How to Diagnose Common HVAC Problems

When your HVAC system isn’t performing at optimal levels, you notice it right away. A lack of cool air in the summer, a lack of warm air in the winter, or just no air coming out of the vents at all. How can you tell when the problem is easy to fix, and when should you call a professional?

Diagnosing Common HVAC Problems

Some HVAC problems are common and easy to diagnose. When that’s the case, you may be able to fix the problem yourself.

Poor Airflow

When your HVAC cooling system is running, but you notice little airflow from the vents, it’s a clear sign of an underlying issue. 

The cause could be any of the following:

  • Outside Unit Blockage: The fans of your outside unit might be obstructed by dirt, buildup, or debris.
  • Dirty Air Filters: These hinder proper airflow, straining your system.
  • Blower Fan Buildup: Accumulated dirt on the blower fan can significantly reduce its performance.


Regularly replace your filter to maintain the efficiency and lifespan of your unit. A clogged filter forces your unit to exert more effort in circulating air, leading to unnecessary strain on the blower. Also, inspect the filters for any signs of clogging, damage, or incorrect sizing. These issues can impede airflow, causing extra stress on the system and hindering proper air circulation.

Unusual Furnace Noises

All furnaces make some noise, but if you hear something unusual, like a high-pitched whining or grinding, you may have a problem.


Start by inspecting your unit’s inducer and blower motors. If bearings appear worn or damaged, you may need a new furnace. Ensure that burners are clean and debris-free, as this can often be a source of unusual sounds.

Hot & Cold Spots

Uneven temperature distribution in your space, known as hot and cold spots, often arises from airflow or air circulation issues.


Ensure that your ductwork is properly sealed. Leaks in the ducts can significantly impact the efficiency of your HVAC system, leading to uneven temperature distribution. You can also try a zoned heating and cooling system, each with its customizable temperature settings. This is controlled centrally from a thermostat. The system utilizes dampers within the ductwork to efficiently direct air to different areas.

Unit Doesn’t Turn On

Any number of things may keep your HVAC unit from turning on. These include:

  • Blown fuses
  • Tripped breaker
  • Dead or malfunctioning batteries
  • Wiring problems
  • Malfunctioning motors
  • A power outage


If the other electronics in your home have shut down, chances are there’s a power outage. Your local electric company may be able to tell you when the power will be back online.

If the problem isn’t a power outage, check that the batteries in your thermostat are working. They may simply need to be replaced. Finally, carefully check for disconnected wires in your system – outdoor units are particularly vulnerable. However, do not handle exposed wires yourself. Call a professional HVAC repair company to come and fix the problem.

Blown Fuses or a Tripped Circuit Breaker

When your furnace trips a circuit breaker or blows a fuse, it’s often due to the blower working too hard because something obstructs the airflow. When the filter is clogged, the blower struggles to push air through it, leading to increased energy consumption and, in some cases, a tripped circuit breaker. Begin by checking and replacing the filter with a clean one before resetting the breaker. 

Other factors include duct leaks, closed or obstructed air registers, or dirty coils.


First, locate the fuse box and inspect the breakers. Check if any are flipped in a different direction than the rest. Both the furnace and the air-conditioning unit should have separate labeled breakers.

If the breakers appear normal, toggle the switch for the unit experiencing issues. Allow about 10 seconds before turning it back on. If you have fuses instead, switch off the main power to the box and replace any blown or burnt fuses.

Higher Than Usual Energy Bills

If you notice a significant spike in your bills, it may indicate HVAC issues. Even seemingly minor issues like dirty filters can force your system to work harder, leading to higher energy bills. 


High energy bills can be mitigated by trying the following:

  • System Replacement: If your system is over a decade old, consider replacing it with a modern, energy-efficient one.
  • Improve Home Insulation: Fix air leaks and drafts in your home to enhance airtightness. Seal the duct system to prevent energy loss, and add insulation to key areas like the attic and ducts.
  • Schedule Professional Inspection and Maintenance: Book an appointment with a reputable HVAC service like John C. Flood for a thorough inspection and preventive maintenance.

Water Leaks

Water leaks can occur if the drain lines become obstructed or develop cracks. Other potential leak sources may include the collector box, heat exchanger, or evaporator drain pan. 


Check if the drain lines are clogged or damaged. If so, they may need to be cleaned or replaced. You can take a proactive step by periodically pouring bleach down the drain to maintain its cleanliness. 

Call John C. Flood for HVAC Repair

No matter what’s wrong with your HVAC system, John C. Flood can fix it. We provide regular inspections and maintenance, troubleshooting for major issues, and emergency repairs 24/7. Our flat-rate pricing means you’ll never have to pay more for a middle-of-the-night HVAC emergency!

We’re the #1 HVAC service provider in the Maryland, DC, and Virginia areas. Call now at 703-214-5611 for same day service!

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