mypros+
Error code reference

Daikin Air Conditioner Error Code AJ

Capacity setting abnormality

Daikin codesDaikin air conditioner codes
Avg. service call
$285
National average. Trip fee plus diagnostic plus labor. Before parts.
MyPros+ 3-day pass
$9.95
Same diagnostic steps, on your phone. Start now.
You keep in your pocket
~$275
Even before you buy the part.
Skip the service call. Fix it yourself.
Full procedure unlocks instantly.
Get Started

What the AJ error code actually means

Your Daikin air conditioner's control board does not know what size unit it is supposed to be managing, either because it was recently replaced or because a small configuration plug called a capacity setting adaptor is missing. This is not a refrigerant or compressor problem, it is a setup or configuration issue with the indoor unit's electronics. A technician can resolve this by connecting the correct adaptor or reprogramming the board.

Diagnostic procedure

The full AJ procedure

Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.

MyPros+ · DiagnosticsStep 1 preview
1
First diagnostic step
Check if indoor unit PCB was replaced with spare PCB; install capacity setting adaptor if needed.
Unlock with pass
Unlock with pass
Unlock with pass
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
Unlock AJ procedure $9.95

Or subscribe: $29/month for unlimited access to all codes plus Max AI diagnostics.

Most common causes of AJ

Ranked by how often they cause this code
  1. 1Spare PCB installed without capacity setting adaptor
  2. 2Capacity setting adaptor not connected
  3. 3PCB memory fault on original board
  4. 4Incorrect spare PCB installed

Most DIYers save hundreds by diagnosing before ordering parts.

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass

Questions people ask about AJ

What does AJ mean on a Daikin air_conditioner?
The AJ code means the indoor unit's PCB cannot find the capacity code it needs to identify the unit's size and configuration. This happens either because the PCB was replaced with a spare board that has no pre-loaded capacity code, or because the capacity setting adaptor is not connected to the board. It is a configuration error, not a mechanical or refrigerant fault.
Is it safe to run my Daikin air conditioner with the AJ error code showing?
A unit displaying AJ will generally not operate normally because the PCB lacks the configuration data it needs to manage the system correctly. Attempting to run the unit in this state is not recommended, as the board cannot apply the correct operating parameters for the indoor unit's capacity. The error should be resolved before resuming normal operation.
How much does it cost to fix a Daikin AJ error code?
Repair costs depend on what components are needed. If only a capacity setting adaptor is required, the part cost is relatively low, but labor charges for a qualified HVAC technician will apply, typically putting the total in the range of $80 to $250. If the PCB itself has failed and requires replacement, costs can rise to the $300 to $700 range or higher depending on the unit model and local labor rates.
Can I fix the AJ error code myself on a Daikin unit?
Resolving AJ requires identifying whether the PCB was recently replaced and whether a capacity setting adaptor is present and correctly connected. Sourcing the correct adaptor and installing it on the PCB is a task most comfortable for experienced technicians familiar with Daikin indoor unit electronics. DIY repair is possible for knowledgeable individuals but requires the correct adaptor part for the specific model.
Will resetting my Daikin air conditioner clear the AJ error code?
Resetting the unit will not clear the AJ code permanently. Because the error is caused by missing configuration data on the PCB rather than a temporary sensor or communication glitch, the fault will return immediately after power is restored until the underlying issue is corrected. The capacity setting adaptor must be installed or the correct PCB must be configured.

Related Daikin air conditioner error codes

All Daikin air conditioner codes

78,000+ service manuals · 160,000+ error codes · 55+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass