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What's Causing Your Central Air Conditioner to Blow Room-Temperature Air?

by Feride Halma

Your central air conditioner is supposed to cool down your home, so when room temperature air starts coming out of your vents, you can bet that something is amiss. Your home won't cool down until you take action to address the problem. Sometimes, that may mean making a few quick changes on your own -- and other times, it may mean calling a service technician. It all depends what's causing your AC to blow warm air. Here are some of the most likely causes. 

A Dirty Air Filter

This is the first cause you should consider since fixing it will take less than a minute. Have you forgotten to change your air filter? Leaving the same filter in place for months on end can cause it to become overly plugged with dust. Much like you'd have a hard time blowing through a blanket, your air conditioner has a hard time blowing air through a clogged filter. This causes it to overheat, which may warm the air.

If you do not have a spare air filter on hand, have no fear. Even small, local hardware stores carry them -- and they're only a few dollars. Take your old filter with you to make sure you grab the right size.

Weeds Growing Into the Outdoor Condenser

If you replace the filter and the air coming from your vents still feels warm, then take a look outside. If there are any weeds growing into your condenser unit (which is more common than you might think), this could be causing the problem. The weeds tend to block the flow of air through the AC system, impeding the cooling process. Trim back the weeds, being careful to pull them out of the condenser as you do so.

Bushes growing into a condenser and brush, like fallen leaves, piling up inside of it can cause similar issues. If you discover anything in or around your outdoor air conditioning unit, remove it and see if that fixes your warm air issue.

Faulty Thermostat Wiring

Once you rule out the filter and weed growth, it's time to move onto explanations that require some professional assistance to solve. One possibility is that the wiring leading from the thermostat to your air conditioner is faulty. Your air conditioner may not be getting the message to turn on, even though you have the thermostat set to cool. As a result, the fan is running, but the AC unit itself is not even kicking on. 

Fixing thermostat wiring should only take your HVAC contractor a few minutes. In the worst case scenario, they may have to replace your thermostat, which will cost $80 or less for a basic model or up to $250 for a more advanced model.

Lack of Coolant

Another reason why your air conditioner is not cooling may be that the refrigerant has leaked out. The refrigerant is the material inside the condensing coil. As it expands, it cools the air that blows past it. If your AC unit leaks condenser, the cooling process won't work as intended. 

In most cases, your HVAC contractor should be able to refill your condenser coil with coolant, which will cause your air conditioner to start cooling again. They may also need to patch a leak in the coil. If your air conditioner is more than 10 years old, however, your HVAC technician may simply recommend replacing the entire unit since it should only cost a bit more than repairing and refilling the condensing coil.

If your air conditioner is blowing room temperature air, the problem could be big or it could be small. Follow the advice above, and you or an HVAC contractor from companies like A-1 American Services should be able to restore it to working order.