Now that we are finally into the “WARM” St. Louis weather we have started getting requests for service to check out possible problems with residential electrical systems due lights dimming when the air conditioner kicks on.

In many homes, this is a “normal” occurrence. This happens because the lighting circuits share the same service as the air conditioner. When large motors such as air conditioner compressors start up, they require a higher voltage to “kick” them into motion. This is accomplished by electronics built into the air conditioner. This high voltage “kick” lasts only 1-2 seconds then the voltage drops to the normal 240V that the compressor is designed to operate on.

When this “kick” happens, it drains available electrical current to other devices on the same service. The result is seeing lights dim briefly. Sometimes older televisions would show the effect by the picture shrinking in size for a second. In fact every electrical device on the circuit is affected but you only notice the lights because you can see them.
It’s like a localized “brown out” but it lasts for a very short time.

There is no real fix for this other than to attempt to re-distribute circuits in your breaker box. But even this may not correct the problem.

Very rarely do we find a dangerous situation in the breaker box. If we do it’s either a breaker that is burning up or a loose connection. But 99% of the time, this dimming of lights an inconvenience and not a danger. As the air conditioner gets older, it gets harder to start and will even take more current to get it running. An HVAC contractor can check it and see if there is anything they can do to “help” it along. We can refer you to a qualified HVAC contractor if you do not have one already.