The Goodman furnace pressure switch is a safety device that confirms proper venting and draft before ignition. Located near the inducer, it senses negative pressure in the vent path to ensure safe combustion. If the switch doesn’t close, the furnace will not ignite to prevent potentially dangerous conditions. Understanding where this switch sits and how it functions can help homeowners troubleshoot common ignition issues and decide when to call a technician.
What Is A Pressure Switch On A Goodman Furnace
A pressure switch is a small device on the inducer assembly that monitors the vent system’s draft. It uses a vacuum line to sense when the inducer fan creates sufficient negative pressure to safely exhaust combustion gases. The switch is wired into the furnace control board and must close to allow the ignition sequence to proceed. If the switch fails or cannot sense proper draft, the control board typically stops ignition and may display a fault code.
In Goodman systems, the pressure switch works with the inducer motor and limit controls to verify that exhaust flow is clear before gas is released. Any obstruction, misrouting of hoses, or cracked tubing can cause false readings, preventing ignition even when ignition components are ready. Proper operation depends on a clear, unobstructed vacuum path from the inducer to the switch.
Typical Locations On Goodman Models
On most Goodman furnaces, the pressure switch sits adjacent to the inducer housing, often near the top or side of the blower cabinet. Two small vacuum hoses connect the inducer to the switch, and some models route a third line to the combustion chamber. The switch itself is a compact component with electrical terminals that connect to the furnace control board. While the exact placement varies by model, locating the inducer assembly will usually reveal the pressure switch.
- Inducer housing area at the top or side of the furnace cabinet
- Two small vacuum hoses running from the inducer to the switch
- Electrical pigtail or terminal block feeding the switch to the control board
- Nearby access panel may expose the switch during service
Some Goodman models, especially newer GMVC or GSZ series units, integrate the pressure switch with the inducer assembly in a single module. In these cases, replacement or testing often involves removing or accessing the inducer housing rather than a separate, standalone switch.
How To Locate The Pressure Switch Safely
- Power off the furnace and shut off the gas supply if accessible. Remove the front panel to access the burner area. Wait a few minutes for any residual energy to dissipate.
- Identify the inducer assembly at the top of the furnace. Look for two small flexible hoses that connect to a tiny switch mounted on or near the inducer.
- Trace the vacuum lines carefully. Do not kink or pinch hoses, and avoid forcing components through tight openings, which can cause future leaks.
- Spot the pressure switch itself, typically a small round or square device with electrical terminals. It will have two or more wires connected to the furnace control board.
- Take note of model-specific layouts in the user manual or service guide before removing any components. If uncertain, consult a professional technician to avoid miswiring or gas-related hazards.
- When reassembling, ensure all hoses are securely attached and the access panel is properly sealed to prevent air leaks.
Signs Of A Faulty Pressure Switch
- The furnace fails to ignite or repeatedly enters a lockout sequence without showing a clear ignition sequence.
- Unusual furnace cycling, such as frequent on/off or extended pre-ignition delays, with no flame established.
- Fault codes related to draft, venting, or inducer problems on the control board.
- Visible cracked or kinked vacuum hoses, loose connections, or corrosion at the switch terminals.
- Unexplained leaks or obstructions in the inducer path or clogged condensate lines affecting venting.
Note: A faulty pressure switch can mimic other ignition faults. Do not bypass the switch, as this removes a critical safety function and can create unsafe conditions.
How To Test The Pressure Switch
Testing should be done with caution. If you are not comfortable working with gas appliances, contact a licensed HVAC technician. The following steps outline safe, common testing methods used by professionals.
Using A Vacuum Pump To Test
With power off, disconnect the vacuum hose from the pressure switch. Attach a handheld vacuum pump and apply a small, steady vacuum (typically around 0.5 to 1 inch of water, depending on the model). The switch should close as vacuum is applied and reopen when the vacuum is released. If the switch does not respond, it may be defective or the line may be blocked.
Electrical Continuity Check
With the vacuum hose reattached, carefully disconnect the switch’s wiring harness from the control board. Use a multimeter set to continuity to verify that the switch closes when vacuum is present and opens when vacuum is removed. A lack of proper continuity under the test conditions indicates a faulty switch or a compromised connection.
Post-test steps include reconnecting the harness securely, reattaching hoses, and powering the furnace back on to observe normal operation. If ignition still fails, inspect the inducer for obstruction, inspect vent paths for blockages, and verify the control board for error codes.
Common Replacement Considerations And Safety
- Use an OEM or manufacturer-approved pressure switch compatible with the specific Goodman model to ensure proper fit and electrical ratings.
- Before replacement, verify that venting paths are clear and there are no exhaust leaks that could affect readings.
- When installing a new switch, attach vacuum lines and electrical connections firmly without over-torquing terminals or hoses.
- After replacement, test the system with a vacuum pump and continuity check, then attempt a soft ignition to confirm proper operation.
- Never bypass a pressure switch. Bypassing eliminates a critical safety feature and can lead to gas buildup or carbon monoxide exposure.
Additional Tips For Different Goodman Series
Goodman models vary in how the pressure switch is presented. On many GMVC and GSZ models, the switch is integrated into the inducer module, making replacement more involved. In simpler, earlier Goodman furnaces, the switch is a discrete component with a direct hose connection and a straightforward electrical connector. In all cases, ensure that the vent system is completely clear and that there are no cracks in hoses or the inducer housing. Consult the model-specific service manual for exact locations and torque specifications to avoid damage.