Our AC stopped working today (no cooling) - got a reputable contractor to check the system and he found the outside units wires were blown (burnt out).

He provided two options:

1. Fix the wiring (for $1000) but was not sure that the unit will still work after that (its goldman brand 14 years old).

2. Got a Carrier 3.0 tonne builder grade ouside unit plus new coils insdide for $3900.

Am I better of going with a new unit? What could have caused the wires to blow up?

Thanks

$3900 is a reasonable replacement price, you will gain efficiency with a newer unit.

With that said $1000 seems a bit high to rewire a condensing unit, and with no guarantee it will work after repair.

I would lean towards the new unit.

The most common caused of burnt wires that I've found are loose connections or voltage issues.

He is ripping you off for 1000.00 just to repair wiring.

At this price he does not really want to fix your unit. He just wants to sell you a new one.
Depending upon your circumstances you might want to get a price from someone else for the repair and replacement. Never just take one bid on a job because you will never know if the person is being honest with you.