mypros+
Error code reference

Goodman Air Conditioner Error Code F1

Indoor Ambient Thermistor reads outside the range -20°F to 200°F and the wireless thermostat is not…

Goodman codesGoodman air conditioner codes

Indoor Ambient Thermistor reads outside the range -20°F to 200°F and the wireless thermostat is not communicating, or IAT without wireless remote thermostat reads outside the range -20°F to 200°F.

First step from the service manual

Replace black Indoor Ambient Thermistor or Wireless Remote Thermostat.

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

MyPros+ Max

Get the full diagnostic procedure for F1.

  • 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
Get the full procedure

$29/month · Cancel anytime · Or $9.95 3-day pass

What F1 means on a Goodman air conditioner

The F1 error code on a Goodman air conditioner indicates that the Indoor Ambient Thermistor (IAT) is reading a temperature value outside the accepted operating range of -20°F to 200°F. This fault triggers under two distinct conditions: either the system is equipped with a wireless remote thermostat that has lost communication with the indoor unit while the IAT reads out of range, or the IAT is operating without a wireless remote thermostat and is producing a signal that falls outside the valid range. The IAT is a black thermistor sensor responsible for measuring the ambient air temperature inside the conditioned space and feeding that data to the control board.

When the thermistor resistance drifts outside the range corresponding to -20°F to 200°F, the control board interprets the signal as either an open circuit, a short circuit, or a failed sensor. A thermistor that has developed an open circuit will typically send a resistance value that the board reads as an extreme low temperature, while a shorted thermistor will produce a resistance reading interpreted as an extreme high temperature. Either condition causes the board to flag F1 and suspend normal operation to prevent erroneous temperature-based control decisions.

In systems using wireless communication, the F1 code can also appear when the wireless remote thermostat drops its connection to the indoor unit simultaneously with an IAT fault. In this scenario, the control board loses two sources of temperature reference at once. Diagnosing F1 requires checking the thermistor's resistance with a multimeter, inspecting wiring harness connections at the control board, and verifying wireless thermostat signal strength and battery condition if applicable.

Source: manufacturer service documentation.

Common causes of F1

  1. 01

    Failed Indoor Ambient Thermistor

    Part replacement

    The black IAT sensor has developed an open or short circuit, causing its resistance to fall outside the range the control board accepts. Confirm by measuring the thermistor resistance with a multimeter and comparing it to the expected value at a known room temperature.

  2. 02

    Loose or damaged thermistor wiring connection

    Wiring / connection

    The connector between the IAT and the control board may have come loose, corroded, or suffered wire damage, causing an intermittent or fully open circuit. Inspect the wiring harness and connector pins for corrosion, bent terminals, or disconnection.

  3. 03

    Wireless remote thermostat communication failure

    Wiring / connection

    In wireless-equipped systems, the remote thermostat may have lost its radio link to the indoor unit due to low batteries, excessive range, or interference. Check thermostat battery condition and verify the unit is within communication range.

  4. 04

    Failed wireless remote thermostat

    Part replacement

    The wireless thermostat itself may have a hardware fault preventing it from communicating, even after battery replacement and repositioning. If communication cannot be restored after troubleshooting, the thermostat likely requires replacement.

  5. 05

    Control board input circuit fault

    Part replacement

    In rare cases the thermistor input circuit on the control board may be damaged, causing it to misread a functioning sensor as out of range. This is typically suspected only after confirming the thermistor and wiring test correctly.

See the test procedure for each cause

Frequently asked questions about F1

What does F1 mean on a Goodman air conditioner?
F1 on a Goodman air conditioner means the Indoor Ambient Thermistor is reading a temperature outside the valid range of -20°F to 200°F. This indicates the sensor may be faulty, disconnected, or shorted. On systems with a wireless thermostat, a simultaneous loss of communication with that thermostat can also trigger this code. The system flags F1 to prevent it from making control decisions based on an invalid temperature reading.
Can I fix the F1 error code myself?
A knowledgeable DIYer can inspect the thermistor wiring connections and check wireless thermostat batteries without special tools. If the wiring looks intact, testing the black IAT sensor with a multimeter to check its resistance can confirm whether it has failed. Replacing the thermistor or wireless thermostat is a straightforward repair, but if the control board is suspected, professional diagnosis is recommended.
Will resetting the Goodman air conditioner clear the F1 code?
A power reset may temporarily clear the F1 code, but it will return if the underlying fault with the thermistor or wireless thermostat has not been corrected. Resetting the unit does not fix a failed sensor or a broken communication link. The fault must be diagnosed and repaired to permanently resolve the code.
Is it safe to run my Goodman air conditioner with an F1 error?
Operating the system while F1 is active is not advisable because the control board lacks a reliable indoor temperature reference. Without accurate ambient temperature data, the system cannot make correct decisions about heating or cooling cycles. Continued operation could result in inefficient performance or improper control responses.
How much does it cost to fix a Goodman F1 error code?
If only the Indoor Ambient Thermistor needs replacement, parts and labor typically fall in the range of $75 to $200 depending on the technician's rates and your location. A wireless remote thermostat replacement can range from $100 to $300 or more, depending on the specific model required. If the control board is at fault, repair costs can be considerably higher, generally in the range of $250 to $600 or more.

Related Goodman air conditioner codes

All Goodman air conditioner codes
View all 27 Goodman air conditioner codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass