Why Does My Heater Come on When System Is Set to Cool?

Why Does My Heater Come on When System Is Set to Cool?

HVAC settings aren’t supposed to produce surprises. When you turn on the air conditioner, you have a right to expect cool air to begin flowing out of the vents. If what you get instead feels like something other than that, it’s a problem. When the HVAC settings say “Cool” but the house feels uncomfortably warm like the heater’s on, here are some possible reasons why:

Temperature setting has been changed.

If someone has increased the programmed temperature setting at the thermostat without your knowledge, the cooling function may not activate—even though the system is set to the “Cool” mode. The fan will recirculate room temperature air, which may feel warm. Check programmed temperature settings to make sure they’re still in the cool comfort range.

Clogged air filter.

Airflow through the HVAC system must meet a certain minimum volume for the cooling process to function. If the air filter is dirty and clogged, the evaporator coil cannot extract sufficient heat and the system will produce warm airflow. Check the air filter. If it appears dirty replace it now and see if cooling improves.

Compressor not responding.

The indoor HVAC blower fan and the outdoor A/C compressor unit are typically on separate electrical circuits. If the circuit breaker controlling the outdoor unit trips for some reason, the blower fan will still actuate. Since the compressor isn’t receiving power, however, the cooling process will not function and warm/hot air will flow from room vents. This scenario requires professional HVAC service to diagnose and repair.

Low refrigerant.

Circulating refrigerant extracts indoor heat at the A/C evaporator coil and conveys it to the outdoor condenser unit to be released. If the refrigerant level falls below specifications, heat extraction will not occur and the system will blow hot air. Low refrigerant is usually caused by a leak in the system. This requires a qualified service technician to pinpoint and repair the leak, then restore the refrigerant level.

If your HVAC settings aren’t delivering cool comfort, contact Aggressive Mechanical for qualified professional service.

Our goal is to help educate our customers in Monmouth County, New Jersey and surrounding areas about energy and home comfort issues (specific to HVAC systems). 

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