Toyota Repair: AC compressor dosent run, static pressures, ac compressor

Question
I have a 1998 Tucoma v6 SR5 and when I press the AC switch the light comes on but the compressor does not appear (sound) to start. Is there some sort of relay or solenoid under the hood that could be dirty? If not any other reasons. Shouldn't the compressor "try" to run even if low on coolant?  Thanks for any help.

Answer
The compressor will not engage if the freon level is too low,the first step in diagnosing this is to connect a/c line pressure gauges to see what the static pressures are, if the freon pressures are too low the cause needs to be located, there is problably a leak in the system.