Daikin VRV IV RXTQ-TA / RXTQ-TB error code LC
Transmission error between the outdoor board microcomputers
Which models this applies to. Outdoor unit
Quick answer
On Daikin VRV IV RXTQ-TA / RXTQ-TB, LC is a fault. It means transmission error between the outdoor board microcomputers. A first thing to check: A failed outdoor unit main PCB.
- 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
- Note whether the fault clears completely on a power cycle, because an intermittent internal communication fault often points at the board power supply or moisture rather than a solid failure.
What LC means on this model
The microprocessors on the outdoor main board are not communicating with each other, so the outdoor unit has stopped. This is an internal board fault, not a wiring fault between units, which is what separates it from a U4 style communication code.
Symptoms you will notice
- Outdoor unit shows LC and the system stops
- The system will not respond to the indoor unit
- The fault is intermittent and may clear on a power cycle
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 outdoor unit main PCB
- A failed power supply section on the main board
- A failing microcomputer on the main board
- Intermittent power or a supply problem at the outdoor unit
- Moisture or contamination on the board
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.
- Note whether the fault clears completely on a power cycle, because an intermittent internal communication fault often points at the board power supply or moisture rather than a solid failure.
- Check the outdoor unit supply and connections before concluding the board has failed.
Do not do these
- ×Do not confuse this with an indoor to outdoor communication code. This one is entirely within the outdoor board and the wiring to the indoor units is not involved.
- ×Do not open or clean the board with the power switch on.
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.
What it costs to fix
Parts
Outdoor unit main PCB $600 to $1,400.
Labor
Two to four hours to diagnose and replace.
DIY or technician
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.