Six common reverse cycle heating problems – and how to fix them

“Regular maintenance is necessary to keep your reverse-cycle air conditioning unit running smoothly. This includes cleaning filters, checking refrigerant levels, and ensuring all components are functioning correctly,” says Cyber Air Conditioning, a local expert in HVAC systems.

Reverse cycle air conditioners are a bit of a household hero, keeping things cool through the heat and cosy during winter. But even the most reliable units have their off days.

Whether it’s blowing cold air when you’re trying to warm up, or making odd noises when it should be humming quietly in the background, these systems can act up from time to time.

If your unit is misbehaving, don’t jump to worst-case scenarios just yet. Many problems have fairly straightforward fixes. Let’s unpack some of the most common issues people run into with reverse cycle systems – and how to sort them out without the headache.

You’ve punched in the temperature. The machine hums to life. But 10 minutes later, it still feels like you’re sitting in a meat locker. Sound familiar?

This one’s often a filter issue. Dirty filters restrict airflow. The air that does make it through? Weak and barely heated. Another possibility is the outdoor unit – if it’s covered in leaves, dirt, or spiderwebs, that could mess with heat exchange.

What to do:

Pop the front panel open and take out the filter. If it’s grey and dusty, it’s time for a rinse (or replacement if it’s beyond saving). Step outside, too. Check that the outdoor unit’s clear and unobstructed. Still no joy? The refrigerant might be low. That’s a job for a technician.

You switch to heat. The unit kicks on. And then – cold air. It's one of those moments that makes you question everything.

But hang on. In cold weather, the outdoor part of your system can freeze up. When that happens, it briefly switches into a defrost cycle, reversing the operation to melt the ice. That means the indoor unit pushes out cool air for a few minutes.

What to do:

If it’s just for a short while, that’s normal. Give it 5–10 minutes. If it keeps happening or the system never goes back to warm – you may be dealing with a reversing valve fault or thermostat issue. Double-check settings first. If all looks good, book a repair.

This one’s called short cycling. Instead of running for 10 or 15 minutes, your unit switches on, runs briefly, then shuts off – only to start up again moments later. Rinse and repeat.

It’s bad for energy use, bad for components, and usually signals one of three things:

• The unit’s too powerful for the space

• The thermostat is picking up misleading temps (sunlight, nearby appliance heat, etc.)

• Or again… dirty filters.

What to do:

Start with the easy stuff: clean the filter, move the thermostat if it’s near a window, and make sure no warm appliances are skewing its readings. Still happening? You might have an oversized system – very common in quick installs. You’ll need an HVAC pro to assess and recalibrate.

Burnt toast. Damp socks. Dust. If your heating kicks on and brings an aroma with it, trust your nose. Something’s not right.

Musty smells tend to mean mould or bacteria has set up shop inside the unit – often due to moisture buildup and a lack of recent cleaning. Electrical or smoky smells, however, need immediate attention. Don’t wait those out.

What to do:

Turn the system off. Clean or replace the filter. If the smell persists, you may need a technician to deep-clean the internal coil or inspect for any wiring issues. Inhaling mouldy air isn’t just unpleasant, it’s unhealthy.

This one’s more common in colder parts of the country. If you head outside and find the condenser coated in frost or ice, the system might not be defrosting as it should.

When the ice builds up too much, it can’t pull in outside air properly. That means poor heating – or no heating at all. And if left long enough, it can even damage components.

What to do:

Turn the system off and let the ice melt naturally. Don’t pour hot water or chip at it. Clear away leaves and debris while you’re at it. If it keeps freezing over, you might be dealing with a faulty defrost sensor or low refrigerant. Time to bring in a qualified technician.

Sometimes, the issue has nothing to do with the unit itself. The problem? That tiny plastic remote you’ve probably dropped 10 times.

Dead batteries, poor signal range, or an outdated sensor can all stop your commands from reaching the indoor unit. In systems with wall-mounted thermostats, the same rules apply – power supply issues, damaged wiring, or interference from nearby electronics can all throw things out of whack.

What to do:

Swap the batteries first. Then, try a reset using the manual (most remotes have a tiny pinhole for this). Keep the remote aimed directly at the unit and remove anything blocking its path. Still no luck? The sensor or controller board inside the unit might be the issue.

Many of the issues above can be nipped in the bud with basic maintenance: clean filters, clear outdoor units, and yearly servicing. If your system’s over five years old and hasn’t had a professional look in a while, it’s well overdue.

And the payoff? Reverse cycle units are among the most efficient heating options available today. In fact, according to Energy.gov.au, the models on the Australian market typically deliver between 300% and 600% energy efficiency.

That means for every unit of electricity used, you could be getting three to six units of heating or cooling in return – but only if the system is running as it should.

A good reverse cycle system should last well over a decade. But it’s not a fire-and-forget appliance. It needs attention – just like your car or computer.

So next time something feels off, don’t ignore it. Listen to the sounds. Smell the air. Check the temperature after 10 minutes. With a bit of regular care and a willingness to troubleshoot early, your system can stay reliable, efficient, and blissfully warm – exactly when you need it most.