Where are the ac relays located, and how do you check then out?

You should bring your Buick in for AC diagnosis. That kind of problem can be identified rather quickly by an A/C tech. I'd start by confirming that there is sufficient refrigerant in the system to allow operation. If the A/C compressor doesn't engage on command, I'd test the wire supplying the compressor clutch for 12 volts. If there's voltage, its the clutch. If no voltage, I'd work backwards through the wiring diagram to find the electrical fault. Thank you, david@apexautoaz.com