HVAC Troubleshooting Guide

HVAC Troubleshooting Guide

Before calling a technician, there are simple checks you can do yourself to fix common HVAC problems. This guide walks you through easy steps any homeowner can follow.

Preliminary Checks

Start here before doing anything else. These five checks solve most HVAC problems.

Thermostat

Your thermostat controls everything. Check these settings first:

• Make sure it’s set to the right mode: “HEAT” for warming, “COOL” for cooling
• Set the temperature at least 3-5 degrees above (for heat) or below (for cooling) the current room temperature
• Replace the batteries if the screen looks dim or blank
• If you have a programmable thermostat, check that the schedule hasn’t been changed accidentally

Power Supply

Your HVAC system needs electricity to run. If nothing turns on:

• Go to your electrical panel (usually in the garage, basement, or utility room)
• Look for any breakers that have flipped to the middle position or “OFF”
• If you find a tripped breaker, flip it fully to “OFF” first, then back to “ON”
• Wait 30 seconds before testing your system again

Air Filter

A dirty filter is the number one cause of HVAC problems. It blocks airflow and makes your system work harder than it should.

• Find your filter (usually behind a return vent or inside the air handler)
• Hold it up to the light. If you can’t see through it, replace it
• Standard filters should be changed every 1-3 months
• Write the date on the filter frame so you remember when you installed it

System Switch

Most furnaces and air handlers have a power switch that looks like a regular light switch. It’s usually mounted on or near the unit, often in a gray box.

• Make sure this switch is in the “ON” position
• Someone may have turned it off accidentally during maintenance or cleaning

Vents and Registers

Your system can’t heat or cool properly if air can’t flow freely through your home.

• Walk through every room and check that all vents are open
• Move furniture, rugs, or curtains that might be blocking vents
• Make sure return vents (the larger grilles that pull air in) are also clear
• Close vents only slightly if you need to balance temperatures between rooms. Never close them completely

Troubleshooting Common Issues

If the preliminary checks didn’t fix your problem, find your specific issue below.

No Airflow from Vents

When your system runs but you feel little or no air coming from the vents:

• Check the air filter again. Even a moderately dirty filter can reduce airflow dramatically
• Look at all return grilles to make sure they’re not blocked or covered
• Listen near the indoor unit. You should hear the blower fan running
• If the blower isn’t running but the system is on, the fan motor may have failed or overheated (turn off the system and call a technician)

System Running But No Cold Air

Your AC turns on but the air isn’t getting cold:

• Go outside and look at your condenser unit (the big box with a fan)
• Clear away any leaves, grass clippings, or debris within 2 feet of the unit
• If the coils look dirty or clogged with debris, gently rinse them with a garden hose
• Check your thermostat. Make sure it’s set to “COOL” and not just “FAN” (fan-only mode blows air without cooling it)
• Verify the outdoor unit’s fan is spinning when the system runs

System Running But No Warm Air

Your heater turns on but the air stays cold:

For gas furnaces:

• Check if the pilot light is lit (older models) or if the ignition system is working
• Look for a blinking light on the furnace control board. This light blinks error codes that help identify problems
• Make sure the gas supply valve is open (the handle should run parallel to the gas line)

For heat pumps:

• Your heat pump may be in defrost mode. This is normal and temporary
• During defrost, the outdoor unit melts ice buildup and may blow cool air for 5-10 minutes
• If defrost mode lasts longer than 15 minutes or happens constantly, there may be a problem with the defrost controls

Strange Noises

Different sounds point to different problems:

Rattling or vibrating:

• Loose screws, panels, or covers on the unit
• Turn off the system and tighten any visible loose parts
• Check if something fell into the unit or is touching it

Squealing or screeching:

• Usually indicates a belt or motor bearing problem
• Turn off the system to prevent further damage
• This typically requires a technician to fix

Buzzing:

• Often points to an electrical issue like a failing capacitor or contactor
• Could also be a loose wire
• Turn off the system and contact a technician

Clicking (when not starting or stopping):

• Repeated clicking during operation can signal a relay problem
• Normal clicking when the system starts or stops is nothing to worry about

Water Leaking

Water around your indoor unit usually means a drainage problem:

Check the condensate drain line:

• Find the drain line (usually a PVC pipe near the indoor unit)
• Pour a cup of white vinegar or bleach into the drain access point to clear minor clogs
• Use a wet/dry vacuum on the end of the drain line outside to pull out blockages

Check the drain pan:

• The pan under your unit catches condensation
• If it’s overflowing, the drain line is likely clogged
• A cracked pan needs to be replaced

For heat pumps in winter:

• Some water around the outdoor unit during defrost cycles is normal
• Large amounts of ice on the unit may indicate a refrigerant or airflow problem

When to Call a Professional

Some problems are beyond DIY fixes and require trained technicians. Call a professional immediately if you notice:

Burning Smell

A burning smell from your vents or unit is serious:

• Turn off your system immediately at the thermostat
• If the smell is strong or you see smoke, leave the house and call 911
• A burning electrical smell may indicate overheating wires or a failing motor
• Never ignore this. It can be a fire hazard

Circuit Breaker Trips Repeatedly

If the breaker trips again right after you reset it:

• Stop resetting it. Repeated tripping signals a serious electrical problem
• Continuing to reset a tripping breaker can cause electrical fires
• This could indicate a short circuit, ground fault, or oversized draw from a failing component

Refrigerant Leak

Signs of a refrigerant leak include:

• Ice buildup on the refrigerant lines or evaporator coil
• Oily residue around fittings or connections
• Hissing sound coming from the unit
• System blowing warm air when set to cool
• Higher than normal electric bills with reduced cooling

Refrigerant is harmful to the environment and handling it requires EPA certification. Only licensed technicians can legally repair refrigerant leaks.

Loud Banging or Metal-on-Metal Sounds

If your furnace makes loud banging, clanking, or metal grinding sounds:

• Turn off the system right away
• These sounds can indicate a cracked heat exchanger, loose blower wheel, or broken internal components
• Running the system with these problems can cause further damage or safety hazards

Gas Smell

If you smell natural gas (rotten egg odor) near your furnace:

• Do not turn on any lights or electronics
• Leave your home immediately
• Call your gas company’s emergency line from outside
• Do not return until the gas company says it’s safe

Keeping Your System Running Smoothly

Prevent most problems with basic maintenance:

• Change your air filter regularly (every 1-3 months, more often with pets)
• Keep the area around your outdoor unit clear of plants and debris
• Schedule professional maintenance twice a year: once before summer, once before winter
• Keep vents open and unobstructed throughout your home
• Consider upgrading to a smart thermostat for better temperature control and energy savings

If you’ve worked through this guide and still have problems, our team at AmeriTech is ready to help. We service the Central Florida area with fast, reliable HVAC repairs.