HVAC Keeps Blowing


When your air conditioner won’t stop running, it’s normal to be concerned about wasting electrical power as temperatures drop too low for comfort. When your HVAC unit won’t shut off and never seems to stop blowing air, the problem could be caused by several malfunctioning components. Some of these issues may involve frozen evaporator coils, a bad electrical relay switch that needs to be replaced, a clogged air filter, dirty condenser coils, a bad thermostat, or another problem with your HVAC system. 

FiveStar Plumbing, Heating and Cooling explains the top reasons your air conditioner fan keeps running and won’t shut off. A FiveStar air conditioning specialist is standing by to schedule a time to come out or will visit your home the same day for emergency heating and cooling repairs.

If your HVAC unit is constantly running and blowing out air for hours or days, then immediate attention from a qualified HVAC professional is needed. If you allow your unit to keep running, you are wasting a significant amount of electrical power, as well as wear and tear on your HVAC system. This can cause serious and costly damage, such as needing replacement parts or a whole new unit all together.

Why won’t my air conditioner turn off?

Electrical Issues:

Air conditioners have a number of electrical components. A relay switch that gets stuck allows an electrical circuit to remain closed, which means it is continuously supplying power to the HVAC unit. The compressor contactor can get fused into a closed position, allowing the condenser unit to continue to run with endless power. Sometimes a stuck switch can be repaired, but typically you will need to have a technician replace the problematic switch.

Faulty Thermostat:

Thermostats should be replaced roughly every 10 years. Over time, the thermostat sensors gather dust and debris which makes it difficult for them to accurately read the room temperature. Electrical wiring can become damaged, causing weaker connections, and communication disrupts between the thermostat and the air conditioner. 

Wrong Thermostat Settings:

It may seem that your air conditioner is constantly running even when the system is set to “Fan.” Selecting the ON fan mode on your thermostat will power the blower motor and fan to constantly run, instead of only when the cooling system cycles. You can hear the indoor components running and feel hot air blowing out of the vent, because the air conditioner isn’t set for producing cool air.

Your AC unit could also always be running because the set temperature on the thermostat is different than expected. In households with multiple people making thermostat adjustments, the set temperature may be different than what you last set it to, causing the system to continue to run in order to achieve the new set temperature.  

Faulty Fan Limit Switch:

If the settings on your thermostat are set to the correct temperature, the fan motor may keep on running even when the HVAC is not cycling. This can be caused by the fan limit switch getting stuck in the override position. Resetting the limit switch located near the blower fan will prevent the fan from blowing unless it is directed by your thermostat. 

Dirty Condenser & Condenser Coils:

In order for your home to cold down, hot air passes through something called indoor evaporator coils that are used to extract the heat from the air, before blowing the cool air out of the vents and into your home. Refrigerant travels through these lines that lead to the outdoor unit. It is then pressurized by the compressor before heading into the condenser coils, where the excess heat is then released. Dirt and other dust or debris can begin to collect on the condenser coils, preventing it from properly releasing heat from the refrigerant. If the condenser coils get too dusty or dirty, the HVAC unit’s cooling power is significantly reduced. Therefore, your system will continuously run as it strives to cool off each room.

If the outdoor condenser unit is blocked by dust or dirt, there is not enough air circulation through the unit to release heat into the atmosphere. Grass shavings, pieces of mulch, weeds, and other obstacles easily dirty up the fan, causing them to get clogged. This problem prevents the unit from producing proper air flow and the HVAC system will work overtime, desperately attempting to cool off your home. 

Frozen Evaporator Coils:

If your air conditioner is running, but you somehow still feel warm or hot air blowing from your vents, the evaporator coils may be frozen within the indoor furnace or HVAC unit. These types of issues can limit the evaporator coil’s ability to receive enough heat. This causes the condensation pulled from the air to freeze on the surface of the coils while the system continues to try to cool. This layer of ice on the evaporator coils doesn’t allow the refrigerant to absorb heating energy in the hair.  

Frozen evaporator coils can be caused by excess buildup on the coils, lack of air flow from a clogged air filter, blocked room vents, or low refrigerant. Evaporator coils also may develop a heavy layer of ice if the condensate drip pan and drain line below become clogged, causing the system to hold excess moisture.

Dirty Air Filter

A dirty air filter can limit air movement through your HVAC system, causing several other problems aside from preventing your system to stop running. When your air filter is clogged with buildup, the unit is forced to continue cycling air in order to provide enough cooling for the home.

Low Refrigerant Levels:

AC units are charged with specific refrigerant amounts to ensure proper cooling effectiveness for your home. If there is a leak in your refrigerant lines, damaged coils, or other faulty components, the refrigerant may be escaping from your HVAC unit which limits the refrigerant’s ability to help the air conditioner absorb and transfer heat. Your system will continue to run for hours on end as it desperately tries to over correct the issue. 

Low Fan Speed:

If your air conditioner’s blower fan speed feels lower or less powerful than normal, your HVAC unit will not be cycling enough cool air throughout your home. If this happens, your air conditioner will constantly keep running in an attempt to get cool air pumping through your vents. Dirt, grime and other debris may become caked onto the fan blades, slowing down its speed significantly, and restricting its operation effectiveness. 

Incorrect System Size:

HVAC units come in many different sizes and choosing the right fit for your home is extremely important for proper heating and cooling operations. If your AC unit is too small, it will not be powerful enough to heat or cool your home to the desired temperatures. Air conditioning units use up a decent amount of power, which becomes wasted energy and very costly. An HVAC unit that is forced to work overtime, trying to achieve temperatures in a home that is too large for its operation power, will result in unpleasant electric bills and inefficient heating and cooling throughout your entire home. Replacing a unit that is too small for your living space is the best solution for your home in the long-run.

Call FiveStar Plumbing, Heating & Cooling for Air Conditioning Repair Service Today!

If your air conditioner will not turn off and you are unable to fix the issue yourself, don’t wait another minute to give us a call. One of FiveStar’s certified HVAC technicians will come out to assess, diagnose, and repair the system issue and problem components or replace them right away! Call us today at (615) 382-8130!