Our old thermostat decided to quit so I am trying to replace it with a
"Lux" Brand from Lowe's.

What's happening it the Heat will turn on if we set it to heat and raise
the temp, but the Air conditioning won't activate mo matter what.
Once when I turned the switch to FAN the circuit breaker cut power.

The Central air unit is fairly old... Here is a picture

http://img139.imageshack.us/my.php?image=img0119ib4.jpg


Here is a picture of the thermostat's innards and how we have it wired:

http://img528.imageshack.us/my.php?image=img0120fz1.jpg

Hopefully I won't get flamed as badly as I did in the other group.
The model is CAG1500
there are five wires: white, yellow, green, blue and red.