You’ve turned your thermostat off, but your outside AC unit is still running. Sound familiar? It’s a frustrating and confusing issue for homeowners, especially during the summer when your cooling system is already under heavy use. If your AC won’t quit even when it’s supposed to, there are several potential reasons behind the problem. Let’s explore the most common culprits and what you can do to fix them with ServiceOne Omaha.
1. Stuck Contactor in the Condenser Unit
One of the most common reasons an outside AC unit keeps running is a stuck contactor. The contactor is a switch inside the outdoor condenser that controls the flow of electricity to the unit. When the thermostat calls for cooling, the contactor closes to let power through. When cooling stops, it should open and cut power.
If the contactor gets stuck in the “on” position due to wear, corrosion, or debris, your AC will keep running no matter what your thermostat is doing. This is a repair that a licensed HVAC technician should handle.
2. Faulty Thermostat Wiring or Settings
Your thermostat acts as the command center for your HVAC system. If there’s an issue with the wiring, such as a short or a misconnected wire, it can send the wrong signals to your system, causing it to stay on even when it shouldn’t.
Sometimes, it's as simple as a thermostat that needs new batteries or has incorrect settings. Before assuming it’s a wiring issue, check the basics: Is it set to “off”? Is the display working correctly? If you’re still seeing problems, it’s time to have a pro inspect the wiring.
3. Dirty or Frozen Evaporator Coils
Dirty coils can block airflow, causing your AC to work overtime and the system to become unresponsive to normal shut-off commands. In some cases, restricted airflow causes ice to build up on the evaporator coils. When this happens, the system might continue running in an attempt to compensate.
While dirty coils won’t directly cause the unit to ignore the thermostat, they can trigger a cycle where the system can’t properly shut down. Regular maintenance, including coil cleaning, can help prevent this issue.
4. Malfunctioning Control Board or Relay
In more complex cases, a faulty control board or a stuck relay inside the system could be the issue. These internal electrical components act as the brain of your AC, and when they malfunction, they can override thermostat commands. This kind of issue usually requires professional diagnostics and replacement.
5. It’s Not Actually Off
Some systems have a setting where the fan can run even when cooling is off. If your thermostat fan setting is set to “on” instead of “auto,” the outside unit may continue to run intermittently or seem like it’s constantly working. Switch the fan to “auto” and see if that resolves the issue.
Call the Experts at ServiceOne Omaha
If your outside AC unit won’t stop running even when your thermostat is off, don’t ignore it. Left unchecked, it can waste energy, shorten your system’s lifespan, and drive up your utility bills. The licensed HVAC technicians at ServiceOne Omaha can quickly diagnose and repair the issue to get your system working properly again.
Schedule an AC service today at serviceone.com and stay cool without the constant hum of an overworked unit.