Air-source heat pump outdoor unit beside a house in the snow
Generic photo: PeterEastern · CC BY-SA 4.0

Mini-split not heating (blows cold, no air, or weak heat in HEAT mode)

Two normal behaviors cause many 'no heat' calls: the hot-start delay (the indoor fan stays off until the coil is warm) and defrost (the outdoor coil is cleared of frost, and the indoor unit stops heating for several minutes). Rule those out, then check mode and set point, filters, the outdoor unit, power and any error code. Reversing-valve and refrigerant problems are diagnosis-and-refer.

Cross-checked ~30 min easyBrands: All ductless brands

Before you start

  • Turn the unit off before clearing snow or debris; do not chip ice off the outdoor coil with tools or spray water into the cabinet
  • Inverter boards hold high DC voltage after power-off; do not open the outdoor unit electrical box unless trained
  • No refrigerant work: suspected low charge or reversing valve faults go to an EPA 608 certified technician

Diagnostic steps

Unlock all 6 steps with expected values

Full library + AI assistant + the OnCall Tech app for iPhone & Android. $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, on GE Zoneline (2019 technical service guide) you hold FAN and the red AUX button together while the unit is OFF, and AUX clears stored faults; other models use other sequences, so use the model's tech sheet). Read the active code, fix the cause, then clear it.

4 steps ~20 mineasy
Mini-split not heating (blows cold, no air, or weak heat in HEAT mode) · OnCall Tech