Many Cape Town households rely on their aircon for heating through the wet, cold winter months. When it blows cold air, stops and starts or does not warm the room, it is easy to assume it is broken. Sometimes it is; often it is not. Here is how to tell.
First check the remote is in heating mode (sun symbol) with the temperature above room temperature, and clean the filters. Short pauses with steam from the outdoor unit are normal defrost cycles. If the unit blows cold air continuously, ices up without defrosting, or cools but never heats, the cause is often a reversing valve, sensor, defrost or gas fault that needs a technician.
How an aircon heats
A reverse-cycle aircon heats by running the cooling process backwards. It pulls heat from the outside air, even when it is cold, and releases it into your room. A small valve inside the outdoor unit, called the reversing valve, switches the direction of the refrigerant flow between cooling and heating.
Check these first
The mode
The remote should show heating mode, usually a sun symbol. In auto mode, the unit decides for itself, and in dry or fan mode it will not heat.
The temperature
Set the temperature a few degrees above the room temperature, around 21 to 23 degrees. If it is set lower than the room, the unit has nothing to do.
The filters
Dirty filters restrict airflow, so the unit heats poorly and may overheat and cut out. Clean them every few weeks in winter.
Give it a few minutes
When you first switch on in heating mode, many units wait a few minutes before blowing air, so they do not blast cold air into the room. This is normal.
Normal behaviour that looks like a fault
Defrost cycles
On cold, damp Cape Town mornings, frost can form on the outdoor unit's coil while it is heating. Every so often, the unit pauses heating and briefly reverses to melt the frost. You may see steam rising from the outdoor unit and the indoor fan may stop for a few minutes. This is completely normal.
Water from the outdoor unit
In heating mode, the outdoor unit produces water as it defrosts. Water dripping from the outdoor unit in winter is normal.
Slower heating on very cold days
Heating capacity drops as the outside temperature falls. On the coldest mornings, the room takes longer to warm up.
Real faults
Blows cold air all the time
If the unit blows cold air continuously in heating mode, the reversing valve may be stuck in cooling position, or its coil or control may have failed.
Cools fine but will not heat
A reversing valve fault, a faulty outdoor temperature sensor or a control board issue.
Ices up and does not defrost
Thick ice that builds up on the outdoor unit and never clears points to a defrost sensor or control fault, or low refrigerant.
Weak heating even on mild days
Low gas from a leak, a dirty outdoor coil or a failing compressor.
Error codes
Note the code or flashing light pattern and send it to your technician with a photo of the model sticker.
Preventing winter problems
- Book a service before winter, especially if the unit has not been serviced since summer.
- Clean filters every few weeks when heating daily.
- Keep the outdoor unit clear of leaves, plants and stored items.
- Make sure defrost water can drain away and does not freeze or pool around the unit.
- Use a sensible temperature; very high settings make the unit work harder without warming the room much faster.
Getting the most from winter heating
- Close doors and curtains so the heat stays in the room.
- Use the timer to warm a bedroom before bedtime rather than running it all evening.
- Point the louvres downwards in heating mode, because warm air rises.
- Keep the outdoor unit clear of leaves, pot plants and stored items so it can draw in air.
- If the room never gets warm, the unit may be undersized for heating; a technician can check its output.
Coastal homes
Along the Atlantic Seaboard, Blouberg and False Bay, salt corrosion can cause slow gas leaks that show up first as weak heating in winter. A service every six months on the coast catches corrosion early.
Frequently asked questions
Why is steam coming from my aircon outside in winter?
The unit is defrosting its outdoor coil. Steam and a short pause in heating are normal on cold, damp mornings.
Is it cheaper to heat with an aircon than a heater?
A reverse-cycle inverter aircon is usually much cheaper to run than bar, fan or oil heaters for the same warmth.
My aircon only cools. Can it be fixed to heat?
If it is a reverse-cycle model, yes, the fault can usually be repaired. If it is a cooling-only model, it cannot heat.
A1 Refrigeration is an independent company and is not affiliated with or authorised by any appliance manufacturer. This guide is general advice. For anything involving electricity or refrigerant gas, use a qualified technician.
Need a hand? See our aircon repair and servicing service in Cape Town.