Daikin VRV IV RXTQ-TA / RXTQ-TB error code C9
Suction air thermistor abnormality
Which models this applies to. Indoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, C9 is a fault. It means suction air thermistor abnormality. A first thing to check: A failed suction air thermistor.
- 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
- Check the connector and the wire at the suction air thermistor.
What C9 means on this model
The sensor that reads air returning to the indoor coil is not reporting a usable value, and the unit has stopped. A blocked return grille is a common contributor, because a sensor sitting in still air reads falsely.
Symptoms you will notice
- Indoor unit shows C9 and stops
- The unit will not heat or cool
- A remote or wall sensor has been recently added or moved
- The return air path around the sensor is obstructed
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:
- A failed suction air thermistor
- A wiring or connector fault at the sensor
- A failed remote or wall controller sensor
- An obstructed return air path that has left the sensor reading stagnant air
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.
- Check the connector and the wire at the suction air thermistor.
- Confirm the return air grille is not blocked, because a sensor sitting in still air will read high and the control will treat it as a fault.
- For a remote sensor, check the controller connection and whether the sensor has been installed in a spot with no airflow.
Do not do these
- ×Do not block a return grille to improve airflow elsewhere in the room. The suction sensor is reading the return air, and starving it produces this code.
- ×Do not swap suction and remote sensors on the assumption they are interchangeable.
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.
Checking a return grille is a homeowner task. Replacing the sensor is a technician job.
What it costs to fix
Parts
Suction air thermistor $30 to $90. Remote or wall sensor $60 to $200.
Labor
One to two hours to test and replace.
DIY or technician
Checking a return grille is a homeowner task. Replacing the sensor is a technician job.
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.