HVAC Symptoms Index

If your heating or cooling system is acting strange, this index helps you quickly find the symptom that matches what you’re experiencing.
Choose the category below to explore clear explanations, common causes, and safety notes for each type of HVAC issue.

Heating Problems

• No heat coming from vents
• Furnace clicking but not starting
• Uneven heating throughout the home
• Cold air blowing when heat is on
• Burning smell when heat turns on

Cooling Problems

• AC running but not cooling
• Warm air coming from vents
• AC short cycling
• AC not turning on
• AC freezing up or icing over

Airflow & Vent Issues

• Weak airflow from vents
• One room hotter or colder than others
• No air coming from certain vents
• Whistling vents or airflow noise
• Blocked or restricted airflow

Noises & Vibrations

• Banging or knocking sounds
• Rattling or vibrating equipment
• Buzzing or humming noises
• High‑pitched whistling
• Metal‑on‑metal scraping

Smells & Odors

• Burning smell from vents
• Musty or moldy odors
• Sweet or chemical smells
• Electrical or metallic odors
• Rotten or unusual smells

System Performance & Energy

• System running constantly
• High energy bills
• HVAC not keeping up with temperature
• Short cycling or frequent restarting
• Poor overall performance