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Cooper Mechanical Blog

Do Your Lights Dim when the AC Comes On?

Posted by: Cooper MechanicalTuesday, September 17, 2019

Lights dim when AC turns on

Lights Dimming When the AC or Another Large Appliance Turns On

If you've noticed your lighting dimming or flickering when the AC comes or when you turn on the vacuum cleaner, you're not alone. Although the quick dimming may cause concern, the good news is that it is most likely harmless.

Like starting a car from a cold crank, an HVAC unit takes a lot of power to start initially. The surge of power needed to turn on may temporarily drain electricity from other appliances like your lighting.

As long as the temporary drain is minimal (lights dim but don't go out) and short in duration (a second, for example) this is nothing to worry about. After the "cold crank," your unit requires less power to stay on, and lighting and appliances all receive an appropriate amount of power.

When Lights Dimming is a Sign of a Larger Problem

If your lights lose more than half of their brightness or go dark when an appliance like your HVAC comes on, it could be a sign of an electrical problem. Here are some potential electrical and HVAC problems that could cause your lights to significantly dim for longer than a split second:

Damaged Wiring: Loose or frayed wiring can cause current loss that is exacerbated when the HVAC turns on. This could definitely cause lights to significantly dim or flicker. 

Weak HVAC Capacitor: Your HVAC capacitor stores power to give your compressor motor a boost upon start up. Overtime, your capacitor's ability to store energy weakens, just as an old car battery does. A damaged, old, or weakened capacitor causes your HVAC to draw more power away from other appliances, causing light dimming.

HVAC Shares Circuit: If other major appliances share the same circuit with your HVAC system, your circuit may be overloaded. There may be light dimming, but if this is the case, you'd likely also deal with your circuit breaker tripping. An overloaded circuit can be a major hazard, so it's important to unplug high voltage appliances until they can be separated or a safe solution by an electrician is found.

An Electrical and HVAC Specialist

Cooper Mechanical Services is the Myrtle Beach area's solution for all things electrical, mechanical and HVAC. Often, HVAC and electrical issues are connected. Our professional electricians and technicians are highly skilled, honest, and dependable. If you are concerned about your home or workplace's HVAC or electrical system, call Cooper Mechanical Services today.