Buick Park Avenue 2000 model
Changed compressor and did not fix problem. Ac when turned on will only go to economy. Please Help
That's not enough information to go on.
Why did you replace the compressor? Sounds like there may not be 12 volts to engage the compressor clutch. If that's the case, there's a diagnostic procedure which involves the testing of several circuits, including data inputs to the PCM, along with the command circuit to the compressor.
You may be better off paying a diagnostic fee at a dealership before going any further.