Furnace Troubleshooting Techniques You Need to Know

February 19, 2025

When your air conditioner suddenly stops keeping your home cool, it’s not just an inconvenience—it can disrupt your entire day, especially during Indiana’s and Lower Michigan’s hot and humid summer months. While some HVAC issues require professional repair, many common problems start small and can be caught early with a little know-how.

In this air conditioning system troubleshooting guide, we’ll walk you through the most frequent repair issues homeowners face, how to identify them, and when it’s time to call in the experts. Whether you’re a DIY-savvy homeowner or simply looking to stay informed, this guide helps you recognize warning signs and understand what your system is telling you.

1. Your AC Isn’t Cooling Properly

Possible Causes:

Dirty Air Filter: One of the most overlooked culprits. A clogged filter restricts airflow, reducing system efficiency and cooling capacity.
Thermostat Issues: If your thermostat isn’t working correctly, has dead or weak batteries, or is placed in direct sunlight, it may misread the indoor temperature and cause your AC to run inefficiently.
Low Refrigerant Levels: A refrigerant leak can prevent your system from absorbing enough heat from your home.

Troubleshooting Tips:

Check and replace your air filter monthly during peak cooling seasons.
Make sure your thermostat is set to “cool” and placed away from heat sources.
If air is blowing but not cold, contact a professional to check for refrigerant leaks—this requires handling by an EPA-certified technician, and all of Goff’s service experts meet this certification standard.

⚠️ Refrigerant Handling Warning:

Federal law prohibits anyone without proper EPA Section 608 Certification from handling refrigerants like R-410A. This includes checking, refilling, or repairing refrigerant lines. Improper handling not only poses serious health and safety risks—including frostbite, respiratory issues, or chemical burns—but can also damage your AC system and violate environmental regulations.

All Goff Heating and Air Conditioning service technicians are certified and trained to safely handle refrigerants in compliance with EPA standards. If you suspect a refrigerant leak or your system isn’t cooling properly, call our team for professional service you can trust.

2. AC Won’t Turn On

Possible Causes:

Tripped Circuit Breaker: Power surges can trip the breaker connected to your AC unit.
Blown Fuse or Faulty Wiring: Electrical issues can prevent the system from powering on.
Thermostat Malfunction: A dead battery or misconfigured settings can prevent startup.

Troubleshooting Tips:

Reset your circuit breaker and see if the system powers up.
Replace the thermostat batteries and double-check your settings.
If your system still doesn’t respond, schedule a diagnostic service with a licensed HVAC technician.

3. Strange Noises from Your AC

Common Sounds and What They Mean:

Banging or Clanking: Could indicate a loose or broken part, such as a connecting rod or piston.
Buzzing: Often signals electrical issues or a failing motor.
Squealing: Worn-out fan belts or motor bearings are usually to blame.

Troubleshooting Tips:

Turn off your system immediately if you hear banging or grinding to avoid further damage.
Schedule a repair visit to have internal components inspected.

4. Water Leaks or Excess Moisture

Possible Causes:

Clogged Condensate Drain Line: Dirt and debris can block the drain, causing water to back up into your home.
Frozen Evaporator Coil: Low refrigerant or airflow issues can cause the coil to freeze and melt.

Troubleshooting Tips:

Clear any visible debris near the drain line or pan.
If the leak persists or ice is present, it’s time to contact Goff Heating and Air Conditioning for service.

5. Weak Airflow

Common Causes:

Ductwork Leaks: Air may be escaping through cracks or disconnections in your ductwork.
Fan Issues: The blower fan may be dirty or malfunctioning.
Aging System: Older units naturally lose efficiency over time.

Troubleshooting Tips:

Replace air filters and check vents for obstructions.
Have your ductwork inspected as part of your bi-annual GoffCare Maintenance Membership.

6. Frequent Cycling On and Off

Potential Causes:

Oversized System: An AC that’s too large for your home will short cycle.
Dirty Components: Dirty filters or coils make your system work harder and cycle more often.
Thermostat Problems: Faulty sensors may misread indoor temps.

Troubleshooting Tips:

Clean your unit regularly or sign up for a GoffCare Membership for professional tune-ups.
Contact a Goff technician to evaluate if your system is properly sized for your home.

7. High Energy Bills

Why It Happens:

Inefficient Equipment: Older AC units draw more power to deliver the same performance.
Poor Maintenance: Dirty coils, clogged filters, and low refrigerant reduce efficiency.
Leaky Ducts: Up to 30% of cooled air can escape through leaks.

Troubleshooting Tips:

Schedule an energy audit or performance check.
Consider upgrading to a high-efficiency Bryant system installed by Goff, a Bryant Factory Authorized Dealer and 2024 Circle of Champions award recipient.

8. Electrical Component Failures

Common Issues:

Capacitors Out of Spec: The capacitor is like a battery that helps your AC motor start and run efficiently. Over time, it can degrade or go out of spec, causing your system to struggle or fail to start altogether.
Failing Contactors: Contactors are electrical switches that control the flow of electricity to your system’s components. When they wear out, you might notice a humming sound, intermittent operation, or the unit not turning on at all.

⚠️ Important Safety Warning:

We strongly advise homeowners not to attempt to test or replace capacitors or contactors on their own. These components store high voltage and can deliver dangerous electric shocks, even when the system is powered off. This work should only be performed by trained HVAC professionals—like our skilled technicians at Goff Heating and Air Conditioning.

Troubleshooting Tips:

If your AC isn’t starting, is making unusual clicking or humming noises, or is randomly shutting down, it’s likely time for a professional inspection.
Goff’s technicians are equipped to safely test and replace these critical electrical components, getting your system back up and running fast.

Prevent Common Repairs with GoffCare

A majority of AC repairs stem from poor maintenance. That’s why Goff Heating and Air Conditioning offers the GoffCare Maintenance Membership, designed to prevent breakdowns before they happen.

GoffCare Membership Benefits:

Bi-Annual HVAC Tune-Ups
24-Hour Priority Service
Exclusive Discounts on HVAC Repairs
Extended Equipment Life

With GoffCare, you’ll stay one step ahead of unexpected repairs—and enjoy peace of mind all year long.

When to Call a Professional

While simple tasks like changing filters and checking your thermostat can be DIY-friendly, anything involving refrigerant, electrical components, or internal parts should always be handled by certified professionals.

At Goff Heating and Air Conditioning, we’ve proudly served South Bend and the surrounding communities since 1937. With over 85 years of experience, we’ve seen—and fixed—it all. Our licensed technicians are trained to diagnose and repair systems quickly, keeping your home cool and comfortable.

Final Thoughts: Know the Signs, Stay Cool

Understanding the early warning signs of air conditioning issues helps prevent small problems from becoming major repairs. Whether it’s a mysterious noise, reduced airflow, or rising energy bills, early intervention is key.

Use this Air Conditioning System Troubleshooting Guide to identify common repair issues—and trust Goff Heating and Air Conditioning to take care of the rest.

Ready to Schedule a Service or Learn More About GoffCare?

Give us a call today or schedule your free consultation online. Our team is here to deliver the Quality You Trust. Service You Deserve. Since 1937.

When the temperatures drop in South Bend, Mishawaka, Granger, and Elkhart, a reliable furnace is crucial for keeping your home warm and comfortable. But what happens when your furnace starts acting up? Before calling a professional, there are several furnace troubleshooting techniques you can try to diagnose and potentially fix the issue.

This troubleshooting guide for your furnace will walk you through common furnace problems and solutions, helping you determine when a quick fix will do the trick and when it’s time to call an expert.

1. Check the Thermostat First

A malfunctioning or incorrectly set thermostat is one of the most overlooked furnace problems. Before assuming there’s a major issue, take the following steps:

Ensure the thermostat is set to “HEAT.”
Confirm the temperature is set higher than the current room temperature.
If your thermostat has batteries, replace them.
Make sure the fan setting is on “AUTO” instead of “ON.”

If the thermostat screen is blank or unresponsive, it may need replacement or rewiring.

2. Inspect the Air Filter

A clogged air filter is one of the most common reasons a furnace stops heating effectively, as it restricts airflow, causing the system to overheat and shut down prematurely. In fact, this is one of the most frequent emergency calls we receive, and more often than not, the solution is as simple as replacing a dirty filter. A dirty filter can:

Restrict airflow, causing the furnace to overheat and shut down.
Force the system to work harder, increasing energy bills.
Reduce indoor air quality by circulating dust and allergens.

Solution: Check your air filter monthly and replace it every 1-3 months, especially during peak heating season.

3. Verify the Power Supply

If your furnace won’t turn on at all, it might not be getting power. Try these furnace troubleshooting techniques:

Check the circuit breaker – if it has tripped, reset it.
Inspect the power switch near the furnace – it should be in the “ON” position.
If you have a gas furnace, make sure the pilot light or ignition system is functioning.

If power issues persist, a professional inspection may be required.

4. Pilot Light or Ignition System Issues

For gas furnaces, the pilot light or ignition system plays a crucial role in heating. If your furnace is not igniting, the issue may stem from:

A dirty or broken thermocouple, preventing the pilot light from staying lit.
A clogged ignition system that requires cleaning.
A faulty electronic ignition sensor that needs professional servicing.

If you’re comfortable, you can try relighting the pilot light by following the manufacturer’s instructions. However, if you suspect a gas leak or smell rotten eggs, evacuate your home immediately and call your utility provider. You should also contact a trusted HVAC company to inspect your system and ensure it is safe to operate.

5. Furnace Is Running but No Heat Is Coming Out

If your furnace turns on but doesn’t produce heat, there could be a few different causes:

Dirty burners – If the burners are clogged, they won’t generate heat effectively.
Gas supply issues – If there’s a disruption in the gas supply, the furnace won’t be able to produce heat. A professional technician should inspect and address any gas-related concerns.
Faulty heat exchanger – A cracked heat exchanger can reduce efficiency and may need replacement.

For these issues, the best solution is to have a professional HVAC technician diagnose and resolve the problem to ensure your furnace operates safely and efficiently. If heating problems persist, expert furnace troubleshooting will be necessary to identify and fix the issue.

6. Short Cycling – Furnace Turning On and Off Too Frequently

Short cycling occurs when a furnace turns on and off in quick cycles, preventing the home from reaching the desired temperature. Causes may include:

Overheating due to a clogged filter
A malfunctioning thermostat
Blocked vents restricting airflow
A faulty flame sensor

Solution: Start by replacing the air filter, ensuring vents are open, and checking the thermostat settings. If the issue continues, schedule a professional inspection.

7. Unusual Noises Coming from the Furnace

A properly functioning furnace should operate quietly. If you hear unusual sounds, here’s what they might indicate:

Banging or booming – Delayed ignition or dirty burners.
Rattling – Loose panels or components.
Squealing or screeching – Worn-out blower motor or belt.
Humming – An electrical issue with the motor or transformer.

Tightening loose parts, lubricating moving components, or cleaning the burners can sometimes resolve the issue. However, if noises persist, a professional furnace diagnostic will be needed.

8. Furnace Blower Keeps Running Nonstop

If your furnace blower motor won’t turn off, it could be due to:

A stuck fan limit switch, requiring manual adjustment or replacement.
The thermostat fan setting being set to “ON” instead of “AUTO.”
An internal control board issue that requires professional attention.

Try switching the thermostat to “AUTO” first. If the problem continues, it may be time for furnace repair.

9. Cold Spots or Uneven Heating in Your Home

If some rooms feel warm while others remain chilly, the problem may lie in your ductwork or airflow distribution. Possible causes include:

Leaky or disconnected ductwork that prevents warm air from reaching certain areas.
Blocked vents or registers that need to be cleared.
A failing blower motor that isn’t distributing air evenly.

A professional duct inspection can identify leaks and improve your home’s comfort.

10. High Energy Bills Without a Clear Cause

If your heating bills have suddenly spiked without any changes in your usage, your furnace may be losing efficiency. Common culprits include:

A dirty air filter forcing the system to work harder.
Aging furnace components reducing overall efficiency.
Leaky ductwork wasting heated air.

Regular furnace maintenance can help prevent these issues and lower energy costs.

When to Call a Professional for Furnace Repairs

While DIY furnace troubleshooting techniques can resolve some minor issues, there are times when professional service is necessary. Contact an HVAC expert if:

The furnace refuses to turn on despite checking the power and thermostat.
You smell gas or suspect a leak.
The system is making loud or unusual noises.
There’s weak or no airflow from the vents.
The furnace is short cycling or overheating.

Prompt repairs can prevent small issues from turning into costly breakdowns.

Get Professional Furnace Repairs in South Bend, Mishawaka, Granger & Elkhart

If you’re experiencing heating problems, Goff Heating & Air Conditioning is here to help! Our team specializes in diagnosing common furnace problems and solutions, ensuring your system runs efficiently throughout Indiana’s harsh winters.