Why is heat coming out instead of AC?

Author: Dr. Moshe O'Kon PhD  |  Last update: Wednesday, October 8, 2025

Wrong Thermostat Setting This problem is a simple one, and you'd be surprised how often it's the culprit. Check your thermostat. Is it set to “Warm” or “Heat” instead of cooling? If so, that could be the only problem.

Why is my AC blowing heat instead of cool?

Common Causes of an Air Conditioner Blowing Warm or Hot Air

There are a number of reasons that your air conditioner isn't functioning properly and not blowing cold air. These can be due to clogging issues, electrical problems, low refrigerant, evaporator coil malfunctions, or compressor problems.

How to fix AC that's blowing warm air?

If your AC is blowing warm air, start by checking the thermostat settings to ensure it's set to ``cool'' mode. Next, inspect the air filter for clogs and replace if necessary. Check the outdoor unit for debris blocking airflow and clean it if needed. Ensure all vents are open and unobstructed.

Why does my thermostat turn on heat instead of AC?

MOST LIKELY - you have a short in your low voltage wiring causing both to come on. Often rodents can get to low voltage wiring between thermostat and air handler, and when they gnaw on wiring, various shorts occur.

Why is heat not working but AC is?

Leak in your ductwork is preventing adequate heating throughout the home. Thermostat is malfunctioning. Air filters are dirty and clogged. Furnace's blower motor needs repair.

How to Fix a Car with No Heat (Easy)

Why is my house hot but the AC is blowing?

You may have insufficient insulation and air leaks, your thermostat might need recalibrating, or you might need a new filter.

How do I know if my thermostat is bad?

7 Ways to Tell Your Thermostat Is Broken
  1. The Thermostat Has No Power. ...
  2. The AC or Furnace Won't Turn On. ...
  3. The Heater or AC Won't Turn Off. ...
  4. The Thermostat Reading Doesn't Match the Room Temperature. ...
  5. The Thermostat Doesn't Respond. ...
  6. The HVAC System Is Short Cycling. ...
  7. The Thermostat Forgets Programmed Settings.

Why is my AC running in heat mode?

There are a few reasons why this might happen: it may be an easily-fixed mix-up in your thermostat's HVAC settings, the need for some basic maintenance, or a potentially-serious electrical problem.

Why does my thermostat kick on but no AC?

Issues with Electrical Wiring

Electrical wiring issues can often be a culprit when your thermostat clicks but your AC system fails to initiate. If there is a loose connection somewhere in the wiring, the thermostat may send a signal to the control board, but the command might not reach the AC system.

Will a bad thermostat cause no heat?

Often, no heat in the home is a result of thermostat issues, whether they be true malfunctions or errors in settings. Whenever you notice no heat, check your thermostat first for troubleshooting. Make sure your thermostat is on – the display should be on as normal. If it's not, there could be a power issue.

Why is warm air coming out of AC vents?

The Two Most Common Causes of Home AC Blowing Hot Air

If you're getting hot air, it usually means one of two things: There's a problem with the compressor or the outside unit, or. Your AC is low on refrigerant.

Why is my AC struggling to cool?

Proper airflow is crucial for an AC system to cool your home efficiently. Several factors can compromise airflow, including blocked or obstructed vents, closed or incorrectly adjusted dampers, and dirty or obstructed evaporator coils. These issues restrict the air's flow, reducing the system's cooling capacity.

Should I turn off the AC if it is blowing warm air?

One of the solutions to HVAC blowing hot air would be to turn off your unit, clean the condensation drain, and allow the coils to defrost before turning the system back on.

How to fix AC blowing out warm air?

If your AC is blowing warm air, start by checking the thermostat settings to ensure it's set to "cool" mode. Next, inspect the air filter for clogs and replace if necessary. Check the outdoor unit for debris blocking airflow and clean it if needed. Ensure all vents are open and unobstructed.

How to reset a thermostat?

Most modern thermostats will have a clearly marked reset button inside the panel. It's usually small and recessed, so you might need a pointed object like a paperclip to press it. For those wondering specifically how to reset air conditioner thermostat models, the process is generally the same.

Why is my AC running but not blowing cold air?

If your AC is running but not cooling, it could be due to a dirty air filter, incorrect thermostat settings, a malfunctioning thermostat, a refrigerant leak, dirty condenser coils, blocked vents or ducts, a faulty compressor, frozen evaporator coils, or electrical issues.

Why is my thermostat not blowing the AC?

If your thermostat is not working, you may want to check your AC filters. The filters are responsible for trapping dirt and dust particles. If the filters are not working, the thermostat will not be able to function correctly. When the air filters are dirty and clogged, air will struggle to pass through them.

How to reset an AC unit?

Press the reset button. Most models require you to hold the button down for 3-5 seconds before releasing. Restore power to your AC. Restore power to the unit at the circuit breaker, and make sure the unit is set to “on” and your thermostat is set to “cool.”

What fuse controls the AC and heat?

Typically, AC systems use “TR”-type fuses to ensure safe system operation. However, if you're in a pinch and need to replace a fuse quickly, you can use a fuse that is rated for a lower amperage than what the system is rated.

Why is my heat coming on instead of AC?

In many cases, something as basic as replacing expired thermostat batteries, tightening loose sensor wires, or upgrading failing circuit board components restores immediate comfort control and coordinated equipment functionality, avoiding improper heating events coinciding with air conditioning mode attempts.

Why is my AC only coming out hot?

Most likely guess is that you have low (or zero) refrigerant - which means that either it's very old and due for a service - or it has a leak. There are other possible reasons (bad thermostat, broken hose, blocked air inlets, bad compressor) - but refrigerant leak is the most likely.

Should the outside fan run when AC is on?

The short answer: Definitely not. (Unless you have manually engaged your outside fan to run constantly, but it shouldn't be running for hours on it's own.) If your HVAC is functioning correctly, it should keep your house cool by cycling on for 15-20 minutes at a time—with distinct pauses in between each cycle.

Why is my HVAC not responding to the thermostat?

Try checking the circuit breaker box or replacing the batteries. Bad wiring: The thermostat may be unresponsive if the wiring has gone bad. Remove the cover and check inside for loose, detached, or corroded wires. If you spot any problems, contact an HVAC technician for assistance.

How can I tell if I need to replace my thermostat?

Signs You Need a New Thermostat
  1. Heating or cooling system will not turn off or on.
  2. The temperature reading is incorrect.
  3. Recent spike in your energy bill.
  4. Frequent temperature fluctuations.
  5. Thermostat is 10 years old or older.

Is my AC broken or is it just hot?

You should feel cold, or at least cool air, coming out of your air vents. If there is warm air or no air at all, your air conditioning unit may have a problem. Be sure to do a visual inspection of your vents as well. You may have holes or tears, or ductwork that has come disconnected.

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