Payne packaged AC unit shows F1 on its display; unit may not start cooling.

Safety: Disconnect power to the packaged unit before removing any panels.

• 1. Locate the sensor: On many Payne packaged units, the indoor temperature sensor (thermistor) is mounted in the return air stream or on the control board harness. Refer to the wiring diagram on the access panel.
• 2. Inspect connections: Ensure the thermistor plug is fully seated on the control board and that the wires are not pinched or cut.
• 3. Visual check of sensor: Look for physical damage, corrosion, or signs of overheating on the sensor body.
• 4. Reset power: After reseating connections, restore power and see if F1 clears.
• 5. Sensor replacement: If the code persists, the thermistor is likely out of range and should be replaced with the correct Payne part. This is a low-voltage component and can often be replaced by a careful DIYer following the service manual.