I have installed a new condensing unit and cannot get it to turn on or the furnace to operate in the heat mode. What voltage reading should I expect at the thermostat? I do not seem to be reading 24 volts and am not sure if it is the transformer as I did not touch it. I am wondering if the transformer went bad. The thing is that the fan goes on when the thermostat is pushed to the fan position. That is what is throwing me off. If the power was not available then the fan would not activate. Any ideas??

You can't measure 24 volts at the stat , since there is no return, or common, back to the transformer. The feed is usually the red, connected to R on the stat, and the heat switch leg should be the white connected to the W terminal on the stat.

Y is the terminal for the power to the compressor.

If this is all correct, you may have a defective stat.

Haing the fan start in fan mode proves there is power at the stat.

I have a carrier heat pump system. When I turn my unit to cool mode the 5 amp fuse blows and there is no power.