Daikin VRV IV RXTQ-TA / RXTQ-TB error code A8
Indoor unit power supply voltage abnormality
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, A8 is a fault. It means indoor unit power supply voltage abnormality. A first thing to check: Supply voltage outside the acceptable range at the fan motor.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Needs attention soon
- First safe check
- Measure the supply voltage at the fan motor, which is where the manual directs the check for A8-01, and compare it with the nameplate voltage for the unit.
What A8 means on this model
The indoor unit has seen a supply voltage outside what it can run on and has shut the fan down to protect itself. Sub-code A8-01 narrows it, and the manual directs checking the input voltage at the fan motor.
Symptoms you will notice
- Indoor unit shows A8 and stops
- The indoor fan does not run even though the outdoor unit is running
- The unit trips when a large load starts elsewhere on the same supply
- Lights dim when the fan starts
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:
- Supply voltage outside the acceptable range at the fan motor
- A loose or corroded supply connection at the indoor unit
- Undersized or overloaded wiring feeding the indoor unit
- A starting capacitor or supply component in the indoor unit
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.
- Measure the supply voltage at the fan motor, which is where the manual directs the check for A8-01, and compare it with the nameplate voltage for the unit.
- Note whether the fault happens only when another large appliance starts, which points at the supply rather than the unit.
- Check that the supply connection at the indoor unit is tight and free of corrosion.
Do not do these
- ×Do not replace the indoor fan motor on an A8 code. The manual frames A8 as a voltage fault, and the motor is what is reporting it.
- ×Do not measure inside the indoor unit with the power on unless you are qualified to do so.
When to call a technician
Book a technician, do not keep resetting it
This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.
- 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 technician job. Voltage measurement at the unit is not a homeowner task.
What it costs to fix
Parts
Supply terminal block or capacitor $40 to $150. Fan motor $150 to $400 if the motor has been damaged by the fault.
Labor
One to two hours to measure and correct the supply.
DIY or technician
A technician job. Voltage measurement at the unit is not a homeowner task.
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.