Carrier Furnace & AC Error Codes Explained

When the system fails and you see a blinking LED or an error display on your Carrier furnace or AC, it isn’t just annoying—it’s a tech-level fault code telling you what’s wrong. We know that decoding these error alerts quickly can save you from burned-out motors, higher energy bills, and system breakdowns.

Below you’ll find a detailed breakdown of error codes for Carrier furnaces and for Carrier air conditioners (especially the “E3” code) with real-world explanation of what’s happening, what to inspect, and when you should call in a pro. If your blower motor is humming, burning up, or completely dead, you don’t have to guess part numbers. Head to unitedhvacmotors.com and we’ll help you match the correct motor fast.

Carrier Furnace Error Codes

Here are some of the key error-code patterns you’ll encounter with a Carrier furnace control board. We’re talking about the LED sequences of short and long flashes (e.g., 2 short / 3 long) and what they mean mechanically in the field.

Code 1-1 (1 short, 1 long) – No previous code

This code indicates that there is no previous fault recorded in memory. Essentially the control board has been reset (either power interrupted or control reset). You’re starting fresh. If you’re seeing this, it’s not the fault itself—it’s telling you there is no fault history. It’s a sign you’re at the beginning of diagnostics.

Code 1-2 (1 short, 2 long) – Blower runs after power-up during call for heat

In this scenario the blower is running for about 90 seconds after power is applied because the control detected that the unit was already asked for heat (R-W closed) at startup. Mechanically it means the blower motor is being commanded and the board is timing the post-power-up run. If everything else is normal after that then you’re okay. If the blower fails to run or runs erratically, you’ll want to check blower startup, capacitor, wheel condition.

Code 1-3 (1 short, 3 long) – Limit or flame roll-out switch lockout

This fault means a high-limit or rollout switch (safety device) has opened, locking the furnace out. Commonly caused by restricted airflow (dirty filter, closed return/supply vents), blocked secondary heat exchanger, or flame rollout due to venting problem. In practice we’ve seen blower motors working, but airflow low and limit switch opening fast. Fix the airflow or venting first before swapping parts.

Code 1-4 (1 short, 4 long) – Ignition lockout

This means the furnace attempted ignition a set number of times and failed, then locked out. Typical issues are failed hot­surface ignitor, cracked flame sensor, low gas pressure, poor flame carryover, gas valve issues.

Code 2-1 (2 short, 1 long) – Gas heating lockout

In this case the control board will not auto-reset. The furnace detected a sustained fault in the gas-heating circuit: bad gas valve, wiring issue, or defective control. It’s more than a simple limit switch opening. If you see this, it’s time for deeper diagnostics on the burner assembly, gas train, control board.

Code 2-2 (2 short, 2 long) – Abnormal flame-proving signal

This means the flame sensor proved flame when it shouldn’t have (gas valve de-energized) or the signal is erratic. Possible causes include a stuck-open gas valve, burned-out flame sensor, wiring short, or control board fault. In field work we sometimes remove the flame sensor, clean it with scotch-brite, and it clears this fault—if wiring and gas pressure are okay.

Code 2-3 (2 short, 3 long) – Pressure switch didn’t open

The inducer motor started, but the pressure switch didn’t open as expected. Could mean blocked vent pipe, bad inducer motor, defective pressure switch, or tubing kinked/blocked. We’ve pulled ductwork only to find bird nests or blocked PVC venting causing this exact code.

Code 2-4 (2 short, 4 long) – Secondary voltage fuse is open

This is an electrical fault in the control circuit – the secondary side fuse (often 3 A) on the board is blown, meaning there’s a short in that secondary wiring or board. Must check wiring, board, insulation, and ensure nothing is contacting the chassis.

Code 3-1 (3 short, 1 long) – Pressure/draft safeguard/aux-limit switch didn’t close (or reopened, down-flow only)

The furnace is essentially detecting that after startup the draft/pressure circuit didn’t close in time or reopened during operation. Could be related to inducer motor voltage, vent sizing inadequate, blower motor issue (dragging wheel), or restricted vent. In attics we’ve felt the inducer get hot from overwork under this fault.

Code 3-3 (3 short, 3 long) – Limit or flame roll-out switch is open (after 3 minutes)

This is similar to 1-3 but triggered after a few minutes of operation. It means the high limit or rollout device opened during operation. I’ve seen this when blower motors are failing, ducts collapsing, returning airflow throttled, leading to overheating.

Code 3-4 (3 short, 4 long) – Ignition proving failure

In this condition the furnace attempted ignition and flame was not sensed within the proving period. Then repeated tries and locked out. You’ll want to check the flame sensor, ignitor, valves, wiring, and ground.

Code 4-1 (4 short, 1 long) – Blower outside valid speed range

This tells us the blower motor speed feedback (in ECM or PSC) is outside what the control expects. Could be blower wheel drag, dirty wheel, worn bearings, motor slipping, bad capacitor, or motor itself failing. I’ve replaced a blower motor mid-winter because this code kept happening every start-up.

Code 4-2 (4 short, 2 long) – Inducer outside valid speed range

This indicates the inducer motor or its control is not running at expected speed. Could be weak inducer motor, failing bearings, impeller damage, or wiring/voltage issue. We once found a squirrel had shoved nesting material into the inducer housing, slowing it and triggering this code.

Code 4-3 (4 short, 3 long) – Pressure switch calibration faulty

The pressure switch/hose/venting circuit is out of spec; common causes include condensate trap water backing up, vent pipe collapse, or vent motor shaft tilting. In these cases the fix was clearing the trap and verifying vent pipe integrity.

Carrier AC / Heat Pump Error Codes

When your Carrier split-system air conditioner or heat pump shows something like “E3” on the indoor or outdoor unit display or remote, this is usually not a simple thermostat blip. It often points to fan speed, sensor or communication faults. These codes require a careful tech check because ignoring them can lead to motor failure, compressor damage or inefficient cooling.

Code E3 – Indoor unit: “Indoor fan speed has been out of control”

If you see E3 on the indoor unit, it means the motor or fan controller detected the indoor blower is running either too slow or too fast, outside of expected parameters. The blower is responsible for pulling air over the evaporator coil at the correct CFM; if that falls out of spec, you’ll lose performance or risk coil icing and higher static pressure. In the field we find this when the blower motor bearings are shot, the wheel’s covered in lint, capacitor weakened, or wiring/feedback tachometer lead broken.

Code E3 – Outdoor unit: “Communication malfunction between IPM board and outdoor main board”

On some Carrier outdoor units the same code E3 means communication failure between the IPM (intelligent power module) board and the outdoor main board. That means the inverter compressor/extreme load system is not receiving valid signals. It could be a wiring fault, poor connector, board failure, or overheating of the IPM module. Although it’s labelled the same code, the physical location and component suspected differ.

What to Do When You Encounter These Codes

When you’ve got a code flashing and the system is acting up, follow the practical tech steps we walk through on service calls. First, make it safe. Turn off power. Do not assume the system is “just broken” in a benign way. Overheating motors, locked rotors, blocked vents, and gas faults can lead to bigger issues.

If you’re comfortable doing some of the inspection yourself: check and replace your air filter, ensure all supply and return vents are open, check for visible debris or blockage in intake/exhaust vents, check for blown breaker or tripped disconnect, look at blower wheel and motor to see if dusty, wheels loose or wobbling, listen for strange bearings noise, check blower motor amps vs spec, inspect control board for burnt marks, check wiring harnesses for loose connections. If the code repeats after these checks, you’re looking at component failure (motor, board, pressure switch, inducer) and you’re at the point where a trained technician should intervene.

For any blower-motor specific issue (for example Code 4-1 on a furnace or indoor unit E3 fault on AC), we at unitedhvacmotors.com stock proper matched replacement motors, direct support and can help you pick the correct part number to avoid the wrong motor installed, wrong speed, wrong voltage. Don’t guess at the motor and cause imbalance, high static, premature failure.

Summary 

When your Carrier system is throwing one of these codes, you now know what component is likely at fault, what to check, and roughly how urgent it is. You’re no longer flying blind. If you need help identifying the exact motor, control board, or component matched to the fault code, visit unitedhvacmotors.com and tell us your model number. We’ll help you get the right motor shipped fast so your system can breathe again.