AC Isn’t Blowing Hot Air? | Troubleshooting Tips from Dezier Air

If your AC isn’t blowing hot air during the winter, you’re not alone; this is one of the most common service calls we receive. There are several reasons this can happen, but the good news is that most of them can be prevented with proper maintenance.

Common Causes Your AC Isn’t Blowing Hot Air in Winter

1. Lack of Maintenance: Keep Your HVAC System Running Efficiently

Whether you have a ductless mini-split, ceiling cassette, ducted system, or air handler, every type of HVAC unit needs routine maintenance to operate efficiently. Dirty filters, coils, or drain pans can restrict airflow, reduce performance, and even cause system failure.

The filter is your system’s first line of defense. Running your system with a dirty filter for too long can lead to costly repairs—or worse, a full replacement. Many modern units display error codes when it’s time to clean or replace filters, so don’t ignore those alerts.

If the filter is completely obstructed, it can cause the coils within the system to clog. When a coil is clogged, it cannot adequately send refrigerant throughout the system, causing the coils to freeze over and further restrict proper operation. Once the system is turned off, the coils defrost and water begins to leak from the drain pan because excess condensation has accumulated from the frozen coils.

Most manufacturer manuals recommend cleaning washable filters once a week. If you think you’re cleaning yours often enough, you might want to double-check. Consistent maintenance is key to preventing heating issues.

For a full guide, see our Essential Guide for Maintaining HVAC Coils, Drain Lines & Air Filters. You can also check out Why Coil Cleaning in Window AC Units Is More Than Just a Quick Wipe for expert tips on coil care.

2. Refrigerant Leaks: Why Your AC May Not Heat Properly

Another common cause of your AC not heating is a refrigerant leak. These leaks can be tricky to spot since they’re often caused by small pinholes, damaged fittings, or kinked pipes. A refrigerant leak reduces your system’s ability to heat (or cool) effectively and can lead to bigger problems over time.

Technicians may refer to a system being “low on charge,” which means it doesn’t have enough refrigerant to function properly and needs to be recharged. The amount of refrigerant required depends on both the factory charge your system calls for and any additional charge needed to satisfy the run from the condenser to the indoor unit(s).

Refrigerant leaks can lead to costly repairs if left unchecked. With a maintenance plan, technicians can monitor the system’s functionality and identify any early signs of a leak before it becomes serious.

If you suspect a refrigerant leak, it’s best to schedule a professional inspection to prevent further damage and higher repair costs.

3. Faulty Control Boards: When Your AC Needs Professional Repair

Your HVAC system’s control boards act as the “brain” of the unit. When a board fails, the system can’t communicate properly, resulting in heating or cooling issues. Like most components, control boards wear out over time and may need replacement.

A professional technician can test and replace faulty boards to restore your system’s performance. Learn more about our professional HVAC services for quick, reliable repairs.

4. Heater Not Blowing Warm Air Because of Thermostat Settings

Your HVAC system operates via the thermostat, so incorrect settings are a common source of heating issues.

If you have a heat pump system that isn’t blowing warm air, make sure all indoor units connected to the same condenser are set to the same mode—either “heat” or “auto.” The system won’t function properly if some units are calling for cooling while others are calling for heating.

If your thermostat is set to heating and your system is still not producing warm air, it’s time to give us a call.

5. Improper or Insufficient Insulation Leading to Heating Issues

If your home isn’t properly insulated, it can allow heat to escape and cold air to enter, compromising the efficiency of your heating system. Poor insulation forces your system to work harder to heat your space, which can increase wear and energy costs.

When to Call an HVAC Professional for AC Troubleshooting

Troubleshooting your AC system can be complex, and “no heat” calls are especially critical during the winter. The issues listed above are only a few possible causes; there are many others that require professional attention.

If your air conditioner isn’t blowing hot air, don’t wait for the temperatures to drop further. Contact us today to schedule a diagnosis and get your system back to peak performance. Sometimes the issue isn’t just a repair; it’s that your unit has reached the end of its lifespan. Learn more about how long HVAC systems should last in our HVAC Installation Cost & Lifespan Explained guide.