carrier furnace

When addressing issues with Carrier furnaces, a thorough examination of each component is essential to determine the root causes and implement effective solutions. In this article, we’re looking at a detailed step-by-step guide that details the diagnostics and solutions for common problems encountered with Carrier furnaces, tailored to help both experienced DIY enthusiasts and professionals seeking a structured troubleshooting process.

Initial Diagnostic Steps

Get the following tools ready to use before beginning the troubleshooting process:

  • Multimeter: Essential for testing electrical parts
  • Screwdriver set: Accessing internal sections requires a screwdriver set.
  • Flashlight: In low-light conditions, a flashlight can be a lifesaver for visual inspections.
  • Cleaning brush or vacuum: To keep everything clean and free of debris, use a cleaning brush or vacuum.

By conducting a thorough first evaluation test, it is possible to avoid making repairs that are not necessary:

  • Exterior Review: A thorough inspection of the exterior of the furnace should reveal any signs of damage or wear and tear. Identify and repair any wires that are disconnected or loose.
  • Power Source Verification: Once the main power plug is switched on, the furnace will begin to operate. The input voltage should be checked using a multimeter to ensure that it agrees with the specific specifications of the furnace.
  • Thermostat Examination: Check the thermostat to determine whether or not increasing the temperature will result in the activation of the furnace. Put in fresh batteries if the ones that are already there are dead, and check to see that nothing is loose.

For the furnace to function effectively, it is necessary to have the appropriate airflow:

  • Filter Status: To inspect the air filter, remove it from its housing and examine it. To ensure that air can circulate freely, you should immediately clean or replace it if there is a significant amount of dirt accumulation or damage.
  • Ductwork Inspection: By inspecting the ducts for any signs of damage, bends, or disconnections, you can ensure that no obstructions are restricting the passage of air. To determine whether the ducts contain any dirt or obstacles, use a flashlight inside of them.

Furnace Fails to Start

When the thermostat is not functioning properly, it is possible for an incorrect diagnosis to occur:

  • Functionality Testing: Make use of a multimeter that is set to the continuity setting to examine the functionality of the thermostat. If it displays discontinuity, it might need to be replaced.

  • Calibration: It may be essential to calibrate the thermostat to obtain correct temperature readings and to ensure an appropriate level of communication with the furnace. For details on how to calibrate the thermostat, please refer to the handbook provided by the manufacturer.

Having the ignition system in place is essential to turn on the furnace:

  • Pilot Light and Electronic Ignition: If you are using an older model, you should also activate the pilot light in addition to the electronic ignition. Perform a thorough inspection of the ignitor, looking for any obvious signs of wear and tear. Additionally, on newer systems that are equipped with electronic ignition, search for error codes that could signal problems with the ignition system.

One possible cause of the inability to turn on the furnace is a problem with the wiring:

  • Connection Inspection: Verify that the connections and the connector are not overheated or corroding, and make sure that any loose wires are secured. Particular attention should be paid to ensuring that the connections on the control board are secure.

Furnace Operates but Does Not Heat

If there are issues with the gas line, the furnace will be unable to heat and will cool down your house instead:

  • Gas Valve Check: A multimeter should be used to check the functionality of the gas valve as well as the power supply. In addition to ensuring that the valve is open, check that the gas line is clear of any cracks or leaks.

Burners and a heat exchanger are both necessary components for the generation of heat:

  • Heat Exchanger Inspection: Be on the lookout for any cracks or holes in a heat exchanger when you are performing an inspection. The damage in question is often rather significant and may cause cooling instead of heating in your home, and you must seek the assistance of an HVAC professional.

  • Burner Check: Make sure that the burners are creating a blue flame that is consistent throughout. It is possible that the appliance has to be cleaned or adjusted if the flames cannot be described as yellow or uniform.

Issues with Frequent Cycling or Short Cycling

Thermostat Placement Considerations

When it comes to determining how a furnace will behave, the positioning of the thermostat is an important factor:

  • Optimal Placement: Maintaining the thermostat in an optimal position requires that it be kept away from drafts, direct sunlight, and sources of heat to provide the most accurate readings.

Adapting the Ductwork to the Size of the Furnace

It is possible for efficiency problems to occur when the size of the furnace and the ductwork are not compatible:

  • Size Evaluation: To ensure that the furnace is the appropriate size for the space, it is recommended that you consult with a heating specialist. On the other hand, if the furnace is too large, rapid cycling may occur.

  • Ductwork Compatibility: It is important to ensure that the ducting is of the suitable size to meet the output requirements of the furnace to achieve optimal performance.

Understanding how to optimize thermostat placement and adapt ductwork to furnace size is essential for maintaining efficient heating systems. Proper positioning and sizing ensure accurate temperature control and prevent performance issues.

Troubleshooting Unusual Noises

Blower Motor and Fan Assessment

There is a clear connection between the blower motor and the fan and the noise levels that they produce:

  • Blower Motor Evaluation: It is important to pay attention to any unexpected noises, such as screeching, because these sounds could be indications that an older system needs lubrication or requires a new generator belt.

  • Fan Inspection: Ensure that the fan blades are clean and aligned correctly to prevent any noise from the functioning of the fan. The fan speed should also be what it came with, not less or more.

Tightening Loose Internal Components

Securing internal components can significantly reduce noise during operation:

  • Component Security: Make sure that all of the screws and brackets on the interior of the component are securely fastened. This will ensure that the component is held in place.

Troubleshooting symptoms of a bad furnace unit control board

The control board or circuit board is generally something for HVAC professionals to troubleshoot. This is what they’ll generally do:-

  • Use the furnace’s wiring diagram to check for proper voltages at relays and output terminals.
  • Test the transformer and ensure the control board is receiving the correct low-voltage power.
  • Assess the microprocessor by checking the board’s ability to accept and process input from sensors and the thermostat.

Analyzing Error Codes in Carrier Furnaces

Interpretation: The unit records an absence of recent faults.

Rectification Approach: Any recorded issues will reset once the unit’s power cycle is interrupted.

Interpretation: Different scenarios are indicated here:

  • A. Post-ignition, the blower persists in operation (about gas units).

  • B. Calibration lockout is in effect for the blower (about electric units).

Rectification Approach: A. Normal operation for gas units involves the blower running for a brief period when the system initiates a heat cycle. B. An automatic recalibration is triggered if the blower’s RPM deviates from the expected range in electric units, typically resolving after 3 hours.

Interpretation: Activation of a limit switch or circuit lockout has occurred.

Rectification Approach: The system usually resets itself after a three-hour interval. Persistent issues warrant an examination similar to the one for Error 33.

Interpretation: A lockout due to ignition failure is in place.

Rectification Approach: Awaiting a 3-hour window often resolves this as the system resets. Should troubles continue, the process for Error 34 should be followed.

Interpretation: Varied based on the furnace type:

  • A. Lockout associated with gas heating mechanisms.

  • B. Misselection of the unit model in electric models.

Rectification Approach:

A. Manual intervention from a certified technician is requisite as auto-reset functions are inactive. B. Incorrect model configuration results in the system defaulting to the proximate airflow setting permissible.

Interpretation: Diagnostic results diverge between unit types:

  • A. Gas models report abnormal signals from the flame sensor.

  • B. Electric models indicate a configuration error within the setup switch.

Rectification Approach: A & B. Both scenarios necessitate the expertise of a certified technician.

Interpretation: Splits between gas and electric models: A. Gas models exhibit a failure in the pressure switch operation. B. Electric models have flawed blower airflow settings.

What should you do: A. Obstructions or damages in pressure-related components require inspection and potential professional intervention. B. Should the code present as a flashing signal, the system will align itself with the nearest suitable airflow configuration.

Interpretation: Indicates an open secondary voltage fuse, hinting at a short circuit potential.

Rectification Approach: Engaging with a certified technician is the recommended course of action.

Interpretation: A critical switch within the system failed to engage or disengage correctly.

Rectification Approach: Professional examination and repair are necessary as this may indicate a malfunctioning relay.

Interpretation: The fault lies with the low-pressure switch in the system.

Action Required:

  • For gas models, ensure there are no blockages in the vents or tubing. In the case of electric furnaces, verify that the condensate drain and vent piping are free of obstructions. If these checks don't yield results, a professional should be contacted.

Interpretation: There is an opening in the limit or flame roll-out switch.

Action Required: Conduct a thorough cleaning or replacement of the filter and remove any dust around the airflow inlets.

Interpretation: Failure in ignition proving has been detected.

Action Required:

  • The flame sensor may require cleaning. If the gas valve is at fault, ensure it's neither defective nor inadvertently turned off.

  • Should the problem continue, or if the code shifts to Error 14, professional service is necessary.

Interpretation: The blower is operating at a speed that is either too slow or too rapid.

Action Required: Professional diagnosis and service are recommended.

Interpretation: The inducer's operating speed is not within the expected range.

Action Required: Check for blockages in the condensate drain or venting. If all seems to be in order, yet issues persist, professional help should be enlisted.

Interpretation: A blockage or disconnection has caused an issue with the pressure switch.

Action Required:

  • For gas furnaces, look for and resolve any blockages or disconnections affecting the pressure tubing.

  • Electric furnace models should have the condensate drain and vent piping checked for similar issues.

  • If the issue is not resolved, it's advisable to contact a certified technician.

Interpretation: There is an issue with blower calibration; the blower speed does not align with the required specifications.

Action Required: Inspect and replace the filter if found necessary. If this error appears alongside Error 41, professional support is required.

Interpretation: The system's control has been locked out.

Action Required: Reset the furnace by turning it off and on. Should the error repeat, the expertise of an HVAC technician will be needed.

Carrier furnaces come equipped with LED indicators that provide visual feedback regarding the operational status of the unit. Here is a detailed explanation of the various signals these LEDs might display:

  • LED Off: This is typically an indication that the furnace is not receiving power. A good first step is to verify the voltage and ensure that the heater and furnace's electrical connections are secure and the power supply is on.

  • LED On Steadily: A non-blinking, steady light often suggests that the control panel or CCU board (just like how the APU starts in a cooling system) is energized and functional, and the furnace is not registering any issues that would interrupt its operation.

  • LED Blinking Rapidly: This pattern of signaling is usually a prompt that there could be a problem with how the circuit board of the furnace is wired, specifically a possible reversal in line voltage polarity or an issue with the grounding. Such conditions are serious and warrant prompt attention.

  • Solid Red on LED 1: This specific illumination often denotes that the furnace is in an alternative heating mode, typically referred to as emergency heat mode, which kicks in when the primary heating source is compromised or inoperative.

  • Solid Red on LED 2: This light generally points to a malfunction within the internal microprocessor. A reset of the system is commonly required to clear this type of fault.

  • Flashing Red on LED 2: A blinking light here mirrors the aforementioned issue concerning potential electrical wiring problems, specifically polarity reversal or grounding concerns that need to be corrected immediately.

  • Solid Yellow on LED 3: The presence of a solid yellow light usually indicates that the furnace is functioning at its higher heating capacity or is overheating to accommodate a greater need for warmth within the house or dwelling.

  • Solid Green on LED 4: A green light in this position typically signifies that the furnace is operating at a reduced heating level, often employed for maintaining a steady temperature or for gradually increasing warmth in the home environment.


How do you reset a Carrier furnace?

To reset a Carrier furnace:

  1. Turn off the power to the furnace at the breaker box.

  2. Wait a few minutes for the internal systems to power down.

  3. Turn the power back on. This general reset can resolve minor electronic glitches. For a more specific reset related to the blower motor or other components, you may need to consult your user manual for instructions related to your specific model.

What is the most common problem of a furnace?

The most common problem with furnaces, including Carrier models, tends to be issues related to air flow and heat production. This often stems from clogged air filters, problems with the thermostat settings, or issues connected with the ignition system or pilot light.

Why is my Carrier furnace not heating?

If your Carrier furnace is not keeping your home hot enough, it could be due to several reasons:

  • A dirty or dust-filled air filter restricts air flow.

  • Issues with the thermostat not communicating correctly.

  • A malfunctioning ignition system or a pilot light that won’t stay lit.

  • Inadequate gas supply or closed gas valves.

How do I reset my Carrier thermostat?

To reset a Carrier thermostat:

  1. Locate the “Reset” button on the thermostat. If it doesn’t have one visible, you might need to access the menu settings.

  2. If the thermostat is programmable, navigate through the menu options and look for a reset or restore factory settings option.

  3. Press and hold the reset button, or select the reset option, and confirm if necessary.

Why won't my Carrier thermostat work?

If your Carrier thermostat isn’t working, it could be due to:

  • Dead batteries.

  • Incorrect settings.

  • Issues in a wire that prevents it from communicating effectively with the furnace.

  • A malfunctioning sensor or internal component.

Where is the Carrier furnace reset button?

The reset button on a Carrier furnace is typically located on the side of the blower motor housing inside the furnace. You may need to remove a panel to access it. Look for a small red or yellow button.

Why Choose Comfort Union for your Carrier furnaces and more?

Exceptional Skill: Comfort Union’s technicians have extensive experience with Carrier systems and can handle any issue that arises. Thanks to their highly-trained and certified staff, your equipment will receive the best care possible, resulting in accurate diagnosis of problems and expert repairs that keep your system running smoothly.

Individualized Attention: At Comfort Union, we know that every room and system is unique, which is why we tailor our services to meet your specific needs. If you want your Carrier system to bring you the most possible comfort in your unique setting, you need our solutions, which are both effective and customized.

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