On Wed, 26 Sep 2007 00:35:23 -0700, wrote:

I would like to replace my thermostat in my apartment with a digital
programmable thermostat.
I don't have access to turn off the electricity to my HVAC system and
I don't want to involve the landland (I can always change back the
thermostat when I leave).
Do most thermostats run off of a 120v power control? Is there any safe

No. They run off of 24 volts. If you want to make sure, measure
before touching the contacts, but they do. And so will the
replacement thermostat.

way to replace the thermostat without being able to cut electricity to
the HVAC?

All the thermostat is is a couple electronically controlled switches,
plus an internal microprocessor. You should be able to take off the
old one and put on the new one without touching any of the uninsulated
portions of the wires and without letting any wire touch any other.
Heck, some people change 110 volt fixtures without turning off the
power.

If you do touch the wires, you probably won't be able to feel 24
volts, and it won't kill you.

If you let them touch each other, I don't think there is any pair that
will hurt anything. More likely it will start the heat or ac.

But now is the time to learn how to do these things wihtout touching
anything.

Make a detailed drawing of which wire is on which screw now, so you
can put it back before you leave, and so you'll be able to figure out
how to attach the new one.

Thanks