Carrier AC error codes – VRF Full DC Inverter - outdoor unit
35 codes from the Carrier service manual, with what each one means and the usual causes. Codes with x prefix: x = system (1 = A, 2 = B). P-codes that repeat lock out as H4/H5/H6/H9 and need power reset.
You can safely switch the unit off at the switch, wait 5 minutes and switch on again. Don't open the unit, touch wiring or handle gas: these checks need a trained technician.
E0
Communication error between outdoor units (shown on slave)
What our technician checks
- Master address 0, slaves below 4. H1-H1, H2-H2 wiring between ODUs, shielded, no open/short. Check PCB chips seated, pins, moisture.
E1
Phase sequence reversed or phase loss
What our technician checks
- Phase sequence (auto-check only at first power-on). Loose power wire at terminals, lost phase.
E2
Communication error with indoor units (shown on master)
What our technician checks
- Check P-Q-E communication wire for open/short (measure resistance), daisy-chain (hand-in-hand) layout, shielding, distance from power cables, lamps/transformers nearby, wire length. All IDUs powered? Duplicate addresses? Voltage P/Q to E about DC 2.5 V (0 V or 5 V = 485 chip faulty).
E4
Outdoor ambient sensor (T4) error
What our technician checks
- Sensor connection to PCB
- sensor open/short.
E5
Voltage protection
What our technician checks
- Measure supply voltage, all phases, under load.
E8
Outdoor unit address error
What our technician checks
- ENC1 address must be 0-3. Check dial switch, 74HC165N chip, PCB connection wire.
xE9
S11 setting does not match capacity
What our technician checks
- S11 and ENC2 (capacity switch) must match the outdoor unit capacity.
xH0
Communication error between DSP (IR341) and main chip
What our technician checks
- Power supply / phase loss
- transformer on main board
- interference
- chip seating.
H1
Communication error between 0537 chip and main chip
What our technician checks
- 0537 chip, main chip, interference, pins, moisture.
H2also H3
Number of outdoor units decreased (main unit)
What our technician checks
- Signal wire between ODUs loose
- ODU addresses
- any ODU powered off
- all ODUs on unified power.
H3
Number of outdoor units increased (main unit)
What our technician checks
- Same as H2: signal wire, addresses, unified power.
H4
P6 inverter-module protection 3 times in 60 min
What our technician checks
- See P6 / L-codes. Press query button to read the L-code.
H5
P2 low-pressure protection 3 times in 60 min
What our technician checks
- See P2.
H6
P4 discharge-temp protection 3 times in 100 min
What our technician checks
- See P4.
H7
Number of indoor units decreased (IDU lost > 3 min)
What our technician checks
- Check P-Q-E communication wire for open/short (measure resistance), daisy-chain (hand-in-hand) layout, shielding, distance from power cables, lamps/transformers nearby, wire length. All IDUs powered? Duplicate addresses? Voltage P/Q to E about DC 2.5 V (0 V or 5 V = 485 chip faulty). IDU control board / 485 IC.
H8
High-pressure sensor error (Pc ≤ 0.3 MPa)
What our technician checks
- Sensor connector and supply
- compare with gauge.
H9
P9 DC fan protection 3 times in 60 min
What our technician checks
- See P9.
Hb
Low-pressure sensor open/short
What our technician checks
- Sensor connector, open/short.
xHd
Auxiliary (slave) outdoor unit error
What our technician checks
- x = which auxiliary unit (1Hd = aux unit 1). Read the code on that unit.
P0
Inverter compressor top temperature protection
What our technician checks
- Low charge / leak
- outdoor fan
- coil dirty
- ODUs too close (air short-circuit)
- too many IDUs
- air/N2 in system
- blockage on low side (frost).
P1
High-pressure protection
What our technician checks
- ODUs too close, fan broken, dirty coil, liquid pipe blocked, valve not opened, air/N2 in system, overcharge.
P2
Low-pressure protection (3× in 60 min → H5)
What our technician checks
- Lack of refrigerant/leak, gas pipe blocked, gas valve closed, EXV blocked, indoor fan not running, dirty indoor coil/filter.
xP3
Compressor current protection
What our technician checks
- Excess load, overcharge, poor outdoor heat exchange, air/N2, power wiring short. Compressor terminals 1-5 Ω between any two, infinite to earth.
P4
Discharge temperature protection (3× in 100 min → H6)
What our technician checks
- Same as P0: low charge, airflow, air in system, blockage.
P5
High condenser temperature protection
What our technician checks
- T3 sensor connection
- excess load
- poor outdoor heat exchange
- air/N2
- liquid-side blockage
- outdoor fan motor.
xP6
Inverter module protection (3× in 60 min → H4)
What our technician checks
- Press query button within 1 min to read the L-code (L0-L9) and follow it.
P9
DC fan module protection (3× in 60 min → H9)
What our technician checks
- Control box / ambient too hot, fan module heatsink, wires between fan module and main PCB, P-N voltage on module, fan motor blocked. Swap module into another ODU to test.
xL0
DC compressor (inverter) module error
What our technician checks
- Compressor U-V-W 0.9-5 Ω each pair and equal, infinite to ground. Module: P-N = 1.41 × supply
- terminals 1-2 = 510-580 V DC. With 3,4,5 disconnected, all terminal pairs infinite (≈0 = module damaged). DC bus wire direction through inductor must follow arrow.
xL1
DC bus low voltage protection
What our technician checks
- DC 1-2 terminals 510-580 V. Below 510 V: check rectifier wiring for looseness.
xL2
DC bus high voltage protection
What our technician checks
- DC 1-2 above 580 V: measure across the two electrolytic capacitors (510-580 V, meter on 1 kV range)
- check supply too high / unstable.
xL4
MCE error / synchronisation / closed loop
What our technician checks
- Same as L1: DC bus 510-580 V, rectifier wiring, module and circuit.
xL5
Zero speed protection
What our technician checks
- Electric circuit and compressor.
xL7
Phase sequence error (compressor)
What our technician checks
- Module and U/V/W wiring order.
xL8
Speed change > 15 Hz within one second
What our technician checks
- Compressor U-V-W 0.9-5 Ω, infinite to ground. Swap test: run compressor from a healthy system's control box (U,V,W in order).
xL9
Set vs actual speed differs > 15 Hz
What our technician checks
- Same as L8.
Code not here, or still showing?
Send a photo of the display and the model sticker on WhatsApp. We'll tell you what it means and whether it needs a visit.
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