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Error code reference

Goodman Air Conditioner Error Code F3

Indoor Ambient Thermistor reads outside the range -20°F to 200°F.

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Indoor Ambient Thermistor reads outside the range -20°F to 200°F.

First step from the service manual

Replace black Indoor Ambient Thermistor.

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
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What F3 means on a Goodman air conditioner

The F3 error code on a Goodman air conditioner indicates that the Indoor Ambient Thermistor is reading a temperature value outside the acceptable operating range of -20°F to 200°F. The indoor ambient thermistor is a small negative temperature coefficient (NTC) sensor that monitors the air temperature inside the conditioned space. The control board uses this reading to make decisions about system operation, and when the value falls outside the defined window, the system flags the fault to prevent operating on faulty data.

The most direct cause of this fault is a failed thermistor itself. Thermistors degrade over time due to heat cycling, moisture exposure, or physical damage, causing their resistance to drift far outside the expected range. A shorted thermistor will report an abnormally high temperature, while an open circuit will report an abnormally low or nonsensical value. Either condition will trigger the F3 code. The thermistor is identified by its black housing and connects directly to the main control board via a low-voltage wiring harness.

Wiring and connection issues can also produce this fault without the sensor itself being defective. A loose or corroded connector at the thermistor or at the control board input can cause intermittent or out-of-range readings. Before condemning the thermistor, it is worth inspecting the connector pins and wiring for damage, corrosion, or a pulled terminal. However, given the straightforward nature of this fault and the low cost of the thermistor, replacement of the black indoor ambient thermistor is the recommended first diagnostic action.

Source: manufacturer service documentation.

Common causes of F3

  1. 01

    Failed Indoor Ambient Thermistor

    Part replacement

    The black indoor ambient thermistor has degraded or failed outright, causing it to report a resistance value that corresponds to a temperature outside the -20°F to 200°F range. This is the most common cause and replacement of the thermistor is the recommended first step.

  2. 02

    Open Circuit in Thermistor Wiring

    Wiring / connection

    A broken wire in the low-voltage harness connecting the thermistor to the control board can cause the board to read an open circuit, which registers as an out-of-range temperature value. Inspect the wiring from the thermistor back to the control board for any visible breaks or damage.

  3. 03

    Loose or Corroded Connector

    Wiring / connection

    A loose, corroded, or poorly seated connector at the thermistor plug or at the control board header can cause intermittent or invalid readings that trigger the F3 fault. Check the connector pins for corrosion, bent terminals, or a connector that has partially backed out of its housing.

  4. 04

    Shorted Thermistor

    Part replacement

    A shorted thermistor causes the control board to read an extremely high temperature far above 200°F, triggering the F3 code. Shorts can occur due to moisture intrusion or insulation breakdown in the sensor body.

  5. 05

    Control Board Input Circuit Fault

    Part replacement

    In rare cases, the thermistor itself tests within normal resistance specifications but the control board input circuit that reads the sensor signal has failed. This is the least common cause and should only be considered after the thermistor and wiring have been confirmed good.

See the test procedure for each cause

Frequently asked questions about F3

What does F3 mean on a Goodman air_conditioner?
The F3 code on a Goodman air conditioner means the Indoor Ambient Thermistor is reading a temperature value outside the valid range of -20°F to 200°F. The control board uses this sensor to monitor indoor air temperature, and when the reading falls outside that range, the system triggers the fault. The thermistor is identified by its black housing and connects to the control board via a low-voltage wiring harness. A failed sensor is the most likely cause.
How do I fix the F3 error on my Goodman air conditioner?
The recommended first step is to replace the black Indoor Ambient Thermistor. Before replacing it, inspect the wiring harness and connector at both the thermistor and the control board for any loose pins, broken wires, or corrosion, since a wiring issue can produce the same fault without the sensor being defective. If the wiring checks out and the fault persists after thermistor replacement, the control board input circuit may need evaluation.
Is it safe to run my Goodman air conditioner with an F3 error?
Operating the unit with an active F3 fault is not recommended. The control board cannot accurately monitor indoor conditions without a valid thermistor reading, which may cause the system to operate incorrectly or prevent it from running at all. Continued operation in this state can potentially mask other developing issues, so the fault should be diagnosed and corrected promptly.
Will resetting the unit clear the F3 error code?
A power reset may temporarily clear the F3 code from the display, but the fault will return if the underlying cause has not been addressed. If the thermistor is failed, open, or shorted, the control board will detect the out-of-range reading again as soon as it checks the sensor input. A lasting repair requires replacing the thermistor or correcting the wiring fault.
How much does it cost to repair a Goodman F3 error code?
Repair costs depend on what component has failed. If only the Indoor Ambient Thermistor needs replacement, the part itself is generally inexpensive, typically in the range of $10 to $40, and labor for a straightforward thermistor swap is usually on the lower end of a service call charge. If the fault turns out to involve the control board, total repair costs can range from $200 to $600 or more depending on the board and labor rates in your area.

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