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Error code reference

Goodman Air Conditioner Error Code F4

Indoor Coil Thermistor either above or below operating tolerances.

Goodman codesGoodman air conditioner codes

Indoor Coil Thermistor either above or below operating tolerances.

First step from the service manual

Replace Red Indoor Coil 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
  • Wiring diagram references and connector pinouts from the OEM service manual
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What F4 means on a Goodman air conditioner

The F4 error code on a Goodman air conditioner indicates that the indoor coil thermistor has reported a temperature reading that falls either above or below the accepted operating tolerances for the system. The indoor coil thermistor is a temperature-sensing resistor positioned on or near the evaporator coil inside the air handler. It continuously monitors coil temperature and feeds that data to the control board, which uses it to manage defrost cycles, refrigerant flow decisions, and system protection logic. When the signal from this thermistor drifts outside the expected range, the control board interprets it as a fault and triggers F4.

The red indoor coil thermistor is identified by its red lead wires and is the specific component flagged in this fault. Thermistor failures typically present in two ways: the resistance value climbs too high (indicating a cold or open sensor) or drops too low (indicating an overheated or shorted sensor). Either condition causes the control board to receive inaccurate coil temperature data, which can lead to improper system operation or a protective shutdown.

Common root causes include a failed thermistor element, a damaged or corroded connector at the thermistor harness, or wiring that has been pinched or abraded. In some cases, the thermistor may be physically dislodged from its mounting clip on the coil, causing it to read ambient air temperature rather than actual coil temperature. The first recommended diagnostic action is direct replacement of the red indoor coil thermistor, as this component is relatively inexpensive and the failure mode is straightforward to confirm.

Source: manufacturer service documentation.

Common causes of F4

  1. 01

    Failed Indoor Coil Thermistor

    Part replacement

    The red indoor coil thermistor itself has degraded or failed, causing its resistance output to fall outside acceptable operating tolerances. This is the most common cause and is confirmed by removing and testing the thermistor resistance against the expected value for the current temperature.

  2. 02

    Dislodged Thermistor from Mounting Clip

    Wiring / connection

    If the thermistor has slipped out of its clip on the evaporator coil, it will read ambient air temperature instead of coil temperature, producing an out-of-range signal. Visually inspect the thermistor position on the coil to confirm it is properly seated.

  3. 03

    Damaged or Corroded Thermistor Connector

    Wiring / connection

    Moisture, corrosion, or physical damage at the wiring harness connector can interrupt or distort the thermistor signal to the control board. Inspect the connector pins for oxidation, debris, or bent contacts and clean or replace as needed.

  4. 04

    Pinched or Abraded Thermistor Wiring

    Part replacement

    The wiring between the thermistor and the control board may have been pinched during installation or worn through over time, creating an intermittent or short circuit condition. Trace the wire run and look for visible damage or contact with sharp sheet metal edges.

  5. 05

    Faulty Control Board

    Part replacement

    If the thermistor and all associated wiring test within acceptable parameters but the F4 fault persists, the control board's thermistor input circuit may have failed. This is the least likely cause and should only be considered after the thermistor and wiring have been ruled out.

See the test procedure for each cause

Frequently asked questions about F4

What does F4 mean on a Goodman air_conditioner?
The F4 code means the indoor coil thermistor has reported a temperature reading that is either too high or too low compared to the system's accepted operating tolerances. The indoor coil thermistor, identified by its red leads, monitors the evaporator coil temperature and sends that data to the control board. When the signal falls out of range, the control board logs F4 to alert the technician. The first recommended step is to replace the red indoor coil thermistor.
Can I fix the F4 error code myself?
A knowledgeable DIYer can inspect the thermistor for physical damage, check that it is properly seated in its mounting clip on the coil, and examine the wiring connector for corrosion. Replacing the thermistor itself is a relatively straightforward task if you are comfortable working inside the air handler. However, if the fault persists after thermistor replacement, diagnosing the control board or wiring requires more advanced skills and a multimeter.
Is it safe to run my Goodman air conditioner with an F4 error?
Running the system while F4 is active is not recommended. The control board relies on accurate coil temperature data from the thermistor to manage system operation and protection functions. Without a reliable temperature reading, the unit may operate improperly, potentially leading to issues like coil icing or insufficient compressor protection. It is best to address the fault before continuing normal operation.
How much does it cost to repair an F4 error on a Goodman air conditioner?
If only the indoor coil thermistor needs replacement, the repair is typically among the more affordable fixes, with parts costs generally ranging from around $10 to $50 and labor costs varying by region and technician. If the fault turns out to involve the control board, repair costs can range considerably higher, from $150 to $600 or more depending on parts and labor. Getting a diagnostic visit from a qualified technician will give you a clearer cost estimate for your specific situation.
Will resetting the Goodman air conditioner clear the F4 error code?
A power reset may temporarily clear the F4 code, but if the underlying thermistor problem is still present, the fault will return once the system runs through its diagnostics again. Resetting without addressing the faulty thermistor or wiring is not a lasting solution. The root cause needs to be identified and corrected to prevent the code from recurring.

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