The hot summer sun in Fullerton, CA, is enough to make you want to escape to a cool oasis. With a properly running air conditioning system, you can find this oasis inside your home. However, if your air conditioner blows warm air instead of cold, you're not going to find relief from the outdoor heat. There are several reasons your air conditioner could be blowing warm air. Read on to learn more about the most common causes, then reach out to One Hour Heating & Air Conditioning® in Fullerton for emergency HVAC services so we can restore your home’s comfort.

Thermostat Settings

When you feel warm or hot air coming from the vents, first check your thermostat. Make sure it’s set to “Cool,” and that the temperature is lower than the current indoor temperature. Also, check the fan setting. If it’s switched to “On,” it will run constantly, even when your AC isn't actively cooling. This can cause the air coming from the vents to feel warm. Even if the settings are correct, your thermostat could still be the issue. A malfunctioning thermostat may send incorrect signals to your AC system. Our team can help troubleshoot, repair, or replace your thermostat as needed.

Dirty Air Filter

Your AC’s air filter traps dust and debris from the air before it circulates through your system. When that filter is clogged, airflow is restricted. This prevents enough air from moving across the evaporator coil, meaning the system struggles to cool the air before it reaches your vents. A dirty filter also puts unnecessary stress on your system and can contribute to freezing coils or poor performance. Change your filter every 1 to 3 months, depending on your home’s environment. If you feel warm air from the vents, checking the filter is one of the first things you can do yourself.

Dirty Coils

Dust and debris can also accumulate on your evaporator or condenser coils. This buildup insulates the coil and limits heat transfer, which means your AC can't adequately cool the air. In some cases, dirty coils can even cause the system to freeze over. We include a thorough coil cleaning as part of our annual AC maintenance service. Scheduling maintenance in the spring helps ensure your system runs efficiently all summer long.

Refrigerant Loss

Refrigerant absorbs heat from your home and releases it outside. It circulates in a closed loop and doesn’t get used up. So if your AC has low refrigerant, it usually means there’s a leak. In addition to warm air, signs of a refrigerant leak may include ice buildup on the coils or a faint hissing noise. A licensed HVAC technician must repair leaks, as refrigerants can be harmful to the environment and require proper handling.

Faulty Compressor

The compressor is the heart of your AC system; it pumps refrigerant through the coils and keeps the cooling cycle running. If the compressor fails or malfunctions, your system may blow warm air or stop working entirely. We provide fast, same-day repair service for compressor issues and always use high-quality parts to get your system back up and running.

Frozen Coils

Frozen evaporator coils can block airflow, leading to little or no air coming from your vents, or even warm air. Causes of frozen coils include dirty filters, dirty coils, low refrigerant, or airflow restrictions. While low outdoor temperatures can also cause coils to freeze in some climates, that’s less common during a Fullerton summer. If your coils are frozen, shut off the system and let it thaw completely. If it refreezes after restarting, call us right away to prevent further damage.

Ductwork Issues

Leaky or blocked ducts can prevent cool air from reaching your vents. Holes or gaps in the ducts may allow cooled air to escape into unconditioned spaces, while clogs can limit airflow altogether. We recommend having your ductwork inspected every 3 to 5 years and cleaned as needed, especially after major renovations or if you’ve noticed increased dust or uneven cooling. We’ll also check for signs of leaks, disconnected ducts, or crushed sections that could be affecting performance.

Old and Tired System

If your AC system is more than 10 to 15 years old and blowing warm air, it may be nearing the end of its life. Over time, systems lose efficiency and may struggle to keep up, even if they’re still technically running. If you’ve noticed frequent breakdowns, rising energy bills, or inconsistent comfort, a replacement may be the smarter option. We’ll help you find a new system that fits your home and budget: one that delivers strong, consistent cooling.

Schedule Service With Our Experts Today

Reliable and efficient air conditioning is essential for summer in Fullerton. If your system isn’t keeping you cool, call One Hour Heating & Air Conditioning® for fast, expert repair. We offer AC repair, installation, ductwork inspections, maintenance plans, and indoor air quality services. Our licensed technicians are here to help restore your comfort, no matter the issue. Call One Hour Heating & Air Conditioning® in Fullerton today and let us bring cold air back into your home.