I have 2 a/c compressor in our bluebird bus 2008,one of the compressor dont wanna engage.I replace the 3 relay the a/c switch,circuit braker and still the same,,,,,pls. help!

check relay and fuses and a/c switch on front panel inside the car

Do you know how your starting system works ? Do you know about the starter relay ? All power comes to an through the starter relay . The park neutral safety switch is on the transmission. VEHICLE RELAYS Testing from the relay base If you have a anti-theft system problem the engine computer - PCM will not let the starter engage . Go to www.bbbind.com for a free wiring diagram of the starter circuit on your vehicle .

1) TEST the fuse+ relar of a/c
see the next steps and fix it. God bless you
If so, the compressor is working and the A/C system probably contains enough refrigerant to make cold air, so the problem is inside the HVAC unit. Replace the motor that controls the blend air door (this is a difficult job and best left to a professional since it involves tearing apart the HVAC unit -- about an 8 to 10 hour job!).
If the compressor does not engage when you turn on the A/C, see if it will run by jumping the compressor clutch wire directly to the battery (use a fused jumper wire). If the compressor works when you jump it, and the A/C blows cold air, the system contains refrigerant and the fault is likely a bad A/C compressor clutch relay or a bad clutch cycling switch or pressure switch.
If the compressor does not engage when you jump it, the problem is a bad compressor clutch.
If the clutch engages but the compressor does not turn (the belt will start to slip and squeal), the compressor is locked up and you need a new compressor.
If the compressor clutch engages and turns the compressor, but the A/C still does not blow cold air, the system is probably low on refrigerant and needs to be recharged

OOPS ! Now, it sounds like the A/C relay is constantly on. In the power distribution box by the battery, try swapping another relay for the A/C relay (which turns the compressor on), and see if it now stops. If so, buy a new relay. Good luck.

The trigger from the dash switch activates the relay which in turn switches on the solenoid pulley to engage the compressor to work. If this circuit is traced the fault of a open circuit can be found out. If there is no power in the fuse or relay then the main wiring must be checked.
Also a failure of the solenoid clutch cannot engage the compressor and so the circuit to this section must be checked.

the ECM supplies the ground circuit for the a/c clutch. the high pressure switch also needs to be closed to engage the clutch. when the low pressure switch and the high pressure switch are closed that completes the power circuit to trigger the relay.then the power on the #30 terminal can connect to the #87 terminal to send power to the a/c clutch.

THE LOW PRESSURE SWITCH
SYSTEM IS PROBABLY LOW IN FREON
TO CONFIRM LOCATE LOW PRESSURE SWITCH AND JUMP
THE TWO PINS IF COMMPRESOR ENGAGES THR SYSTEM IS LOW
DONT LEAVE IT JUMP YOU WILL BLOW UP COMPRESSOR
NEEDS FREON TO CARRY COMRESSOR OIL TRUE OUT SYSTEM

Is the solenoid clutch holding on to engage the compressor, if not the relay or the fuse or the sitch is not active. check the connection to the relay.
If solenoid is turning the compressor then there is no pumping and so the cooling does not happen.It can be failure within the compressor, needs an overhauling .

Did you try jumping where the Clutch relay plugs into the fuse/relay box ? Pin 87 & 30 are the compressor clutch coil power supply . If you look on the bottom of the relay you will see four set's of numbers 30 & 87 , 85 & 86 . If you take a piece of wire an jump 30 to 87 this will send B+ voltage to the clutch coil engaging the compressor . Is the PCM turning on the relay ?
The Trainer 40 When the compressor won compress

The clutch will not engage if it is low on freon. It has a high pressure switch and a low pressure switch which keeps the power from the compressor so no damage will happen. Have the freon checked.