Why does my air conditioning blow cold air in winter?

You expect heat.
Cold air comes out instead.
Winter comfort disappears.

This is one of the most common winter complaints from air conditioning users. In most homes, the system is not broken. It is reacting to settings, protection cycles, or normal winter behaviour.

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Cold air does not always mean cooling

Cold air during winter does not automatically mean the system is cooling.

Air conditioning systems manage
Temperature
Airflow
Internal protection

During heating, short periods of cool or neutral air can occur. These are often mistaken for faults.

Understanding when cold air is normal avoids unnecessary call outs.

The most common cause is the wrong mode

Mode selection causes most winter cold air issues.

If the system is in cooling mode, it will cool regardless of the temperature setting. If it is in auto mode, it may switch behaviour based on sensor readings.

Always confirm the controller shows
The word HEAT
A sun symbol

Without this, heating is not locked in.

Cold air during start up is normal

When heating is first selected, the system protects itself.

It may
Delay airflow
Run the fan slowly
Blow neutral or cool air briefly

This prevents cold drafts once the heating coil starts warming.

This phase usually lasts a few minutes.

Defrost cycles cause temporary cold air

In cold weather, outdoor units collect frost.

To remove it, the system enters a defrost cycle. During defrost
Indoor heating pauses
Airflow may continue
Air can feel cool

This is normal winter behaviour. Heating resumes automatically once defrost completes.

Auto mode causes unexpected cooling

Auto mode allows the system to decide whether to heat or cool.

Small temperature changes near the sensor can trigger cooling even in winter. Sunlight, cooking, or people in the room often cause this.

Auto mode is one of the biggest causes of cold air complaints.

For winter use, heating mode gives more predictable results.

Fan only mode feels like cold air

Fan only mode circulates room air.

It does not heat or cool.
In winter, this air feels cold.

Fan only mode is often selected accidentally when cycling through modes.

If you see a fan symbol without HEAT, the system is not heating.

Fan speed affects how cold air feels

Fan speed changes sensation.

High fan speed moves air quickly and increases heat loss from your body. Even warm air can feel cool when it moves fast.

Medium fan speed usually feels warmer and more comfortable during heating.

Standing near the unit exaggerates the problem

Airflow near the unit does not reflect room temperature.

Standing directly under or in front of the unit makes air feel cooler due to movement, not temperature. This leads users to believe cold air is being produced when the room is actually warming.

Judge comfort from the centre of the room.

Common winter settings that cause cold airflow

These appear frequently during support visits.

Cooling mode left active
Auto mode enabled
Fan only mode selected
High fan speed used immediately
Timers changing behaviour
Multiple controllers sending commands

Checking these resolves most issues.

When cold air points to a real issue

Cold air may indicate a problem if it continues well beyond normal behaviour.

Possible causes include
Sensor faults
System sized mainly for cooling
Restricted airflow
Installation related issues

These require assessment.

When to seek professional support

Contact a specialist if
Heating mode is confirmed and cold air persists beyond 15 minutes
Error codes appear
The outdoor unit does not operate
The system shuts down repeatedly

Before calling, note the mode, fan speed, outdoor temperature, and how long the issue has been happening.

This speeds up diagnosis.

Related guidance

Further residential air conditioning guidance is available at
https://www.climateworks.co.uk/residential-air-conditioning

References

UK Government guidance on heat pump operation
https://www.gov.uk/guidance/heat-pumps-how-they-work

Building Regulations Approved Document L
https://www.gov.uk/government/publications/conservation-of-fuel-and-power-approved-document-l

ClimateWorks residential service records from installations across Hampshire, Berkshire, Surrey, and Oxfordshire between 2022 and 2025

Author

Dr Julian Carter
Technical and Compliance Director
ClimateWorks

Dr Julian Carter has over 20 years of experience in building services engineering, air conditioning system design, and regulatory compliance. He advises on residential and commercial projects across the UK, covering system selection, installation standards, commissioning, and real world performance.

As Technical and Compliance Director at ClimateWorks, he oversees technical governance, installer training, fault diagnosis, and customer education. His work focuses on reducing user related issues, improving system reliability, and ensuring air conditioning systems perform consistently throughout their service life.

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