HVAC Troubleshooting: How to Troubleshoot Your HVAC System

October 22, 2009

It’s always a good idea to understand the problems your HVAC system might experience and how you might be able to troubleshoot HVAC issues before calling a technician. You can often catch a problem early by simply scheduling regular maintenance and checking things like your filter, thermostat, or outdoor unit.

At A.J. Perri, we want to help you feel confident handling simple fixes on your own. That’s why we’ve put together this HVAC troubleshooting guide to walk you through the most common steps, what to check first, and how to know when it’s time to schedule professional service.

Table of Contents

• The Most Common Heating and Cooling Problems
• Troubleshooting Your HVAC
  • Check Thermostat Settings
  • Inspect Circuit Breakers
  • Check the Air Filter
  • Inspect Vents and Ducts
  • Inspect the Outdoor Unit
  • Reset Your HVAC System
• Smart Thermostat Diagnostics
• Seasonal HVAC Troubleshooting Tips
• Winter Issues
• Summer Issues
• HVAC Troubleshooting Chart
• What Not to Do: When to Call a Professional

The Most Common Heating and Cooling Problems

Understanding what typically goes wrong with your heating and cooling system can help you take action more quickly and possibly prevent a minor issue from becoming a major repair. Whether it’s the furnace in winter or your A/C in summer, many problems start with similar symptoms. Think of this as your quick-reference HVAC troubleshooting cheat sheet for identifying potential causes of poor performance or comfort issues.

• Lack of maintenance: Lack of maintenance is one of the leading causes of unexpected breakdowns, poor comfort, and higher energy bills. Regular maintenance services can save a lot of money in the long run.
• Dirty or clogged filters: This affects both heating and cooling. A clogged filter restricts airflow, reduces comfort, and puts extra strain on your system.
• Airflow problems: Whether caused by damaged fan motors, worn belts, or failed bearings, poor airflow can lead to overheating of the furnace or reduced air conditioning performance.
• Thermostat malfunctions: These issues can cause your system to shut off prematurely, run constantly, or fail to respond, leaving your home excessively hot or cold.
• Ignition or pilot light issues: Often, this can cause intermittent or no heat in furnace systems. In gas systems, this can also be a safety concern.
• Refrigerant leaks: Common in A/C units. Low refrigerant leads to weak cooling and can eventually damage the compressor.
• Frozen evaporator coils: Usually caused by poor airflow or low refrigerant levels. Frozen coils can lead to a complete loss of cooling.
• Dirty condenser coils: When your outdoor unit is covered in dirt or debris, it can’t release heat effectively, making your A/C work harder for worse results.
• Sensor or electrical control failures: Wear and tear on wiring or sensors can cause the system to short-cycle or fail to respond to settings.

Many of these issues build over time and could have been prevented with regular checkups. Knowing what to watch for gives you a major advantage as a homeowner and helps you speak confidently when you do need to schedule professional service.

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Troubleshooting Your HVAC

Some HVAC issues are easy to fix with a quick check; others may require professional attention. Start with the steps below to rule out simple problems before scheduling service. And if your system isn’t working at all or you’re dealing with something urgent, call A.J. Perri at 732-733-2541 for emergency HVAC support.

Check Thermostat Settings

Start here—this is always the first thing to check when your HVAC system isn’t turning on or responding. Make sure the thermostat is set to “Heat” or “Cool,” depending on the season, and that the fan is switched to “Auto” or “On.” Try adjusting the temperature a few degrees above or below the current room reading to see if the system kicks on.

Inspect Circuit Breakers

If your thermostat settings look correct, the next step is to check your circuit breaker box. Look for the breaker labeled for your heating and cooling system—it may have tripped, even if it appears to be “on.” Flip it fully off, then turn it back on to reset it. In some cases, a tripped breaker or blown fuse is all that is stopping your HVAC system from running.

Check the Air Filter

A dirty or clogged air filter is one of the most common causes of HVAC performance issues. If airflow is restricted, your system must work harder and may shut down entirely to prevent damage. Remove the current filter and check for dirt or dust buildup. If it looks clogged, replace it with a clean one and see if that restores airflow and comfort.

Inspect Vents and Ducts

Blocked vents are a common reason rooms feel too hot or too cold. Check that all supply and return grates are open and unobstructed by furniture, rugs, or curtains. If the openings are clear and airflow still feels weak, this could indicate a buildup or leak in your ductwork.

Rattling or banging sounds may also come from loose or shifting ductwork. Learning how to troubleshoot an HVAC system involves examining the entire airflow path, including vents, filters, and ducts, to identify issues that impact comfort, efficiency, and noise.

Inspect the Outdoor Unit

Your outdoor HVAC unit needs space and airflow to operate properly. Start by clearing away any leaves, grass clippings, or debris that may have collected around it. Clogged HVAC systems can quickly lead to overheating or reduced efficiency. Check for signs of damage, ice buildup, or anything blocking the fan. You’ll also want to make sure small animals haven’t taken up residence in your unit—keeping critters out of your HVAC system can help you avoid major surprises and expensive repairs down the line.

Reset Your HVAC System

If nothing else works, a full system reset may help. Start by turning off your thermostat, then switch the system off at the breaker. Wait about 30 seconds before turning everything back on. This can resolve minor electronic glitches or restore normal function after a brief power interruption. After resetting, allow your system a few minutes to boot up and listen for unusual noises or signs of trouble.

Smart Thermostat Diagnostics

If you have a programmable thermostat, check for the correct day and time settings to see if the system has entered a program period with an undesirable setting that needs modification. A small setting mistake can mimic a bigger problem.

Seasonal HVAC Troubleshooting Tips

Your HVAC system faces different demands depending on the time of year. Whether you're cranking up the heat or trying to stay cool, seasonal changes can expose specific weaknesses in your system. Use this as a quick seasonal reference within our larger HVAC troubleshooting guide to stay ahead of common problems and keep your system running smoothly year-round.

Winter Issues

• Furnace not turning on: Often caused by a tripped breaker, a dirty flame sensor, or a thermostat issue.
• Cold spots in the home: May indicate airflow problems or duct leaks.
• Frequent cycling: Can be caused by dirty filters, a failing thermostat, or an oversized system.
• Unusual smells (burning or musty): Might signal dust buildup, overheating, or trapped moisture.
• Ice buildup on the outdoor unit (for heat pumps): Often indicates defrost cycle issues or poor drainage.

Summer Issues

• Air conditioner not cooling: This could be due to low refrigerant, dirty coils, or a miscalibrated thermostat.
• Weak airflow: Often linked to clogged filters, blocked vents, or blower problems.
• Warm air coming from vents: May indicate a tripped breaker, frozen coils, or compressor trouble.
• Water leaking around the unit: Typically caused by a clogged condensate drain line.
• High indoor humidity: Can result from short cycling, oversized units, or malfunctioning dehumidification settings.

HVAC Troubleshooting Chart

If you’re not sure where to start, this quick-reference HVAC troubleshooting chart can help you identify symptoms, spot possible causes, and decide what steps to take next.

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When to Call a Professional

While this HVAC troubleshooting guide can help you fix minor issues, not every problem is safe—or smart—to tackle on your own. Some situations require specialized tools, training, or access to parts that the average homeowner doesn’t have. Trying to DIY repair certain HVAC components can lead to more damage, higher repair costs, or even personal injury.

If you notice any of the following, it’s time to step back and call a licensed professional:

• Electrical issues such as burning smells, flickering lights, or repeated breaker trips
• Refrigerant problems, including frozen coils, hissing noises, or visible leaks
• Strange odors, especially gas or burning smells, coming from your vents or unit
• Visible water leaks from the indoor unit or near the furnace
• No airflow at all, even after checking vents, filters, and settings
• Loud or abnormal noises like screeching, grinding, or banging
• Thermostat wiring problems or any need to replace hardwired components
• Failed ignitions or pilot light issues in gas furnaces
• Repeated system cycling that doesn’t respond to filter changes or resets
• Anything involving internal parts, such as blower motors, compressors, or capacitors

If your system shows any of these signs, or if you’ve gone through all the basic steps and things still aren’t working, it’s time to bring in a pro. Call A.J. Perri at 732-733-2541 for expert HVAC service you can trust.