Reverse Cycle Air Con Not Heating? 11 Causes & Solutions

Reverse Cycle Air Con

Reverse cycle air conditioners can be a lifesaver, providing you with the heating you need without spending money on a separate unit for heating and cooling. When something goes wrong, however, you can find yourself without effective climate control in the colder months. 

When one split system or ducted unit is in charge of your home’s heating and cooling, it’s important to be able to identify issues as they arise and get them fixed as soon as possible.

If your reverse cycle AC isn’t heating properly, you may be dealing with incorrect settings, dust or ice build-up, damaged parts, leaks, or incorrect sizing. Some of these issues can be resolved yourself, but others require a professional, and the first step is to troubleshoot the problem. 

Not sure where to start if your air conditioner just won’t blow hot air? Don’t worry, we’re here to help. With years of hands-on experience with air conditioner servicing in Perth, we’ve put together this helpful guide to troubleshooting reverse cycle heating problems. 

Read on for more information about reverse cycle AC issues and how to fix them.

How Does Reverse Cycle Heating Work?

Reverse cycle air conditioners use a ‘heat pump’ method to change air temperature through a process of heat exchange. In heat mode, the outdoor unit extracts heat from the air outside and delivers it into your home. Even in cold temperatures, the reverse cycle unit can still absorb heat efficiently.

The outdoor unit draws in air from the outside and passes it over a set of coils. These coils contain a refrigerant that absorbs heat from the air as it passes over them. Winter weather is no obstacle – a reverse cycle AC unit can still extract heat in temperatures as low as -15℃.

Once the heat is absorbed, the refrigerant then flows to the indoor unit where it releases the heat, warming the air inside your home. The cooled air is then passed back outside, completing the cycle. 

If you have a split system reverse cycle AC, the warm air will come from your wall unit. For ducted reverse cycle air con, your heating unit will distribute air through your ductwork and vents. 

This process is reversed in cooling mode, with the air conditioner drawing heat from the inside of your home and releasing it outdoors. As a result, a reverse cycle air conditioner can provide both heating and cooling all year round, making it an ideal choice for homeowners in Australia.

11 Common Reasons for Reverse Cycle Air Conditioners Not Heating

You may encounter some of the below issues if your reverse cycle system isn’t maintained regularly. Here are 11 common reasons why your AC isn’t heating.

1. Ice Build-Up on the Outdoor Unit

Ice build-up on your outdoor AC unit can prevent your unit from heating properly. The build-up can happen due to poor ventilation, poor maintenance, or age. 

The outdoor unit needs to keep itself warm to support heat exchange efficiency. However, since it is outdoors, it is exposed to freezing weather in winter. Ice build-ups are more common if your unit is in a tight space with restricted airflow.

To fix ice build-up in your outdoor unit, you can turn it off and let the ice defrost. Some air conditioning units also have an automatic defrost mode. When installing your unit, ensure that the unit has plenty of space, especially where the fan is located. Maintenance and age also play a part in ice build-up.

2. Blocked or Dirty Air Filters

The filters in your air conditioner keep the air in your home clean. These filters capture dust, dirt, and other small particles your air conditioner accumulates and picks up. As a result, they will eventually become dirty or clogged.

As the filters become more clogged, the compressor or other parts of your unit can stop working, resulting in no hot air.

To deal with blocked or dirty air filters, clean them regularly and replace them as needed. Depending on how comfortable you feel handling the machine, you can either clean your air filters yourself or hire a professional air con cleaner.

3. Incorrect Settings

If your system isn’t on the right setting, it won’t heat your home. This sounds silly, but it is pretty common. It may be due to forgetfulness or accidentally setting it to the wrong mode (such as Cool or Auto in the summer).

Make sure that you check your thermostat or remote control to see if the heat setting is on. You can also check and adjust the temperature as necessary. Some units don’t automatically heat unless your indoor temperature is extremely low.

4. Dirty Coils

Like dirty air filters, dirty coils can prevent your heating from working correctly. The air won’t flow efficiently if the coils are dirty or have gathered too much debris.

Although you can clean the coils yourself, the coils are pretty delicate and might require professional help. Getting your evaporator and condenser coils cleaned professionally at least once a year is recommended.

5. Low Refrigerant Levels

When your refrigerant levels are low, your unit will not only fail to heat properly, but your utility bills will also skyrocket. Typically, AC units don’t run out of refrigerant gas. However, refrigerant levels can become low if there is a leak. 

Air conditioner leaks are usually caused by impact, damage and wear over time on units that aren’t regularly maintained. Besides failing to heat, other signs that your unit is low on refrigerant are increased humidity, a longer cooling time, and hissing noises.

If your air conditioner has recently had a leak fixed by an unskilled technician, and your system isn’t heating properly, it may be low on refrigerant. 

6. Damaged Fans

Clogged filters or coils can damage your fans and prevent your unit from heating properly. The AC unit might still be producing hot air, but if the fans are broken, the air won’t circulate.

This issue can be identified by checking the fan to see if debris is preventing it from spinning. If that’s the problem, a simple cleaning will fix it. Otherwise, contact a professional HVAC technician.

7. Being Stuck in Defrost Mode

The defrost mode is automatically activated if it’s extremely cold outside and there is ice build-up in the unit. If you suspect the defrost mode has been on for too long, though, your unit might need a fix.

Sometimes, your system can get stuck in defrost mode because of other issues, such as broken fans or a problem with your settings.

It is best to call a professional to resolve this, especially if you smell burning plastic or rubber.

8. Circuit Breaker or Blown Fuses

Reverse cycle heating needs electricity to run. Electrical issues, such as a tripped circuit breaker or blown fuse, can also prevent your AC from heating properly. Older homes may encounter this more often as other appliances share a circuit with the AC.

If your circuit breaker has tripped, you can try resetting it and turning off other appliances on the same circuit. Repeated trips may indicate a fault with your air conditioner, though, so be sure to call in a qualified technician. It’s always best to leave electrical issues to trained and licensed electricians. 

9. Debris Obstructing the Outdoor Unit

Since your outdoor unit is exposed to the elements every day, it’s possible that your AC isn’t heating due to debris obstructing it. If this is the case, a simple clean-up can do the trick. 

Installing a roof or cover over your outdoor unit is a good idea to prevent branches or leaves getting stuck in it.

10. A Malfunctioning Thermostat

The thermostat is a regulating device for the temperature of your air conditioner. If it malfunctions, your unit won’t heat the room properly because it cannot accurately sense the temperature inside.

If the thermostat is not set to heat or the temperature needs to be higher, that’s a simple adjustment you can make. However, if the issue is a broken thermostat, you need to call a technician to fix it.

11. Your Unit is Missized

Air conditioner capacity should be optimal for the size of your home. If your unit is drastically smaller than the area you want to heat, the machine will struggle to work efficiently, potentially resulting in little to no heating. 

The only way to deal with this is to replace it with an appropriately sized air conditioning unit. If you’re unsure if this is the cause of your problems, speak to an air conditioning specialist. They can perform a size calculation and ensure your reverse cycle AC unit is correctly sized for your home. 

How to Fix Mitsubishi Air Conditioner Heat Mode Not Working

To get your Mitsubishi AC’s heating function working, you must ensure it’s on the correct Heat Mode setting. In some cases, remote adjustments are sufficient to fix the problem, while in others, more attention is required.

For basic troubleshooting of your Mitsubishi Reverse Cycle Air Conditioner, here are some steps to follow:

  1. Check if it’s on Heat Mode or Auto Mode  – For your Mitsubishi AC to heat, it has to be in Heat mode, so make sure the sun symbol is lit.

  2. Set the Recommended Temperature – Once you’re sure that the unit is in Heat mode, you can set your desired temperature. Mitsubishi recommends anywhere from 18°C to 22°C for maximum comfort.

  3. Reset the Air Mitsubishi Conditioner – For Mitsubishi Electric air cons, switch off the indoor unit and then the outdoor unit. Wait for at least 30 seconds before turning on the outdoor unit and then the indoor unit.

    You can also use the Mitsubishi split system remote. Press the power button for a couple of seconds. When several blinking lights appear on your unit, it will automatically restart itself.

    For Mitsubishi industrial AC units, unplug them first from the power point. Then, switch off the outdoor unit’s isolator or shut down the power from the main electrical board. Leave it for 15 to 30 minutes before turning everything back on.

  4. Check for Error Codes – You can see the error codes on a sticker pasted on your unit. The type of blinking (continuous blinking) or the number of blinks (2, 3, 4, 5, 6, 7, and 14) will tell you how to troubleshoot your unit and which part of the system it is (indoor or outdoor).

  5. Call an AC Repair Service – If any of these initial diagnoses and steps don’t work, it’s best to call a licensed HVAC technician to come and fix your unit.

How to Fix Samsung Air Conditioner Heat Mode Not Working

Samsung reverse cycle air conditioners will not heat when settings are incorrect or there are functional issues, which you can identify using the error codes. 

Here’s a guide to help you with troubleshooting your Samsung air con heating:

  1. Ensure Settings are Correct – To get your Samsung AC Heat mode to work, ensure that you’re in Heat mode. You can tell by checking the remote control. Press the mode button multiple times to get to Heat mode. Then, adjust the temperature as necessary.

  2. Reset the Samsung Air Conditioner – Turn off the unit using the remote to reset your AC. Then, turn off its circuit breaker for 30 to 60 seconds before turning it back on. Wait for at least 30 minutes before using your AC.

  3. Check for Error Codes – There is a screen on Samsung AC units. It will tell you the error code, which usually consists of letters, numbers, and sometimes a symbol (*). Some units, however, have colour-coded LED lights on display that correspond to specific errors. Make sure to check your manual to understand and troubleshoot the error message.

  4. Book an AC Service & Repair – You should call a licensed technician to check out your unit if these tips don’t work. 

Can I Fix My Reverse Cycle Air Conditioner Myself?

You can fix some issues yourself, such as setting your reverse cycle AC to the right settings and cleaning the filters. However, more complex repairs are best left to the professionals.

HVAC technicians are required for more complex issues, such as replacing fuses or handling refrigerant leaks. Leave it to the professionals to avoid higher repair costs rather than attempting to fix your system yourself.

Reverse Cycle Heater Troubleshooting FAQs

How Can I Tell If My Air Conditioner is Reverse Cycle?

The easiest way to tell if your air conditioner is a reverse cycle unit is to check your remote or the AC screen (if it has one) and look for the heat mode symbol, which is usually a sun. 

What is Heat Mode on my Air Conditioner?

The heat mode is used during winter to keep your room warm. Reverse-cycle air conditioning units blow warm air into a room during heat mode. The outdoor unit will slow down once it reaches a certain temperature setting, and active heating will resume if the inside temperature becomes cool again.

How Long Does it Take an Aircon to Heat?

The time it takes a room to heat depends on the room size, though for an average room, it takes approximately five minutes. When you turn on your AC in heating mode, the fan doesn’t blow straight away so that cold air isn’t suddenly expelled. This is why it takes a little while to feel the warmth.

What Mode is Heat on an Air Conditioner Remote?

On the screen of an AC remote or controller, you will see the word “heat” or a sun symbol to indicate heat mode.

What Temperature Should I Set my Reverse Cycle Heating to?

There is no hard and fast rule, but experts suggest the ideal winter temperature setting in Australia is 18°C to 20°C. However, the perfect temperature setting will depend on how well your home is insulated and your local climate. 


This article is published in good faith and for general informational purposes only. It does not constitute an estimate or quote for any specific service. Platinum Power & Air does not make any warranties about the ongoing completeness, reliability and accuracy of this information. This article is not intended to replace consultation with a licensed air conditioning technician. 

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