Hey there,

I know little to nothing about thermostats, but was wondering if anyone could help me. I was wrestling a friend in the hall and we bumped into the thermostat the other night. Now it doesn't cool at all. The fan works properly, nothing is frozen up outside, so I think I bumped a wire loose in the thermostat.

I have two tubes with mercury in them, the one on the top is blue on the end. When I move the temperature back and forth, a metal piece in the blue one sparks! I am guessing this is not normal. There are 3 "prongs" of glass on one end where the three metal things stick into the tube. The one that sparks is the top prong and is the medium lengthed prong and a black wire is conneted to its prong. My guess is that this one is my problem. Where should this one run to?

Maybe its not this simple, but someone help me! I don't want to have to pay to get someone out here if it's a simple problem! Thanks!

Everything you describe, including the spark, is normal.

Try to operate it with that cover off. Does it work? If not, remove the couple screws holding it to the wall and inspect it closely for any loose wires. If you can't find a visible problem, you may have broken something internally that can't be seen.

Replacing a thermostat is definitely not something you need an electrician to do. You can pick one up for $30 and replace it yourself in about 20 minutes even if you've never done one before.

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Originally Posted by rickj

Everything you describe, including the spark, is normal.

Try to operate it with that cover off. Does it work? If not, remove the couple screws holding it to the wall and inspect it closely for any loose wires. If you can't find a visible problem, you may have broken something internally that can't be seen.

Replacing a thermostat is definately not something you need an electrician to do. You can pick one up for $30 and replace it yourself in about 20 minutes even if you've never done one before.

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It does not operate correctly with the cover off... I took out the screws and no wires seem to be loose in the back. Me and my friend bumped into it, but we really did not hit it THAT hard. I just can't see that we damaged anything very significantly. But also, we were running the AC hard that night, because it was hot because of so many people in my house.

Could I have blown some sort of fuse? If so, where would I find such a fuse? I found a breaker box out back that says "AIR" so I switched it on and off, but still no AC. Thanks.

There is the remote chance that your system encountered a problem coincidental to, but not caused by, the jolt to the t-stat. I'd get a new one and try it. If it does not work, then you know it's not the t-stat. You can return it... and unfortunately, call an A/C company out.

... or give this thread another day; we've got a couple excellent HVAC folk here that might pipe in. The A/C side of HVAC is not my forte.

Be sure the thermostat is mounted perfectly level. This is a must with mercury filled stats, look closely you should see a line built into the stat saying level,The spark you see is inside the tube, cannot harm anyone, and is normal. When you move the tube, you cause the mercury to make contact across the switch, caauing the heat or cooling to start.

If the stat is level, then you knocked the tube out of whack. The tube is held by a bimetallic strip, kind of like a spring, that bends to rise in temperature, this movement of the "spring" causes the merc to make contact at the exact temperature setting.

You may be able to jiggle the tube and spring back to its normal position, but it is delicate and you may not get it right.