AC was coming on and going off after afew seconds but now nothing and no power to thermostate but power to unite
I would just get a new thermostat they are fairly easy to install and walmart or home depot has them cheap! I had a repair guy come out and I ended up going to walmart to get a new thermostat and I fixed it after the 80 $ repair bill which nothing was done!!
If you have no power to the thermostat you have a problem in the low voltage control circuit, 24 volts. It could be a blown fuse on the control board or a defective transformer provided the thermostat is controlled by the 24 volt circuit rather than operating on internal battries. If you are not getting power to the thermostat a new thermostat will not repair the problem. Remove the thermostat and jump the red and yellow wire togeather. If the a/c does not come on with the wires jumped togeather then you are not getting power from the transformer