97 Chevy Pickup A/c compressor won't kick in?

I recently put new A/C hosing unit in my truck and
then proceeded to fill the lines with freon, but the
compressor wouldn't kick in to cool I put 2 cans of
freon in and nothing! We swapped the relay
switches with others and worked just fine in the
other spots took a piece of wire and put it in in
place of the relay switch and then the compressor
would kick in, but won't with the relay any help???