AC compressor clutch not engaging

[jfnar]

The clutch on the compressor sometimes engages only for a few seconds and then releases, other times it doesn't engage at all. I unplugged the connector at the compressor and it's getting 12V and there is continuity to ground on the compressor side. I've never worked on AC other than adding freon and checking pressure switches. Is this likely to be a bad compressor? Any help will be appreciated.