How Do You Troubleshoot an AC Unit Not Cooling?

Van Bremen's Heat & Air
Dec 17, 2025
4 min read

AI Summary

When an AC unit stops cooling, the most common causes include dirty filters, blocked airflow, refrigerant issues, thermostat problems, and electrical faults.
Troubleshooting should start with simple homeowner checks before moving to professional diagnostics to avoid damage or safety hazards.
Homes in Pennsylvania and West Virginia often experience cooling failures due to humidity, clogged coils, aging equipment, or lack of maintenance.
Van Bremen’s Heat & Air provides expert heating, cooling, and maintenance services to diagnose AC failures and restore comfort quickly.

Understanding HVAC Warranties: What Homeowners in WV & PA Should Know

A warm home in the middle of summer is more than uncomfortable; it can also signal deeper issues with your air conditioning system. When your AC stops cooling, several hidden problems may be affecting airflow, refrigerant levels, electrical components, or thermostat settings. Homes across Pennsylvania and West Virginia experience cooling issues often due to humidity, seasonal temperature swings, and aging HVAC systems.

This long-form guide walks you through how to troubleshoot an AC unit that isn’t cooling, what each warning sign means, and when to call a professional.

The Problem: AC Cooling Failure Can Have Many Hidden Causes

An AC unit that runs but does not cool often indicates underlying problems such as:

Blocked airflow
Thermostat malfunctions
Frozen coils
Low refrigerant
Dirty filters
Electrical failures
Clogged condensation drains
Outdoor unit issues

Ignoring these issues can lead to system breakdowns, high energy bills, and more expensive repairs.

The Solution: Follow a Step-by-Step Troubleshooting Process

Below are the most effective troubleshooting steps to restore cooling or identify what needs professional repair.

Step 1: Check and Replace the Air Filter

The easiest and most common fix

A dirty or clogged filter restricts airflow, causing:

Weak cooling
Frozen evaporator coils
Overheating
Longer run times

Replace the filter if it appears dusty, gray, or clogged. Most homes need a replacement every one to three months.

Step 2: Verify Thermostat Settings

Incorrect thermostat settings can mimic AC failure.

Check that:

It is set to COOL, not FAN or HEAT
The temperature is set lower than the room temperature
The thermostat display is working properly
Batteries are not dead (if battery-powered)

If the thermostat is unresponsive, it may need repair or replacement.

Step 3: Inspect the Outdoor Unit

The outdoor condenser must stay clean and clear for proper cooling.

Look for:

Grass, weeds, or debris blocking airflow
Dirt or leaves on the condenser coil
Ice on refrigerant lines
Damaged fins

Clear debris gently and keep at least two feet of space around the unit.

Step 4: Check for Frozen Evaporator Coils

Frozen coils are a major cause of cooling failure.

Signs include:

Ice on the indoor unit
Ice on refrigerant lines
Reduced airflow
Warm air blowing from vents

Turn the AC off and run the fan to thaw the coil. Frozen coils usually point to:

Dirty filters
Low refrigerant
Restricted airflow
Blower motor issues

You may need a technician to identify the root cause.

Step 5: Inspect Vent and Duct Blockages

Closed or blocked vents prevent air from spreading through your home.

Check for:

Furniture covering vents
Rugs blocking floor registers
Dust buildup inside grills

Poor duct design, leaks, or blockages may also reduce cooling.

Step 6: Check the Circuit Breaker

Cooling issues may stem from:

A tripped breaker
Blown fuse
Electrical surge

Reset the breaker if tripped. If it continues to trip, call a professional immediately.

Step 7: Listen for Unusual Noises

Strange sounds often tell you what’s wrong:

Hissing: refrigerant leak
Grinding: motor failure
Clicking: electrical problem
Buzzing: failing capacitor

Unusual noises mean the AC needs professional attention.

Step 8: Look for Signs of Low Refrigerant

Low refrigerant prevents your AC from cooling.

Symptoms include:

Warm air blowing
Long cooling times
Ice on the coils
Hissing or bubbling sounds

Refrigerant is not a DIY fix. A licensed technician must repair leaks and recharge the system.

Step 9: Check the Condensate Drain

A clogged drain can shut down the AC to prevent water damage.

Signs of clogging:

Water around the indoor unit
Musty smells
System shutting off unexpectedly

A technician can clear the line and ensure the safety switch operates correctly.

Step 10: Evaluate the System Age

Most AC units last 10 to 15 years. Older units lose efficiency and break more often.

Replacement may be more cost-effective if your system:

Uses outdated refrigerant
Requires frequent repairs
Struggles to keep up with the summer heat

A professional evaluation helps determine the best solution.

FAQ Section

Q: Should I turn off my AC if it’s not cooling?

A: Yes. Running a malfunctioning system can cause further damage, especially if the coils are frozen.

Q: Can I fix low refrigerant myself?

A: No. Refrigerant handling requires certified technicians and proper leak detection tools.

Q: Why does my AC blow warm air?

A: Blocked coils, low refrigerant, thermostat issues, or a failing compressor may be the cause.

Q: How often should my AC be serviced?

A: At least once a year to ensure performance and catch problems early.

Restore Comfort Quickly With Professional AC Repair

When your AC stops cooling, it’s important to troubleshoot early and call for help before small issues turn into major breakdowns. Whether the problem is airflow, refrigerant, electrical components, or thermostat settings, addressing it quickly restores comfort and protects your system.

Van Bremen’s Heat & Air proudly serves Pennsylvania, West Virginia, and nearby regions with expert heating, cooling, and maintenance services to diagnose failures and get your AC running efficiently again.