Air conditioner [How to get the fault code]a plain-English guide

A domestic split has nowhere to show you a code, which is why so many people conclude their air conditioner has simply stopped with no explanation. The fault is recorded; you just have to know how to ask for it, and the procedure is different for every manufacturer. Read the one for your brand rather than a generic one. Daikin publish theirs in the owner's manual rather than an installer document, which is unusually helpful, and it works through the remote. Hold Cancel for five seconds and a blinking 00 appears in the temperature display. Then press Cancel repeatedly and listen, because the beeps are the interface: a short beep or two consecutive beeps mean the code being shown does not apply to your unit, and a long continuous beep means it does. That is the code you want. Hold Cancel for five seconds again to exit, or leave it a minute and it cancels itself.

Mitsubishi's wired controllers show the two-character code outright. On a wireless remote the unit answers by counting: the Mr Slim self-check is CHECK twice, the temperature buttons to set the address, then HOUR with the remote pointed at the unit, after which the indoor unit beeps and blinks its lamp a number of times that is the code — five for P5 — with the lamp held on for about three seconds first if the fault is in the outdoor unit. Mitsubishi's domestic MSZ wall units never show a two-character code at all; they report by the same blink count, and the owner instruction for a blinking lamp is to stop and consult the dealer. Toshiba's domestic range carries a warning that is the whole reason this page exists. Their technical handbook, in its own words, says not to turn off the power supply before reading the fault codes, because doing so clears the diagnostic memory. Their current service manual for the latest wall units says the opposite — that a power cycle resets the unit but the codes stay in memory until cleared — and since you cannot tell from the room which behaviour your unit has, the safe rule is the handbook's. Everyone's first move on a misbehaving appliance is to switch it off and on again, and on this equipment that may erase the evidence.

The handbook's procedure is to press CHK to enter service mode, step through with the timer buttons until all the lights flash with the buzzer, read the code, and press CLR to clear it — at which point the controller shows 7F; on the current units the CHECK button is on the back of the remote under the battery cover, the temperature buttons step through the codes, one beep means the code shown does not apply and ten seconds of beeping with every lamp flashing means it does, which is not a fault but confirmation of the clear. Toshiba also read as a pair: an initial code of 01, 02 or 03 plus a detail code. Fujitsu are the awkward case, because the same fault is published in four different forms — the code on the remote, a pattern of operation-lamp and timer-lamp flashes, a wireless indicator, and a message in their app. Two owners with an identical fault can be searching entirely different strings. If you are counting flashes on a Fujitsu, you are reading a different representation of the same thing.

1. 1

   Identify the manufacturer before you touch anything, because the retrieval procedures are genuinely different and some are destructive if done in the wrong order.

2. 2

   Do not switch the power off first if you have a Toshiba. Their technical handbook’s instruction is that powering down clears the diagnostic memory before you have read it, and although the current service manual says the newest units keep the code, reading first costs nothing either way.

3. 3

   On a Daikin, hold Cancel on the remote for five seconds until 00 blinks, then press Cancel repeatedly and listen for a long continuous beep — that marks the code that applies to your unit.

4. 4

   On a Toshiba, enter service mode on the remote — CHK on the older controllers, the CHECK button under the battery cover on the current ones — and step through with the timer or temperature buttons until all the lights flash with the buzzer. Note both the initial code and the detail code. On a Mitsubishi with a wireless remote, press CHECK twice, then HOUR with the remote aimed at the unit, and count the beeps and blinks.

5. 5

   Write it down exactly as shown, including any leading zero and whether a character is a letter or a digit. Fujitsu’s codes mix digits with the letters A, C, F, J, P and U — 5A is a real one — so a letter beside a digit is easy to misread.

6. 6

   Give the code to whoever attends. It is the single most useful thing you can hand an engineer, and it decides what they bring with them.