Why Is Your AC Blowing Warm Air in Your San Jose Home?

When temperatures in San Jose reach the 80s—and even higher during summer heatwaves—your home’s air conditioner should be your refuge from the heat. So, if your AC begins blowing warm air instead of cooling your home, it’s disruptive, uncomfortable, and may be costly.

This common problem can be caused by something as simple as a misconfigured thermostat or something more serious, such as a refrigerant leak or a failing compressor. Regardless of the cause, it indicates that your system isn’t working correctly and requires attention.

In this blog, we’ll explore common reasons your AC might blow warm air, outline what you can troubleshoot yourself, and explain when to contact an HVAC professional.

If your cooling system isn’t working effectively, IRBIS Air, Plumbing & Electrical can help. We’re a trusted HVAC team, ready to restore your comfort quickly and efficiently. Call us at (669) 322-8182 or request a service online.

Quick Checks First: Simple Troubleshooting You Can Do

Before you pick up the phone, it’s worth checking a few simple things that could be behind the warm air problem. These quick troubleshooting tips can help restore your AC’s performance without needing a service call.

The following are steps you can take on your own:

• Check your thermostat settings – Make sure the system is set to “Cool” and the fan is set to “Auto.” Sometimes, the fan may be running without the compressor if it’s set to “On” or the mode is accidentally changed.
• Inspect and replace dirty air filters– A clogged filter restricts airflow, causing your system to overheat or freeze, which can result in warm air blowing through the vents. Check your filter monthly and replace it every 1–3 months for optimal performance.
• Check for blocked vents or return air grilles – Furniture, rugs, or curtains can obstruct airflow. Clear blockages around your supply vents and return grilles to allow air to circulate freely.
• Reset the circuit breaker – If the outdoor condenser unit loses power due to a tripped breaker, the AC may still blow air, but it won’t be cooled. Check your electrical panel, locate the AC breaker, and reset it. If it trips again immediately, do not reset it multiple times—this indicates a deeper electrical issue.

A mechanical or system-level fault is probably the cause if these simple checks don’t fix the problem.

Serious AC Problems That Require Professional Repair

When basic troubleshooting doesn’t resolve the issue, your AC might be experiencing more serious internal problems. These typically require licensed HVAC technicians with the proper tools, training, and certifications to perform repairs safely and effectively.

Common mechanical problems that can lead to warm air include the following:

• Low refrigerant levels or a leak – Refrigerant is essential to cooling. If your system is low on refrigerant—often due to a leak—it can’t absorb and release heat efficiently. This is not a DIY repair. Refrigerant leaks must be located and repaired by EPA-certified technicians who can recharge the system to proper levels. Handling refrigerant without certification is illegal and dangerous.
• Dirty condenser coils – The outdoor condenser releases heat from your home. When the coils are covered in dirt, leaves, or grime, they can’t dissipate heat efficiently, causing the system to blow warm air. Cleaning condenser coils properly requires specific tools and chemicals. Incorrect cleaning can damage the delicate fins and reduce efficiency even further.
• Frozen evaporator coil – A frozen indoor coil is often caused by restricted airflow or low refrigerant. As the coil ices over, it can no longer absorb heat, leading to warm, humid air circulating through your home. The ice must be thawed fully, and the root cause diagnosed and fixed to prevent recurring issues.
• Faulty compressor – The compressor is the core of the AC system. It pressurizes refrigerant to help move it through the system. If the compressor fails, cooling stops altogether. Compressors are expensive to repair and may indicate it’s time to evaluate whether replacing your unit is more cost-effective, especially if your system is older.
• Electrical issues (capacitors, wiring, relays) – Faulty capacitors, loose or damaged wires, or failed contactors can prevent critical components like fans or compressors from starting. Electrical problems pose serious safety risks and should be handled by a professional.

If you suspect any of these problems, act quickly. Continued operation of a malfunctioning AC unit can lead to further damage and higher repair costs.

When It’s Time to Call an HVAC Professional

A fine line exists between simple maintenance and problems that require professional help. If your AC keeps blowing warm air after you’ve done the basic checks, it's time to call a technician.

Consider calling an HVAC professional if:

• Troubleshooting doesn’t work – You've checked the thermostat, replaced the filter, and cleared vents, but the warm air persists.
• Signs indicate a refrigerant leak – Hissing sounds, ice buildup, or noticeably reduced cooling are red flags.
• Strange noises or smell odd odors come from the unit – Grinding, buzzing, burning smells, or musty odors could point to electrical problems or mold growth.
• No power is going to the unit after resetting the breaker – This could signal a deeper electrical fault that requires professional diagnosis.
• The system is old or frequently breaking down – If your AC is 10–15 years old and frequently fails, it might be time for an evaluation to determine whether repair or replacement is more sensible.

How to Prevent Warm Air Issues in the Future

Consistent, preventative maintenance is an effective way to avoid the hassle of your AC blowing warm air.

Steps you can take include:

• Scheduling regular professional tune-ups – Annual inspections and maintenance—ideally in early spring—can keep your system in peak condition ahead of the summer heat. Technicians check refrigerant levels, clean components, inspect electrical systems, and make sure your AC is ready to perform.
• Keeping up with DIY maintenance – Simple habits like changing filters regularly and keeping the outdoor unit clear of debris can make a big difference in system performance.
• Staying proactive about system health – Preventative care protects your comfort, helps reduce energy bills, prevents major repairs, and extends the life of your AC system.

Restore Your Comfort with Help from Professionals

Your air conditioner blowing warm air is a sign that something needs attention. Whether the fix is a quick filter change or a more serious repair, understanding the cause is the first step to making your home cool and comfortable again.

For professional, prompt, and trusted AC solutions in San Jose, turn to our team at IRBIS Air, Plumbing & Electrical. Call us at (669) 322-8182 or complete our online contact form to schedule an AC repair or diagnostic service.