Common AC Issues & Causes

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If your AC is running but your home isn’t getting cool, the issue is usually one of these:

Check first:

• Thermostat set to cool and below room temp 
• Air filter (dirty filters are the #1 cause) 
• Vents open and not blocked 

Common causes:

• Low airflow (dirty filter, duct issues) 
• Dirty evaporator coil 
• Refrigerant issue (not always a leak—often misdiagnosed) 

👉 If airflow isn’t correct, adding refrigerant won’t fix the problem.

Ice on the indoor coil or refrigerant lines?

Most common causes:

• Restricted airflow 
• Dirty coil 
• Blower not moving enough air 

What to do:

• Turn system OFF 
• Let it thaw completely 
• Replace filter 

👉 Do NOT run it frozen—you can damage the compressor.

If airflow feels weak:

Possible issues:

• Dirty filter 
• Undersized or restricted ductwork 
• Blower motor or capacitor issue 

👉 This is one of the most misdiagnosed problems in HVAC.

Common causes:

• Thermostat placement issues 
• Oversized system 
• Electrical or control problems 

👉 Short cycling increases wear and drives up energy bills.

Different sounds usually point to different problems:

• Buzzing: electrical issue or capacitor 
• Grinding: motor bearings 
• Rattling: loose components 

👉 Unusual noises should be checked early before bigger damage happens.

Likely causes:

• Clogged condensate drain 
• Drain line blockage 
• Improper installation 

👉 Ignoring this can lead to water damage and mold.

Check:

• Thermostat batteries 
• Breaker panel 
• Disconnect at outdoor unit 

If all that checks out:
👉 likely electrical or control issue

After 40+ years in HVAC, we’ve found that many systems are:

• misdiagnosed 
• overcharged with refrigerant 
• or recommended for replacement unnecessarily 

Most problems come down to airflow, installation, or setup—not major equipment failure.

Call if:

• System keeps freezing 
• Airflow is still weak after filter change 
• You hear unusual noise
• Cooling is inconsistent