Daikin VRV IV RXTQ-TA / RXTQ-TB error code MC
Address duplication and poor setting, warning
Which models this applies to. System
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, MC is a fault. It means address duplication and poor setting, warning. A first thing to check: A duplicated controller address.
- Applies to
- Daikin VRV IV RXTQ-TA / RXTQ-TB
- Daikin VRV IV RXTQ heat pump codes · Heat Pump
- Type of code
- Fault
- Urgency: Worth keeping an eye on
- First safe check
- List every controller address on the system and look for the duplicate, which is the whole of the diagnosis.
What MC means on this model
A centralized controller has a duplicated address or a setting the system will not accept. The system keeps heating and cooling, but the duplicated controller cannot be individually addressed or controlled.
Symptoms you will notice
- System shows MC
- One controller cannot be individually identified or controlled
- Two controllers show the same units
- The fault followed adding or replacing a controller
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 duplicated controller address
- A controller restored to a default address that collides with an existing one
- A poor or incomplete field setting on a controller
- A controller added without being addressed
- An addressing error during commissioning
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.
- List every controller address on the system and look for the duplicate, which is the whole of the diagnosis.
- Check whether a controller was recently replaced or added, since a replacement defaults are a frequent source of a collision.
Do not do these
- ×Do not leave the duplication in place, because the system keeps running while one controller is effectively unreachable.
- ×Do not change addresses on controllers you have not listed, because the duplicate is only identifiable by comparing all of them.
When to call a technician
No call needed yet, but write it down
Note the date and the exact code, and watch whether it comes back. If it turns into a repeat fault or starts affecting performance, that is when it becomes worth a technician.
- 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.
What it costs to fix
Parts
None expected.
Labor
One to two hours to correct the address or field setting.
DIY or technician
A commissioning 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.