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AC & Furnace Vent in a Palatine & Libertyville, Illinois Homes

With wavering springtime temperatures, you may not be surprised to hear both your air conditioner and furnace turn on in the same day. But is it safe to frequently switch between heat and cool? And what happens when your AC and heater start running at the same time?

Keep reading to learn 4 possible reasons your AC and heater are running at the same time.

Can You Switch from Heat to Air Conditioning on the Same Day?

Switching back and forth from heat to cool is perfectly safe. However, you should make sure that you let your unit complete its cycle before flipping the switch. Once the cycle is over, wait about 5 minutes before switching it from heat to cool, or vice versa. This allows the refrigerant in your system to return to its original pressure.

4 Reasons Your AC and Heater are on at the Same Time

In most cases, your furnace and ac will run at the same time because of an internal issue. Here are some of the most likely causes:

  1. Incorrect Wiring

If you recently had a new HVAC unit installed, the technicians may have incorrectly wired your new system. This incorrect wiring could be causing your air conditioner and heater to come on at the same time. This may also be the case if you replaced your thermostat recently. To remedy the situation, simply reach out to a trusted HVAC company to schedule an appointment to remedy the wiring.

  1. Faulty Thermostat

Another possible cause could be a faulty thermostats. Over time, the wires in your thermostat can degrade and the electrical components inside the thermostat may begin to malfunction. In these cases, replacing your thermostat is an easy and inexpensive way to fix your HVAC system.

  1. Defective Control Board

The control board manages a number of functions, including giving power to both your air conditioner and heating unit. A number of things can cause your control board to become faulty, including power surges, stuck relay switches, and loose wiring. If you suspect your control board is faulty, reach out to an HVAC expert for professional replacement service.

  1. Shorting Wires

In some cases, your HVAC system may be malfunctioning because two wires are touching each other and shorting out. This is usually an easy fix. Reach out to an electrician or HVAC professional to fix the wiring issue.

Schedule HVAC Repairs

If your heating and cooling system is acting up, Allied Air Conditioning and Heating Corp. is here to help. Our team has extensive experience dealing with malfunctioning HVAC systems. We always inspect your system before starting any repairs so we can diagnose the issue accurately.

We’re proud to offer honest and affordable repair services you can count on. For over 50 years, we’ve been the most trusted choice for air conditioning repair in Palatine and the surrounding communities.

Call us today at (847) 262-3349 to book a repair appointment.


Interested in a boiler for your home or commercial space? Allied Air Conditioning & Heating Corporation partners with IBC and Carrier brands to not only ensure the right fit for any demand but outstanding reliability and lasting performance.


Through our relationship with Wells Fargo Bank, N.A., participating HVAC dealers offer a variety of flexible options for financing your new HVAC product or system. That way, you can invest in your home’s comfort without breaking your monthly budget.

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