Outdoor condensing unit with a large fan on a steel stand
Generic photo: ready made · Pexels License

Heat pump blows cold in heat mode (or heats in cool mode)

The reversing valve is in the wrong position. Check the thermostat O/B setting first, then 24 V at the solenoid coil, then the coil itself. A valve that won't shift with a good energized coil is sealed-system work.

Cross-checked ~30 min moderateBrands: All

Before you start

  • Outdoor unit has line voltage: keep probes on the 24 V coil leads only, or power off before handling.

Diagnostic steps

Unlock all 5 steps with expected values

Full library + AI assistant for $34.90, one time.

Get lifetime access

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work.

More air conditioners guides

Guide · Air Conditioner

PTAC not cooling (fan runs, air not cold)

Most PTAC no-cool calls are airflow (filter, coils), a wrong control setting or a failed compressor start component. Rule those out before suspecting the sealed system.

6 steps ~60 minmoderate
Guide · Air Conditioner

PTAC not heating (electric heat or heat pump)

PTACs heat with electric strip heat, a heat pump, or both. Heat pump models switch to strip heat in cold weather. Check settings, then the heater element and its limits, then the reversing valve.

5 steps ~60 minmoderate
Guide · Air Conditioner

PTAC error codes: how to read and clear them

Most PTAC brands store fault codes that can be shown with a button combination on the control (for example GE Zoneline uses a MODE + another key sequence on some models). Read the active code, fix the cause, then clear it.

4 steps ~20 mineasy
Heat pump blows cold in heat mode (or heats in cool mode) · OnCall Tech