Air Conditioning Not Turning On
There's a useful distinction between air conditioning that's underperforming and air conditioning that simply won't respond at all, no lights, no beep, nothing. A totally dead unit points towards power supply, isolator, or control board issues rather than refrigerant or compressor faults, which narrows things down before an engineer even arrives.
Working through the checks below in order will often either solve the problem outright or give us useful information to bring the right parts on the first visit.
Start with power, not the unit
- Check the fused spur or isolator switch near the outdoor unit hasn't been switched off or tripped
- Check the relevant breaker at the consumer unit
- Confirm the remote control has working batteries and try standing closer to the unit's receiver window
- Look for a small standby light on the indoor unit even if the display itself is blank, which suggests partial power
If power is confirmed present
A unit with confirmed power but still no response usually has a fault at the control board, a failed transformer inside the indoor unit, or a wiring fault between indoor and outdoor units. These aren't things to investigate by opening the casing yourself, both for safety and because the boards are easily damaged by static or incorrect handling.
Why professional diagnosis matters here
Because a dead unit could be anything from a blown fuse the size of a match to a control board that needs replacing, proper diagnosis with a multimeter at each stage of the circuit is the only reliable way to isolate the fault rather than replacing parts speculatively.
What we check on arrival
We test the supply at the isolator and fused spur, then trace power through to the indoor unit's control board and transformer, checking each stage. If the fault is a specific component such as a transformer or board, we'll confirm the part and cost before ordering anything, since lead times vary by brand and model.
Avoiding this in future
Isolators and fused spurs can develop internal faults over years of use in outdoor conditions, and it's a cheap check to include at each annual service alongside the refrigeration side, rather than waiting until the unit goes completely dead.
FAQs
Common questions
Could a power cut have caused this?
Yes, some units need manually resetting at the isolator after a power interruption, or occasionally develop a fault from a surge during the outage.
Is it worth replacing the remote batteries before calling anyone?
Definitely, it takes thirty seconds and is a genuinely common cause of a unit appearing completely dead.
How do I know if the fault is the isolator or the unit itself?
If you have a multimeter and know how to use one safely you can check voltage at the isolator, but this is best left to an engineer if you're not confident with electrical testing.
Will a dead control board mean a whole new unit?
Not usually. Control boards and transformers are typically available as individual parts, though lead time depends on the brand and model age.
Keep reading
More from our knowledge base
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