I think the control inside your home that turns Heat and A.C up and down is called a thermostat. Having said that I wanted to know if it is a big job to replace one? The one I have is only about 2 years old but it never worked right and I want to replace this one myself.
I do a lot of things myself. I just replaced a thermo coupling on my hot water tank. I like knowing how to do these things.

I hate to spend a lot of money to replace this as the last time the gentleman was here, he was working for about one half an hour and it cost a lot. I know I was paying for his knowledge but there is no reason I can't learn unless it is a really, really big job.
I think I can do this with a little help from my friends. Thanks

If you think you can or if you think you can't, either way you're right. I recently upgraded my old round Mercury type thermostat with a digital programmable unit from hunter. Really quite simple: just match the coded letters and go. Ence you pop toe front off you will see these letters. Just a standard screwdriver and maybe a flashlight. I would also recommend turning off the breaker to AC/Heat unit. Let me know if this is at all helpful.

Caption Rich, Thank you so much... I always think I can do anything and sometimes find out that I can't. I will have to buy the thingie ( kidding) and I will try to replace it myself. I never thought of a digital programmable one. Thanks for the idea.
I may not have time to do it for a few weeks but you can bet I put this post in fav places so I can come back and read it again when I have everything I need. Thanks again.

See my post about digital thermostats before you make me a hero. I had to call the manufacturer about the correct model number. I always say I can do anything and there is nothing I can't learn. Anyone who's an expert in their field started a rookie, too. Good luck and we'll look forward to hearing form you later.

Replacing one common 4 wire thermostat with another is an easy job. Still, you can run into some problems. If you look at the questions here, you will see many people do. What you need to do is go to the sticky at the top of the forum here and read about thermostat wiring. Also read the section on ''Do I have a heat pump?'' Many people get in trouble trying to replace a heat pump thermostat with one not meant for the job. Carefully note how the wires are connected to the old thermostat and read the directions for the new. It is also possible there is nothing wrong with the old thermostat except maybe wired wrong. The sticky also give a simple check for problems with the thermostat or furnace. Replacing the thermostat won't fix a bad furnace.

Once you understand what you have, you can post back with specific questions if you need to.

Thanks guys you have all been a big help. I know my air and heat is OK as I had it replaced last fall. As I said before I am putting this post in fav places for future references. I will read all before I attempt the replacement. This was my first step.

Labman you said something about heat pump and furnace, my heat and air is one big unit that sits outside.. it is not a heat pump or a furnace... does that make a difference?