I had a landscape fire that melted the wires coming from the house to the AC unit. I need to purchase the proper wires to get the unit up again. The unit is a Nordyne ES5BD. The wires are coming from the house. But I don't know what to purchase or connect them to on the unit

Are you replacing the high volt and low voltage wire??

All the main wires are still connected to the unit (relay switch?). There is a small black wire and a small yellow wire that are not connected. They go down to the bottom left under the panel. This unit is 2.5, I also have a 3.0 ton. I looked under that panel and the black wire is connected to the white coming from the house and the Yellow is connected to the red. However, there is a green, blue, and orrange wire coming from the house but I don't think they connect to anything.

I have a funny feeling that someone splices wires inside the unit and changed colors on you. On a simple single stage AC unit only two wires are needed. When you take off the panels to the AC unit, there should be a main contactor with the power (BIG wires) and two smaller wires that come from the house.

These two terminals get connected to Common at the furnace and Y at the furnace.

4 conductor tstat wire is red, green, white, and yellow. Common was not run to the older stats. Blue is a typical color for common, but not to the outside unit because 10 conductor wire isn't usually run there.

You can splice outside or you can put a splice box on the wall with approproprite cord connectors on it.

Replacing the wire or splicing depends on what's easiest.

A location used underground wire and it also went through cement, so it was either a splice or a splice box when the wire had to be extended.

Heat shrink, solder and special tape that costs $1.00+ an inch or $35 for 30' with a drip loop was the solution.

Home Depot should have thermostat wire by the foot.