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The thermostat is set to cool with the temperature set lower than the room temp. but nothing comes on including the indoor fan.
Check that your indoor furnace or air handler has power. Furnaces have a regular 120v “light switch” style switch near the furnace area. Electric air handlers have a 240v disconnect box with a pull out piece or a double pole breaker inside. In your home electrical panel box a furnace will be controlled by single pole 120v breaker and an electric air handler is controlled by a double pole 240v breaker.
Check control board fuse: There is a 3 amp fuse (like you would see in a car) on the circuit board of most furnaces and some air handlers. This fuse usually blows when there is a short in the low voltage wiring. This fuse protects the expensive control board from damage when 2 or more low voltage control wires touch. If you have electrical experience, you can follow the next steps. Contact a local HVAC contractor if you do not feel comfortable or do not have electrical experience. If this fuse has blown, first check the low voltage wiring around your outdoor AC. If a dog chews on these wires or a “weed wacker” hits them they will short out and blow the fuse. You can also check other areas where the wires run like squirrel damage in an attic or crawlspace. Once you find the damaged wires, make sure your indoor and outdoor unit’s power is turned off at the panel box, repair the wires with new wiring and wire nuts, and replace the on-board fuse. You can only use up to a 5 amp fuse, any higher will damage the control board.
If you have power to the indoor unit but nothing comes on at all, you may have a thermostat issue. Replace thermostat batteries. Remove the thermostat cover and make sure that all the low voltage wires are connected properly.
How to Replace a thermostat: click here for install guide