Light Switch Turns off A/C


Old 07-02-05, 04:51 PM
Thread Starter
Join Date: Jan 2005
Posts: 76
Light Switch Turns off A/C

Since we moved into our house, I always wondered what the light switch did in the living room. It was marked "do not turn off" and had one of those protective things on it that prevents it from being turned off.

Well, today I finally decided to flip the switch to see what happens and it actually turns off the Air Conditioner unit up in the attic. After some further investigation, it appears the switch is attached to old Knob-and-Tube wiring.

The compressor on the side of the house is wired directly to the main panel on a 240V Circuit.

Should I be concerned with this unusual installation? Do you recommend I replace the Knob and Tube wiring with Romex and bypass the switch?

Just so you know, our home is 88 years old and was retro-fited with an A/C unit back in the Mid 80's. All the Knob-and-tube wiring was thought to have been replaced, but it looks like a few runs between the basement and attic were missed. Whoever replaced the original wiring ran romex to all the lower level and then spliced the knob-and-tube wiring to the attic and the romex together in electrical boxes in the basement. Judging by the date on the breaker panel, it appears to have been done around the same time the A/C was installed.

Thanks in Advance.

Last edited by wubears71; 07-02-05 at 05:02 PM.
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Old 07-02-05, 05:32 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
Replacing K&T is almost always a good idea where it is accessible. Most of the time you have only a partial replacement of the K&T, it's because only some of it was easily accessible.

There are a lot of conditional statements in your post, so make sure of what you have before changing anything. I'm kind of surprised that you have an air conditioner in the attic. Doesn't seem like a good place for it. It's probably just a blower unit, right?

I'd probably leave the switch as it is. You never know when you're going to want to turn it off if something goes wrong with the A/C.
Old 07-02-05, 05:59 PM
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Join Date: Jan 2005
Posts: 76
Originally Posted by John Nelson
It's probably just a blower unit, right?
That's exactly what I meant.

Thanks for the advice. I'll wait until fall when things cool down a bit to replace the K&T wiring. I need to run a new circuit into the attic for a new hallway light, so it will be a great opportunity to replace the last bit of K&T left in the house.

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