Cool air blowing throughout your home provides a refuge from hot summer days. When you find the air conditioner blowing warm air, your frustration levels are likely to rise alongside the heat within your house! As frustrating as it may be, air conditioning, or AC, blowing hot air is actually a pretty common problem. Many causes may be resolved with some DIY troubleshooting of your air conditioning unit.
As a local Grand Rapids business, the technicians at A-1 Mechanical aim to protect the safety of our neighbors. Before you experience an issue within your AC unit know the most common causes, what to do to fix it, and when to call in our expert air conditioner repair pros for solutions. This may keep your AC unit blowing cold air without interruption.
Why Is My Air Conditioner Blowing Hot Air?
Your air conditioner may blow hot air when something blocks cooling or airflow through the system. Before scheduling air conditioning repair, check the most common causes:
- The thermostat is set to HEAT instead of COOL
- The fan is set to ON instead of AUTO
- The air filter is dirty or clogged
- The outdoor unit is blocked by dirt or debris
- The evaporator or condenser coils are dirty or frozen
- The thermostat is old, locked, or not responding correctly
If these steps do not restore cool air, a professional can diagnose the central air system and make the right repair.
Why Your Air Conditioner Is Blowing Warm Air
If you have an air conditioner blowing hot air during the summer months, here are the most common causes and what you can do to correct them or when you should call for AC repair services.
Incorrect Thermostat Settings
In larger households, it’s easy for thermostat settings to be adjusted without the knowledge of other family members. If someone accidentally turns the thermostat to HEAT mode, it won’t be your air conditioning system generating hot air – it’s actually your furnace running, heating the home! If vents are blowing warm air check your thermostat first.
Another issue with thermostat settings that can send hot air into the home is a fan set to ON mode instead of AUTO. When the AUTO setting is selected, your HVAC system’s fan only runs with a cooling cycle to circulate chilled air into living spaces across the house. When ON mode is selected, the fan will run all the time. In between cooling cycles, the fan pushes warm air through the vents, because air is not actively being cooled.
Some thermostats feature a lock setting. This feature prevents switching between modes and adjusting the temperature settings. Since many homeowners only interact with the thermostat occasionally, it is easy to think you changed modes even though the thermostat was locked. In these cases, the issue is simple to resolve.
Whenever you have an AC system that’s blowing hot air, it’s wise to check the thermostat settings first.
- Make sure the thermostat switch is set to COOL mode, not HEAT or HEAT/COOL.
- Check the fan settings switch and make sure it is set to AUTO mode, and not ON.
- On smart thermostats you should verify that the app is working by adjusting settings directly on the display.
As they age, thermostats can become faulty. Components may corrode and fail due to time, power surges and other factors. If the display is not working properly or if the thermostat is over 10 years old, our team can install a new thermostat and improve the efficiency of your system.
Dirty Air Filter
A dirty air filter can cause your air conditioner to blow hot air out of the vents. When contaminants build up, a blockage may be created. Clogged air filters force your cooling system to work harder, starving the system of the air needed to circulate smoothly. Your air handler may not be able to generate enough airflow, leaving the air feeling warm as it exits your vents. All the while, clogged air filters will be wasting electricity as the air handler attempts to compensate for the restricted filter.
When your AC is blowing hot air, check your HVAC filter and replace it as needed. It’s wise to check air filters once per month in the summer, as replacement may be needed more often during this season of increased system usage.
- Remove the old filter from the filter cabinet.
- Look at the filter’s surface – if it is completely caked in grayish material, it needs to be replaced. If you are unsure, hold the filter up to a light and see if you notice any light shining through. If no light passes through the filter, replace it. The basic rule is to replace dirty filters once every month during the hottest and coldest months.
- Insert a new filter into the filter cabinet. Make sure to follow the airflow arrows on its frame which tell you the proper direction for filter installation. Make sure the filter is the correct size and fits snugly into the cabinet.
Dirty Outdoor Unit
Blowing warm air may also be due to blockages and clogs in the outdoor unit. A unit needs airflow to work optimally and stay cool. A dirty outdoor unit may overheat or experience unnecessary failure. During annual tune ups our technicians completely inspect and condition the AC unit. Detecting a refrigerant leak, damaged refrigerant line and especially dirty condenser coils is part of professional maintenance. If your outdoor AC unit is dirty, you should refer to the owner’s manual and most likely contact our team.
AC Coils
Frozen evaporator coils should prompt a call to our team. Your central air conditioner or heat pump uses two sets of coils – the indoor evaporator coil, and the outdoor condenser coil. If either of these coils are dirty, the system struggles to complete heat transfer, which can result in your AC blowing warm air. A dirty evaporator coil prevents it from absorbing heat within the indoor air; dirt on the condenser coil, meanwhile, prevents the system from efficiently releasing heat outdoors.
Coil cleaning is a job best left to the professionals. If you suspect your coils may be dirty, you can check by disconnecting power to the system and opening the access door to your furnace or air handler indoors to check the condition of the evaporator coils, or look inside the outdoor condenser unit or heat pump unit to check the condenser coils. If either are covered in dirt or grime, call your HVAC company to clean the coils.
Schedule AC Repair When Your Air Conditioner Blows Hot Air
If you have an AC blowing warm air and the above troubleshooting steps don’t work, call A-1 Mechanical to perform air conditioner repairs at your home. Our technicians perform diagnostics to find out why you have an air conditioner blowing hot air so the correct repairs can be made to solve the problem once and for all.
Frequently Asked Questions
Question: Why is my air conditioner blowing hot air instead of cold air?
Answer: Your air conditioner may blow hot air because of incorrect thermostat settings, a dirty air filter, a dirty outdoor unit, or dirty or frozen AC coils. A-1 Mechanical recommends checking simple settings first, then calling for professional AC repair if the system still does not cool properly.
Question: What thermostat settings should I check if my AC is blowing warm air?
Answer: Make sure your thermostat is set to COOL, not HEAT or HEAT/COOL. You should also set the fan to AUTO instead of ON. When the fan runs constantly, it can push warm air through the vents between cooling cycles, even when the air conditioner itself is not actively cooling.
Question: Can a dirty air filter make my AC blow hot air?
Answer: Yes, a dirty air filter can restrict airflow and make your air conditioner work harder than it should. When the system cannot move enough air, the air coming from your vents may feel warm. During heavy summer use, A-1 Mechanical recommends checking your filter monthly and replacing it when dirty.
Question: Should I call a professional if my AC coils are dirty or frozen?
Answer: Yes, dirty or frozen AC coils should be handled by a professional HVAC technician. Coils help transfer heat, and when they are dirty or frozen, your system may struggle to cool your home. A-1 Mechanical can inspect the system, clean the coils, and diagnose the cause.
Question: When should I schedule AC repair for warm air from my vents?
Answer: Schedule AC repair if thermostat checks, filter replacement, and basic troubleshooting do not solve the problem. A-1 Mechanical’s technicians can perform diagnostics to find the cause of hot air from your AC and make the right repairs so your system can cool reliably again.