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Error code reference

Goodman Heat Pump Error Code A3

Outdoor coil temperature sensor fault

Goodman codesGoodman heat pump codes

Outdoor coil temperature sensor fault - shorted, open, disconnected, or out of range sensor.

First step from the service manual

Check sensor connection. Replace open/shorted sensor.

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

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  • Wiring diagram references and connector pinouts from the OEM service manual
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What A3 means on a Goodman heat pump

The A3 error code on a Goodman heat pump indicates a fault with the outdoor coil temperature sensor, also called the outdoor coil thermistor. This sensor monitors the refrigerant-side temperature of the outdoor heat exchanger coil, providing critical feedback to the control board for defrost cycle management and system protection. When the control board detects a signal that falls outside the expected resistance range for the sensor, or detects an open or short circuit in the sensor circuit, it triggers the A3 fault.

Thermistors used in these applications are NTC (negative temperature coefficient) devices, meaning their resistance decreases as temperature rises. The control board expects a specific resistance range corresponding to operating temperatures. A shorted sensor produces abnormally low resistance, while an open sensor or disconnected wiring produces infinite or no resistance. Either condition causes the board to flag the circuit as faulty and log the A3 code.

The most common physical causes include a sensor connector that has worked loose from vibration, corrosion on the connector pins causing increased resistance or intermittent contact, physical damage to the sensor wire from rubbing against the coil or cabinet edges, and outright sensor failure due to age or moisture intrusion. Because this sensor directly influences defrost timing, an unresolved A3 fault can cause the outdoor coil to ice over or prevent proper defrost cycles, reducing system efficiency and potentially causing compressor damage over time.

Source: manufacturer service documentation.

Common causes of A3

  1. 01

    Loose or disconnected sensor connector

    Wiring / connection

    Vibration during normal operation can cause the sensor's wiring harness connector to loosen or pull free from its socket on the control board or sensor body. Inspect the connector at both ends and reseat it firmly.

  2. 02

    Corroded or damaged connector pins

    Wiring / connection

    Moisture exposure in the outdoor unit can cause oxidation on the connector pins, increasing resistance and producing out-of-range readings. Look for green or white buildup on the pins and clean or replace the connector as needed.

  3. 03

    Failed outdoor coil thermistor

    Part replacement

    The sensor itself can fail due to age, physical damage, or moisture intrusion into the sensor body. An open or shorted thermistor will not self-recover and must be replaced.

  4. 04

    Damaged sensor wiring

    Part replacement

    The wire between the sensor and the control board can be chafed, pinched, or cut where it routes through or around the coil or cabinet panels. Inspect the full wire run for signs of insulation damage or breaks.

  5. 05

    Faulty control board

    Part replacement

    If the sensor and all wiring check out within normal resistance ranges and connections are secure, the control board's sensor input circuit may be defective. This is the least common cause and should be diagnosed only after ruling out the sensor and wiring.

See the test procedure for each cause

Frequently asked questions about A3

What does A3 mean on a Goodman heat_pump?
The A3 code indicates a fault with the outdoor coil temperature sensor. The control board has detected that the sensor circuit is shorted, open, disconnected, or producing a reading outside the expected range. This sensor is responsible for monitoring the outdoor heat exchanger coil temperature, which the system uses to manage defrost cycles and protect the equipment.
Can I fix the A3 error myself?
A homeowner with basic comfort around electrical connections can check whether the sensor connector is loose or unplugged, which is the most common cause and requires no parts or tools beyond a visual inspection. If the connector is secure and the error persists, diagnosing a failed thermistor or damaged wire requires a multimeter to check resistance values, and replacing the sensor involves working inside the outdoor unit. If you are not comfortable with that level of work, a licensed HVAC technician should handle it.
Is it safe to run my Goodman heat pump with an A3 fault active?
Running the unit with an active A3 fault is not recommended. The outdoor coil sensor directly controls defrost cycle timing, and without accurate sensor data the coil can accumulate ice, reducing efficiency and potentially overloading the compressor. Continued operation under these conditions can cause additional component failures that are more costly to repair.
How much does it cost to repair an A3 error on a Goodman heat pump?
If the fix is simply reseating a loose connector, there may be no parts cost, and a service call alone typically runs between 75 and 150 dollars depending on your area. Replacing the outdoor coil thermistor itself is a relatively inexpensive part, generally in the 20 to 60 dollar range, with total repair costs including labor often falling between 100 and 250 dollars. If the control board turns out to be the cause, board replacement is significantly more expensive, often ranging from 300 to 600 dollars or more with labor.
Will resetting the Goodman heat pump clear the A3 error code?
A power reset may temporarily clear the A3 code, but if the underlying sensor fault is still present the code will return once the control board re-checks the sensor circuit. A reset is useful for confirming whether a fault is intermittent, but it does not repair a failed sensor, damaged wire, or bad connection. The root cause must be corrected for the fault to clear permanently.

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