a/c trouble in 97 civic

Hello all,
I have a 97 civic EX and last month my A/C went out when I was driving.
I checked both the fuses inside the car, and under the hood and that checks
out. My step-father was up over the weekend and he hooked a wire directly
from the battery into the A/C compressor, and the A/C started working in the
car. We tried making a temporary fix by putting alligator clips at the end
of the wire and having me just attach before I drove the car, but we soon
found out a couple days later that this caused the A/C to build up too much
pressure, and it would start to make a whining noise when I was driving
around. I have since stopped using the wire method. Since the A/C works
when direct power is applied to the compressor, do I need to buy some type
of relay? If so, what is the specific name of the part, and is it fairly
easy to change? Thanks.