Error code reference

Carrier Furnace Error Code 43

Low-heat pressure, draft safeguard (when used), or auxiliary limit switch (when used) open while high-heat…

Low-heat pressure, draft safeguard (when used), or auxiliary limit switch (when used) open while high-heat pressure switch is closed.

First step from the service manual

Check for pressure switch stuck open, disconnected or obstructed pressure tubing; refer to codes 32 and 33.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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Step-by-step tests with expected resistance, voltage, and continuity values
Wiring diagram references and connector pinouts from the OEM service manual
Verified part numbers when replacement is required

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M+ Max·Carrier furnace

43 on my Carrier furnace

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Low-heat pressure, draft safeguard (when used)

From Service Manual 102553, p.45:

1.Check for pressure switch stuck open, disconnected or obstructed pressure tubing; refer to codes 32 and 33.

2.Measure control board supply voltage at the test points. Expected: 12 VDC and 5 VDC; a drop below 4.75 VDC on the logic rail points to a failed onboard regulator.

3.Inspect all connectors on the main control for corrosion, thermal stress, or backed-out pins. Reseat each connector with the power disconnected.

Part WPW10804018

Electronic control board

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First step from the service manual

Get the full diagnostic procedure for 43.

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