[Nervosa]

My central air isn't kicking on and before I have someone come out to look, id like to make sure its not something simple.

This started two days ago. I went to switch the thermostat (simple comfort 2001) over to cool and nothing happened, a few minutes later the display went dim.
I thought I blown a fuse so I checked the furnace and I did, so I replaced it.
A few minutes later, something. After blowing about 6 fuse I noticed the following things.

When the thermostat is set to heat with the fan on auto or on its fine.
When I switch the thermostat to cold (no matter what the fan is on) I blow a fuse.

Is it my thermostat, central a/c unit , something else ?
Anyone have an idea what it could be or what I could try to do?

[hvac1000]

Could be a wiring defect. Could be a relay. Check all electrical circuits for the furnace or A/C. If not capable of that call a pro. BTW what fuse are you talking about?

[Nervosa]

There's a fuse in my furnace. Every time I switch the thermostat cold this fuse gets blown

[letmetellu]

Check the thermostat wires on the outside of the house where thy go to the AC. Look for a place that they could be shorted together. If they are not in a conduit look for dog teeth marks along the wire, if you have a dog.
Inside the AC unit there are two small wires, that is if you only have an AC and not a heat pump, These wires should be connected to two other wires with wire nuts, unscrew both wire nuts and disconnect the wires, remember which wire was connected to which wire.
Now turn the thermostat back on and see if it blows the little fuse. If it does not blow the fuse then your wiring is OK but you have something wrong in the unit itself most likely a contactor coil that has shorted out.. Let me know what you find.

[Stratmando]

It does not sound serious.
Another way to say.
When thermostat is set to cool, 24 volts go out to contactor coil, powering up compressor.
Carefully remove 2 small wires going to contactor.
Go back inside set to cool, if fuse does not blow, Likely contactor coil shorted.
If fuse still blows, then 2wires coming from inside unit likely shorted.
Disconnect 2 wires from inside unit(That go to outside) set to cool.
If fuse doesn't blow, short likely between 2 units.
You are talking about the 240 volt to 24 volt transformer fuse?
If not, Will provide different answer, Compressor, or shorted wire between contactor and
Compressor.

[T-Top]

You do have a low voltage short some where. Look down inside the A/C unit make sure no wires are rubbing against the refrigerant lines(Low pressure switch- High pressure switch-Reversing valve if it's a heatpump). Check the thermostat wires going into the A/C unit to make sure a animal has not chewed on the wires.