Carrier LED Blink Codes

Outdoor unit contactor is not pulling in.

• Bad contactor
• No 24V signal from thermostat
• Low voltage transformer failure

1. Check 24V signal at contactor coil
2. Test contactor coil for continuity
3. Inspect thermostat subbase wiring

Furnace has reached maximum retry attempts for ignition or flame proving and has locked out.

• Ignition failure after 3 attempts
• Flame sensor cannot prove flame
• Gas supply interrupted

1. Power cycle furnace to clear lockout
2. Clean flame sensor with fine steel wool
3. Verify gas supply is on
4. Check igniter for cracks or wear

System is in standby with no call for heat. LED pulses slowly as a heartbeat indicator.

1. No action needed - normal standby operation

System locked out on high head pressure.

• Dirty condenser coil
• Blocked airflow around outdoor unit
• Overcharge of refrigerant
• Non-condensables in system

1. Clean condenser coil
2. Clear debris around unit (36 inch clearance)
3. Check refrigerant charge
4. Check condenser fan motor operation

Pressure switch is reading closed before the inducer motor starts. Switch may be stuck or wiring issue.

• Stuck pressure switch contacts
• Inducer motor running when it shouldn't
• Short in pressure switch wiring

1. Disconnect pressure switch hose - switch should open
2. Test pressure switch with multimeter
3. Check for inducer running inadvertently

System has received a call for heat and is operating normally.

1. No action needed - system is heating

System locked out on low suction pressure.

• Low refrigerant charge (leak)
• Restricted liquid line
• Dirty evaporator coil
• Failed TXV/EEV

1. Check refrigerant charge and look for leaks
2. Inspect liquid line filter drier
3. Check evaporator coil
4. Test expansion valve operation

Inducer is running but pressure switch has not closed within the expected time.

• Blocked flue/exhaust pipe
• Blocked condensate drain
• Cracked or disconnected pressure hose
• Weak inducer motor
• Bad pressure switch

1. Check flue and intake pipes for blockage (ice, birds, debris)
2. Inspect pressure switch hose for cracks or disconnection
3. Clear condensate drain/trap
4. Measure inducer motor amps
5. Test pressure switch actuation

The high temperature limit switch has tripped due to excessive heat in the heat exchanger.

• Dirty or clogged air filter
• Blocked return air vents
• Failed blower motor
• Blower running too slow
• Oversized gas orifices

1. Replace air filter immediately
2. Ensure all return and supply vents are open
3. Test blower motor operation and speed
4. Check gas manifold pressure
5. Inspect limit switch reset

Control board is detecting flame when the gas valve should be off. Potential gas leak.

• Gas valve leaking through internally
• Short circuit in flame sensing circuit
• Control board malfunction

1. SAFETY: Turn off gas supply immediately
2. Test gas valve for leak-through
3. Inspect flame sensor wiring for shorts
4. Replace gas valve if leaking

The furnace detected a power interruption or low voltage condition on the 24V control circuit.

• Power flicker or outage
• Loose wiring connection
• Weak transformer
• Thermostat wire short

1. Check 24V transformer output
2. Inspect all wire connections for looseness
3. Look for thermostat wire damage
4. Check for proper line voltage

The control board cannot properly energize the gas valve circuit.

• Failed gas valve coil
• Bad wiring to gas valve
• Control board gas output failure

1. Test gas valve coil resistance (should be 40-200 ohms)
2. Check wiring between board and gas valve
3. Test voltage output from board to gas valve
4. Replace gas valve if coil is open

The hot surface igniter or its circuit has failed.

• Cracked hot surface igniter
• Open igniter circuit
• Board igniter output failure
• Loose igniter connection

1. Test igniter resistance (normal: 40-200 ohms at room temp)
2. Inspect igniter for visible cracks
3. Check wire connections at igniter and board
4. Replace igniter if open or cracked

Line voltage polarity is reversed or ground is missing.

• Hot and neutral wires reversed at outlet
• Missing or broken ground wire
• Incorrect wiring at disconnect

1. Check outlet with polarity tester
2. Verify hot, neutral, and ground connections
3. Correct polarity at electrical panel if needed

The flame rollout safety switch has tripped, indicating flames escaping the combustion chamber.

• Cracked heat exchanger
• Blocked heat exchanger passages
• Excessive gas pressure
• Rollout switch failure

1. STOP - Potential carbon monoxide hazard
2. Inspect heat exchanger for cracks visually
3. Check gas manifold pressure
4. Do NOT just reset the rollout switch without finding the cause
5. Test CO levels in supply air