High-efficiency condensing furnaces, which produce significant condensation, often have their pressure switch located lower on the unit to accommodate the drainage systems associated with the secondary heat exchanger. It is usually mounted near the top of the unit, close to where the inducer motor is located.
Typical Pressure Switch Location by Furnace Type
In older units, the pressure switch might be mounted vertically on the combustion chamber or located near the bottom of the unit. One tube runs to the inducer motor to sense the pressure, while the other is vented to the outside or to the heat exchanger to compare the actual pressure against a set threshold.
Furnace Type Typical Pressure Switch Location Number of Tubes Standard Efficiency (80% AFUE) Top or side of the blower compartment Two (Inducer and Venting) High Efficiency (90%+ AFUE) Lower front or side of the unit Three (Inducer, Venting, and Drain) Old/Masonry Furnaces Near the combustion chamber or rear One or Two Common Issues Related to the Switch Because the pressure switch is directly linked to the inducer motor and the venting system, issues often stem from related components rather than the switch itself. The tubing is usually clear or black plastic and can sometimes be brittle, so handling the component requires care to avoid cracking the ports.
Typical Pressure Switch Location for Different Furnace Types
If the switch detects that the pressure is too low—indicating a blockage, a leak in the venting, or a failing inducer motor—it will open the circuit, cutting power to the system and preventing a potential build-up of toxic gases like carbon monoxide. Understanding the Role of the Pressure Switch The pressure switch is not a component that generates heat or directly controls the flame; rather, it is a safety sensor.
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