AC Troubleshooting: Home Air Conditioner Starts Cold Then Gets Warm

image of homeowner feeling hot due to an air conditioning system that blows warm air

A properly functioning air conditioner is the hero of the hot sizzling summer months. If it performs well, it will cool your home to a set temperature and keep it there. Unfortunately, even the best plans go awry, and you may find yourself in a situation in which your AC unit is not performing optimally. For example, when your cooling unit first kicks on, you may notice that your home air conditioner starts cold then gets warm. This indicates that something is wrong. When trying to keep cool, this can be frustrating. Knowing this is the worst possible time for an AC failure, immediately finding a solution is the only course.

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AC Troubleshooting: Air Conditioning Starts Cold But Gets Warm

Until the temperature of your home reaches the temperature you have set on your thermostat, your air conditioner should be putting out cold air. Once the air in your home reaches the set temperature, the system should stop. At no time should it put out warm air. If it starts with cold air that transitions to warm, don’t suffer in silence. Contact an HVAC professional who will get to the bottom of the problem and remediate it in a timely manner. Sometimes, all it will require is a quick fix.

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Common Sources of Warm Air Blowing from An Cooling Unit

Below, we discuss some of the causes of an air conditioner that blows warm air.

Thermostat Problems

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The thermostat is what runs the air conditioning unit. It dictates when it should start a new cooling cycle. It keeps the air conditioner in operation until the ambient temperatures reached. Then, it tells it when it should shut off. At the onset of your problem, check your thermostat. Has the setting or programming been changed? It is not beyond reason that someone inadvertently changed its program, and you were not aware of the change. You should next check the thermostat’s battery. A low battery can make a thermostat behave incorrectly. If both of these factors are as they should be, there is always a possibility that it may be a legitimate thermostat malfunction that requires a replacement or professional touch.

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Air Filter Maintenance & Problems

image of a dirty air conditioner filter that needs replacement

It is important to replace the air filters in your HVAC system. The very nature of their job makes them less effective over a period of time. Replacing a filter is a relatively simple job. How often you run the system will dictate how often you should change the filter.

In warmer climates in which a system is used more consistently or in a home with pets, a once-a-month HVAC filter replacement is a good idea. For a less used vacation home, a change every six months may suffice.

A dirty air filter doesn’t allow air to flow freely. Impeded airflow puts a strain on the blower and other parts of the unit, making a dirty filter a source of inefficiency as well as prematurely worn-out parts. Occasionally a homeowner will realize their air conditioner filter is dirty and they don’t have a new one on hand. Some choose to go without a filter in an effort to hurry things along. This is not wise. With no filter, all of the dirt that should be kept out of the system is free to coat and corrode components.

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Low or Leaking Air Conditioner Refrigerant

Without refrigerant, an air conditioner simply will not work. The refrigerant cools the evaporator coils, which in turn pull the heat and moisture from the air before it is sent through the home. When there isn’t enough refrigerant for the job at hand, the heat can’t be drawn out. Sometimes the refrigerant level is so slow there is a chance the evaporator coils will freeze, and they will be usable to function properly.

HVAC Ductwork Problems

hvac air ducts

The blowers of your air conditioning system push the cold air through the ductwork that carries it through the rest of the house. If the ductwork is damaged, or has a leak, the cold air will leak out. The cold in the duct may dissipate before it reaches rooms that are the farthest away from the source. The result will be lost cool air and a weak trickle of warmer air at best. Dirt that has accumulated in the ductwork will act in the same way, impeding the cool air. Aside from a less cooling effect, if the warmer air reaches and impacts the thermostat, the system will have to strain to maintain the programmed temperature. The added strain can shorten the life of your air conditioner. For these reasons, it is wise to have your ductwork checked periodically.


Evaporator Coil Problems

As with the filter, it is important to make sure your system’s evaporator coils are clean. Dirt-covered evaporator coils can’t efficiently remove the heat and humidity from the air, making the system less effective or, even worse, freezing the coils and making them completely ineffective.

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Electrical Malfunctions

Have a professional make sure you have an adequate supply of power for the different parts of your system. If one component doesn’t get the power it needs, all components will not work together efficiently.

An Ounce of Prevention

image of an hvac contractor performing an air conditioner tune-up

Hopefully, with conscientious care, you will never have to deal with the discomfort that comes with an air conditioner system that blows warm air. There are steps you can take to help prevent this:

  • Filter Replacement: Remember a dirty filter cannot do its job. Dirty filters are the most common obstruction to free flowing air in the system. Have spares on hand, check for dirty build up, and change them frequently. You may need to change your filter as often as once a month.
  • Air Conditioner Maintenance: It is a good idea to make professional HVAC maintenance checks and cleaning a habitual part of your spring cleaning. By making it a regular event, you will always be ready for those blistering summer days when the system will have to operate at peak efficiency. A skilled technician will be able to recognize any potential problems and put an end to them before they become an issue. They can clean the system, lubricate moving parts, and check levels for optimum performance. An annual air conditioner check will extend the life of your unit.
  • Landscaping: Keep your outdoor air conditioner components in mind as you plan your landscaping. There should be at least two feet between vegetation and all sides of your unit. Regularly check for and get rid of leaves, sticks, and other debris that may have accumulated on top of and around the system.
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If & When Your Air Conditioner Blows Warm Air

If, despite your efforts, your system blows warm air, try the suggestions listed above. Finding the source of the problem may be more than half the battle. Try solutions you are able to handle on your own. If these don’t bring about the desired result, call a reputable HVAC professional before the problem changes from a simple fix to a major one. Most of the time, a speedy response to a problem will save you money, time, and stress. However, a slow response could lead to the need for a new cooling system.



Air conditioners cool the air, they do not add heat. If yours is producing heat, something is wrong. Don’t procrastinate. See if you can find a solution, but don’t take too much time. If your efforts fail, promptly contact a professional HVAC service provider. They will have the training, knowledge, and skills to take troubleshooting to a new level. This will save you stress and extra money down the road.

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Call Lawes Company For HVAC Repair Requirements

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Lawes Company provides advanced heating and cooling services for residents of Monmouth and Ocean Counties, New Jersey. By working with us, you are assured of a certified technician who is able to provide excellence in HVAC tune-ups, timely repairs, professional installation, and more. All of our techs have the knowledge as well as the experience to service HVAC systems correctly.

Lawes Company guarantees competitive heating and cooling costs. Our maintenance service is sure to improve your comfort, increase energy efficiency and reduce home heating and cooling expense. If you need an HVAC repair or a replacement system, let us recommend the best solution for your home while working within your budget. Our company backs our work with a guarantee to ensure your satisfaction. If you are ready to schedule an appointment, just pick up your phone and give Lawes Company a call. Ask us about our free, in-home estimates.

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