Fault codes
Flash codes, inverter errors, and the electrical faults that look like “bad compressors” until you meter them.
- 1 flashfurnace
Flame present, no call
IFC sees flame when it did not open the gas valve.
- Stuck gas valve
- Flame sensor wiring shorted to chassis
- Replace IFC if valve is closed and flame LED is still on
- 2 flashfurnace
Pressure switch closed on idle
Pressure switch is made before the inducer starts.
- Jumper left on the switch
- Welded switch
- Inducer still spinning from a previous call
- 3 flashfurnace
Pressure switch open on run
Inducer is on but the switch never closes, or drops out.
- Blocked flue / intake
- Cracked inducer housing
- Water in the hose
- Wrong hose on the switch
- 4 flashfurnace
Open limit / rollout
High limit or rollout opened the heat circuit.
- Dirty filter, closed registers
- Cracked heat exchanger (rollout)
- Over-fired manifold pressure
- Blower not coming on
- 6 flashfurnace
Ignition lockout
No flame sense after the allowed trials.
- Flame sensor dirty
- No gas at the valve (meter 24 V on a call)
- Ignitor ohms
- Polarity / poor ground
- E1 / E0mini-split
Communication error
Indoor and outdoor boards are not talking on wire 3.
- Ohm interconnect 1/2/3 — no shorts
- Voltage 1–2 per lid schematic
- Swapped 3 onto 1
- Shielded cable run next to line voltage
- E4 / F1mini-split
Indoor pipe / room sensor
NTC open, shorted, or out of range.
- Unplug sensor, read ohms vs temp chart
- Pinched sensor lead in the chassis
- Replace the thermistor before replacing the PCB
- P1 / P2mini-split
DC bus / IPM fault
Inverter over-voltage, under-voltage, or module overcurrent.
- Supply L1–L2 stable 208–230 V
- Reactor / PFC
- Compressor winding ohms U-V-W equal, no ground
- Do not megger through the IPM
- P4mini-split
Compressor drive fail
IPM could not start or hold the compressor.
- Locked compressor
- Winding imbalance
- Board output before condemning the compressor
- LPC / LPS lockoutrtu
Low-pressure lockout
Suction safety opened and the CCB latched.
- Charge, TXV, dirty filters, belt
- Reset: cycle unit power — confirm the switch is actually closed first
- HPCrtu
High-pressure lockout
Head pressure exceeded the switch.
- Dirty condenser, failed OD fan, overcharge, recirc on the roof
- CC no pull-inelectrical
Contactor will not pull in
Compressor and OD fan stay dark on a cool call.
- R–C 24–28 V
- Y–C 24 V at the outdoor
- 24 V before LPS/HPS, 0 V after = open safety
- 24 V at A1–A2 and no pull-in = open coil
- CC weldedelectrical
Contactor welded closed
Compressor runs with no Y call.
- Kill power at the disconnect
- Replace the contactor
- Find why it welded (shorted cap, hard start, low voltage)
- Cap outelectrical
Weak dual run capacitor
Hum, hard start, OD fan slow, compressor overheating.
- Power off, discharge, microfarad ±6% of rating on HERM and FAN
- Bulged can = replace
- No 24 Velectrical
Dead transformer
No R–C. Nothing on the control side will run.
- Door switch
- Primary voltage
- Fuse on R (if present)
- Shorted tstat wire — isolate R and retry