In winter many homes are heated with an air conditioner, so when your AC is not heating, the first thought is a fault. Often, though, the unit is simply warming up or clearing ice from the outdoor unit – a normal process. This guide explains why an AC may not heat, what you can check yourself and when you need a technician.

Why your AC is not heating – the main causes

According to official support pages from the air conditioner manufacturer Samsung, common causes of heating problems are:

  • Dirty air filters – dust on the filters reduces heating efficiency;
  • Temperature outside the operating range – if the indoor or outdoor temperature doesn’t match the allowed range for heating mode, the unit won’t perform well. The range is listed in your model’s manual;
  • Capacity doesn’t match the room size – a unit rated for a smaller area can’t heat the room enough;
  • Incorrect installation – Samsung says this kind of problem usually shows up within the first 3 months of active use after installation;
  • Low refrigerant (freon) – the refrigerant level should be checked by a technician or service engineer.

Source: Samsung – What to do if the air conditioner is not heating (official page, in Russian)

AC not heating – split system indoor and outdoor unit

Normal behaviour that looks like a fault

No warm air right after switching on

According to Samsung, for the first 3 to 5 minutes of heating mode the fan may not run – the unit warms up first so that it doesn’t blow cold air into the room. This is not a fault.

Heating stops and steam comes from the outdoor unit (defrost)

When it is cold and humid outside, frost can form on the outdoor heat exchanger and reduce heating efficiency. The unit then runs an automatic defrost function, which Samsung says lasts 5 to 12 minutes. During defrost the indoor unit stops so that no cold air comes out, and steam is produced at the outdoor unit. On Samsung units the display shows dF, and you can’t change other options with the remote until defrost has finished. Just wait – heating resumes on its own.

Weak heating in freezing weather

Samsung explains that an air conditioner takes heat energy from the outside air, so if the outdoor temperature is too low its heating ability may decrease. If the heat isn’t enough, use an additional heater together with the AC.

Source: Samsung UK – How do I use the heating mode on my air conditioner? (official page)

What you can check yourself

The steps below are based on Samsung’s recommendations and don’t require opening the unit:

1. Restart and give it time

Disconnect the AC from power for 1 minute, switch it back on and let it run for 5–7 minutes. If the unit hasn’t been used for a long time or was previously in cooling mode, give it 25–30 minutes – the system needs time to switch modes.

2. Check the mode and temperature on the remote

Press the Mode button until Heat is selected and set the highest temperature – usually +30°C. Make sure the indoor and outdoor temperatures are within the range given in your model’s manual.

3. Clean the filters

Samsung recommends cleaning the indoor unit’s air filters once every two weeks or more often. Your model’s manual explains how to remove and wash them.

4. Measure the outlet air temperature

In Heat mode at the maximum setting, after 5–7 minutes of running, hold a thermometer at the indoor unit’s air outlet for 30–40 seconds:

  • If the air coming out is at room temperature, or 5°C or more below the set temperature, the AC is not heating at all;
  • If it is close to the set temperature, the AC is heating but not enough for the room. Close windows and doors and check whether the unit’s capacity matches the room size.

When to call an AC technician

Checking and refilling freon, opening the units and repairing electronics are jobs for a technician. Call a professional if:

  • The AC still doesn’t heat after cleaning the filters and checking the settings;
  • The unit was installed recently and heating doesn’t work – Samsung advises that within 3 months of installation the installation should be checked first;
  • You suspect low refrigerant;
  • An error code appears on the display.

Samsung recommends that if the unit is used for both cooling and heating, it should be serviced twice a year – in spring and autumn: cleaning the drainage system and the indoor and outdoor units and checking the system’s operating pressure.

A MasterMan technician will find out on site why your AC isn’t heating, refill freon if needed and repair it – see our AC repair page. If the problem is related to the installation or you want to move the unit, see AC installation and removal. Heating with a gas boiler as well, and it won’t start either? Read Boiler not turning on – what to check.

Frequently asked questions

According to Samsung, for the first 3 to 5 minutes of heating the fan may not run because the unit warms up first so it doesn’t blow cold air.

This is the automatic defrost function, which Samsung says lasts 5 to 12 minutes, after which heating resumes on its own.

Samsung recommends once every two weeks or more often, because dirty filters reduce heating efficiency.

An air conditioner takes heat from the outside air, so at very low outdoor temperatures its heating ability may decrease.

When the AC still doesn’t heat after cleaning the filters, restarting and checking the settings, when an error code appears, or when you suspect low refrigerant.

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