Why Did All My Aircon Units Stop Working at the Same Time?
Several indoor units failing at the same moment points to the one thing they share. They all depend on a single outdoor unit. What that outdoor unit is doing narrows it quickly.
By Team Snowflake | Updated 20 Sept 2026
Why did all my aircon units stop working at the same time?
- A failed communication circuit on the outdoor board can stop several indoor units together.
- Power not reaching the outdoor unit leaves the indoor units running warm.
- An outdoor unit at the end of its life takes the whole system down with it.
1. Outdoor control board no longer communicating
Every indoor unit showing the same error at the same time usually means the outdoor board has stopped producing the signal that keeps them in step. The indoor units are working and sending correctly. Without a reply from the outdoor board, they all stop together.
How to tell
Matching errors across several indoor units suggest a shared problem rather than separate room faults. Unlike a gradual decline, the stoppage can be simultaneous. The code must be interpreted for the model; it does not by itself prove that only the outdoor board has failed.
- Every indoor unit shows the same error code.
- The indoor units power up and respond to the remote.
- The outdoor unit is silent and never kicks in.
- It happened to all of them at the same moment.
How we confirm it
We confirm the signal reaching the outdoor terminal and test whether the board is replying. The board is then quoted only once the wiring has been cleared as sound.
Do not let anyone replace indoor units for this. They are all reporting the same upstream fault, so swapping them changes nothing while the outdoor board stays silent.
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2. Power not reaching the outdoor unit
Indoor units that run normally and blow air that never turns cold, with no error at all, point to the outdoor unit having no supply. An isolator switched off, a tripped breaker, or a failed supply leaves the indoor fans running on their own circuit while nothing outside starts.
How to tell
Supply checks distinguish this path, rather than the absence of an error code alone. Indoor fans may keep running while the outdoor unit stays silent, but that does not confirm a lost supply. A technician verifies where power stops before ruling out other faults.
- No error code anywhere, the units just blow warm air.
- The indoor fans run normally and respond to the remote.
- The outdoor unit is completely silent, not even a hum.
- Someone has recently worked near the isolator or the board.
How we confirm it
We check the isolator, the breaker and the supply at the outdoor terminal to find where power stops. The cause of any trip is then established before the circuit is restored.
Do not simply switch a tripped breaker back on and leave it. It cut the supply for a reason, and resetting it without finding that reason feeds the same fault again.
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3. The outdoor unit has reached the end of its life
An older outdoor unit in an exposed position can simply run out. Salt-laden or industrial air eats into the coil over years, and the compressor goes with it. The indoor units are often in far better condition, because they never faced that air.
How to tell
Instead of an electrical fault, this path is wear: cooling had been fading for a long time before the stoppage. The outdoor unit shows visible corrosion instead of working but silent hardware.
- The outdoor unit is old and sits somewhere exposed.
- Corrosion, furring, or eaten-away fins are visible on the coil without opening the unit.
- Cooling had been fading for a long time before it stopped.
- The indoor units are visibly in much better condition.
How we confirm it
We assess the outdoor unit against the indoor units separately, so the decision covers only what has actually failed. Replacing the outdoor unit alone is often the honest answer.
A full system replacement is not the fix when only the outdoor unit has gone. The indoor units may have years left, so pricing the whole system misses the cheaper and correct option.
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Describe your situation
Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.