Daikin VRV IV RXTQ-TA / RXTQ-TB error code AJ
Capacity setting error
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, AJ is a fault. It means capacity setting error. A first thing to check: An incorrect capacity setting stored in the indoor unit PCB.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Book a technician
- First safe check
- Confirm the capacity setting in the field settings against the model of indoor unit actually installed, because the setting is a stored value rather than a measurement.
What AJ means on this model
A commissioning code rather than a failed part. AJ-01 is a capacity setting error on the indoor board and AJ-02 is an electronic expansion valve setting error, covering the gear type and direct acting type valve settings. Changing the setting is not the same as replacing a board.
Symptoms you will notice
- Indoor unit shows AJ
- The unit runs but does not deliver its rated capacity
- The system was recently commissioned or reconfigured
- A capacity adaptor or field setting was changed
Common causes
The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:
- An incorrect capacity setting stored in the indoor unit PCB
- A fault in the setting of a gear type or direct acting type electronic expansion valve
- A capacity setting that does not match the indoor unit actually installed
What you can safely check
These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.
- Confirm the capacity setting in the field settings against the model of indoor unit actually installed, because the setting is a stored value rather than a measurement.
- Note whether the unit has just been commissioned or had field settings changed, which is when this code appears.
Do not do these
- ×Do not change capacity settings in the field without the design data for the system, because the setting drives the expansion valve metering across the whole system.
- ×Do not treat AJ as a failed indoor unit PCB. The manual describes it as a setting error, and a board replacement does not fix a wrong setting.
When to call a technician
Worth scheduling, and worth your own checks first
You can usually keep living with this for a short while, but it will not fix itself. Do the safe checks below first, because a tripped switch or a blocked airflow is a five-minute fix that would otherwise cost you a service call.
- The refrigerant circuit is sealed and legally requires licensed handling. Opening it without certification releases refrigerant and can put the whole system in violation of regulation, so a low-pressure or high-pressure fault on this equipment is a call-out, not a weekend job.
- If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.
A commissioning technician job. The field settings are password protected on this class of equipment.
What it costs to fix
Parts
None expected. This is a configuration code.
Labor
One to two hours to read and correct the field setting.
DIY or technician
A commissioning technician job. The field settings are password protected on this class of equipment.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- Daikin VRV IV RXTQ heat pump codes
- Models in scope
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.