Your furnace and AC use the same air blower. Your home thermostat activates, controls, and shuts off both devices. The furnace and air conditioner work together to clean and condition air before recirculating it throughout the house. Both systems help maintain temperature and humidity.
The air conditioner will sit outside the home cooling while the furnace works inside the home to heat with fans and coils. Both systems use your home's ductwork and vents to transport warm and cool air. Alternatively, a heat pump and an air handler might be paired together to form a complete system.
Your furnace and your air conditioning system are two central components of your HVAC system, connected and controlled for greater efficiency. During warmer weather, you'll need to turn off your furnace and use your air conditioner instead. Your central air conditioning system is independent of your furnace.
In most cases, your furnace and ac will run at the same time because of an internal issue.
Air Filters
Even though the furnace is not producing any heat while operating the a/c, it still delivers the cold air throughout your home with the same blower, and passing through the same air filter. This is why, regardless of the season, you should regularly change your air filters.
While many people refer to air conditioning and furnace filters as if they're different, this is not the case. Your furnace and your air conditioning system use the exact same filter, so there's no need to worry about purchasing separate filters for each piece of equipment.
The short answer: You can get away with running your AC without a filter for a short period of time. However, doing so for longer than 6-8 hours can hurt your system and decrease your home's indoor air quality.
Take a look at the control panel connected to the split system. In many cases, the switch that activates the heating or cooling has a dual purpose. It could be in the wrong mode, which forces the AC to work instead of the furnace.
A lot of our customers ask us if it's bad to switch back and forth between their heater and AC, and the answer is no, as long as you're doing it correctly.
Always Wait for your Unit to Finish its Current Cycle
Always wait until the current cycle has finished before switching from AC to heating and vice versa. If you switch while it's still cooling, the outside unit has to work harder to get the house warm again. This can lead to premature wear and tear on your unit.
Furnaces typically last about twice as long as air conditioners, so they may still be going strong when your home's AC unit gives out.
The most important and most obvious step in switching from your furnace to your A/C is to turn off your furnace. Most modern heating systems can be turned off straight from the thermostat, but if you have an older model you may have to turn off the gas supply.
If the home includes an electric furnace, that unit will also have its own dedicated breaker. Issues such as low airflow due to a clogged air filter, obstructed air vents in rooms, a failing blower motor, or internal electrical defects inside the unit may be the cause of breaker trips.
Your furnace and AC use the same ducts, but they're independent utilities.
First, check your filters and coils for dirt and debris that may be impeding airflow. Once you've cleaned the filters and coils, run the air conditioner with just the fan so that the ice accumulation can melt off. If the AC still doesn't blow cold air, it could be that refrigerant levels are too low.
Air conditioner + furnace matched systems
An air conditioner and furnace is a popular matched system throughout the United States, because it can be paired with a high efficiency air conditioner, and provides significantly warmer air to the home.
The cost to replace a furnace and air conditioning at once is $7,500 on average but could range from $2,500 to $15,000. If your air conditioner has quit, but the furnace still works (or vice versa), it's tempting to just replace the appliance that's broken.
The first step is to make sure the thermostat setting has not been changed. Make sure it is set to auto or heat. Occasionally, a thermostat will be set to cool instead of heat, which causes the problem. Once you switch the thermostat to heat or auto, your heater should start right up.
The only situation in which it isn't advisable to replace both systems at once is if either your furnace or AC is less than 10 years old.
Insufficient insulation: Without adequate insulation, conditioned air will escape through gaps and cracks in walls and ceilings, leading to temperature fluctuations that create hot spots.
Therefore, your furnace blowing cold air could result from a clogged or dirty air filter. If you have a dirty or clogged furnace filter, the cool air from inside your home will struggle to travel through it and into the furnace.
In other words, your central AC is independent of your furnace. The outdoor unit isn't connected to the furnace at all — but they both use the same distribution system (vents, plenums, and ducts) to cycle cool air into your home.
You'll often find the filter in a slot or compartment within the air handler itself or near where the return air duct connects to the system. And that means, of course, that both systems share the same filter. So, air will flow through your system's air handler regardless of whether you're heating or cooling your home.
How Often Do I Need to Change Out My Air Filter? Generally, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days, or 3 months. That can change based on where your home is located (ex. dusty, dry climates), if you have any pets, and the age of your system and equipment.
There are a number of reasons why your AC unit may stop working unexpectedly, including electrical problems, blockages, thermostat issues, and more. Troubleshooting includes checking your circuit breakers, thermostat settings, and replacing your air filters.