Multi-Split Air Conditioner Not Working? Here's What to Try First
Multi-split air conditioning systems are a great way to heat or cool different rooms using one outdoor unit — but when the seasons change, they can act up in ways that confuse a lot of homeowners.
At Artarmon Air Conditioning, we often get calls from people saying, “My aircon isn’t working” — and in many cases, it’s a multi-split issue that can be fixed without a service call.
Here’s why this happens, what to try first, and how to know when it’s time to call in the pros.
Why Multi-Split Systems Can Be Confusing
Unlike regular split systems, multi-split air conditioners share a single outdoor unit between multiple indoor units. That means:
The system can only operate in one mode at a time: either heating or cooling — not both.
If one room is set to heat and another to cool, the system may become unresponsive or not work at all.
You may see error codes or find that indoor units blow air that doesn’t match the selected mode.
This issue is most common during seasonal changeovers, when people start switching between cooling and heating.
Quick Reset: The Fan-Only Trick
If your multi-split isn’t responding properly, try this first:
Turn all indoor units to FAN ONLY mode.
(This stops the system from trying to heat and cool at the same time.)Wait a few minutes for the outdoor unit to fully shut down.
Set all indoor units to the desired mode — either heating or cooling — and select your preferred temperature.
Turn the units back on one by one. Wait a few seconds between each unit to let the system register the change.
This helps reset the communication between the indoor and outdoor units and can resolve a lot of issues without needing a technician.
Other Common Issues and Tips
Mismatch in remote settings: Double-check that all units are set to the same mode (all heat or all cool). Even one unit set incorrectly can stop the system from operating.
Filters need cleaning: Dirty filters can cause airflow issues, especially if only one indoor unit is struggling. Clean your filters regularly.
Outdoor unit might be in defrost mode: If you're using heating and the outdoor unit appears to stop, it may just be cycling through defrost mode. This is normal during cold weather.
Power cycle the system: Turn off the power to the system at the isolator switch or circuit breaker for 2–3 minutes, then turn it back on. This can clear minor faults or communication issues.
When to Call Artarmon Air Conditioning
If you’ve tried the reset steps and:
Your units still aren’t blowing hot or cold air
The outdoor unit doesn’t start at all
You see flashing lights or error codes
One or more indoor units won’t respond at all
…it’s time to call in a professional.
We’ll diagnose the system, check communication between units, inspect for faults, and make sure everything is working as it should.
Artarmon Air Conditioning is here to help. Whether it's a communication issue, sensor fault, or something more complex, we'll get it sorted quickly and properly.
Need help with your multi-split system?
Book a service visit online and let the experts take care of it.
