Did the fan motor turn before you needed a compressor? If not, that may be the reason you needed a compressor. Does the compressor function OK? The fan should come on with the compressor. If the compressor works but the fan doesn't come on, you need to diagnose the fan. Check whether there's power and ground at the fan motor when the compressor is on. If there's power and ground at the fan connector, and the fan doesn't come on, then the fan motor's busted. If there's no power or ground is bad, you need to trace those faults to the source and fix them. You can also disconnect the fan connector and try supplying power and ground to the fan motor and see of it works.
If you need to go to a shop, find an A/C shop or a Buick specialist.
Here's a directory link for you: