician is recommended. Proper calibration and safety checks are essential after replacement.

Troubleshooting Checklist For No-Heat Conditions Linked To Pressure Switch

1. Confirm inducer motor runs when the thermostat calls for heat.
2. Inspect vacuum tubing for cracks, kinks, or disconnects.
3. Check for blockages at the pressure tap and inside tubing.
4. Test switch continuity with a multimeter while inducer is running.
5. Use a vacuum pump to simulate inducer pressure and verify switch closure.
6. Inspect for error codes or LED blink patterns on the furnace control board indicative of pressure switch faults.

Safety Tips When Working Near The Pressure Switch

Always turn off power at the breaker or furnace switch before opening access panels. Never bypass a pressure switch; doing so can allow unsafe furnace operation and risk carbon monoxide exposure.

Wear appropriate PPE: safety goggles, gloves, and dust mask if the furnace area is dirty. Ensure proper ventilation when running the furnace for testing and never block vents or flues during diagnostics.

Use manufacturer-approved replacement parts. Improper components can cause hazardous operation or void warranties. When in doubt, consult a licensed HVAC technician for safe, code-compliant repairs.

When To Call A Professional

Call a licensed HVAC technician if the furnace displays repeated pressure switch faults after tubing and switch checks, if the inducer motor fails to run, or when flame rollout, unusual odors, or carbon monoxide alarms are present. Professionals have the tools and training to measure pressure accurately and diagnose venting or combustion safety issues.

Frequently Asked Questions About Furnace Pressure Switch Location

Can A Pressure Switch Be Relocated?

Relocation is generally not recommended because the switch must sense pressure at a specific point to function properly. Moving it can change the pressure characteristics and lead to false readings. Any relocation should follow manufacturer guidance.

How Much Does It Cost To Replace A Pressure Switch?

Part costs typically range from $20 to $100 depending on the brand and model. Labor costs vary by region; expect $100–$300 for professional replacement, depending on access complexity and diagnostic time.

Does A Pressure Switch Need Calibration?

Most pressure switches are factory-calibrated and sealed. Calibration is rarely adjustable in the field. If the switch does not operate at the correct vacuum level, replacement is usually the appropriate solution.

Key Takeaways For Locating And Servicing The Pressure Switch

Locate the switch near the inducer motor or draft housing, trace the small vacuum tubing, and consult the furnace manual for exact placement.

Inspect tubing and fittings first—most pressure switch problems result from tubing blockages or disconnections rather than a failed switch.

Test safely with a multimeter and vacuum pump; do not bypass safety devices.

Following these guidelines helps homeowners and technicians quickly find the furnace pressure switch location, diagnose common failures, and perform safe repairs that restore reliable heating performance. For complex issues or safety concerns, contact a licensed HVAC professional.