Why is My Commercial HVAC System Blowing Warm Air?

There is nothing worse than walking into your retail store, office building, or restaurant on a 95-degree July afternoon only to discover that the AC vents are blowing 80-degree air.

When a commercial HVAC Rooftop Unit (RTU) stops cooling, the comfort of your employees and the patience of your customers drop rapidly. If your system is blowing warm air, here are the top 4 mechanical failures happening on your roof right now.

1. Severely Dirty Condenser Coils

This is the number one cause of warm air complaints in the commercial HVAC industry. The condenser coil (located on the outside of the RTU) is responsible for taking the heat removed from your building and rejecting it into the outside air. If the condenser coil is choked with cottonwood seeds, dust, and street grime, the system cannot “breathe.” The heat remains trapped inside the refrigerant loop. The compressor will overheat, the high-pressure safety switch will trip, and the unit will only blow unconditioned, warm air.

• The Fix: A professional chemical coil cleaning immediately restores heat transfer and cooling capacity.

2. Low Refrigerant (The Micro-Leak)

An HVAC system is a closed loop. It does not “consume” or “burn” Freon. If the system is low on refrigerant, there is a physical leak in the copper tubing, usually in the evaporator coil. When the refrigerant level drops, the system loses its ability to absorb heat. You will notice the air coming out of the vents getting progressively warmer over a few weeks.

• The Fix: Simply “topping off” the unit is illegal and unethical. A certified technician must locate the leak using an electronic sniffer, braze the hole, and recharge the system to factory specifications.

3. The Failed Compressor

The compressor is the engine of the RTU. If the compressor has suffered a mechanical failure (broken valves) or an electrical failure (burned windings), the RTU is effectively dead. The blower motor will still push air through the ductwork, but because the compressor isn’t circulating the refrigerant, the air will be room temperature.

• The Fix: A compressor failure requires a massive repair or a complete RTU replacement.

4. Broken Economizer Dampers

Commercial RTUs feature an “economizer”—a set of mechanical dampers that open to let in cool outside air when the outdoor temperature is favorable (called “free cooling”). However, the actuators that control these dampers frequently break. If the damper breaks in the 100% OPEN position during a 95-degree summer day, your RTU will constantly suck 95-degree air directly into the building, overwhelming the AC.

• The Fix: A technician must access the roof, disconnect the broken actuator, manually shut the dampers, and order an OEM replacement part.

Stop the Guessing Game

If your building is hot, do not wait for the compressor to burn out. Contact HP Mechanical for Priority HVAC Dispatch. Our technicians will arrive with fully stocked vans, ready to clean coils, repair leaks, and restore cold air to your facility immediately.