Does anyone know why I would have no cold air coming out the vents even if the compressor came on and the A/C is running? I opened the hood and the clutch is engaged when I operate the A/C button in the cab. So this means that the low pressure and high pressure switches are working. So I neither have too little nor too much refrigerant in the system. Because if those switches were tripped the compressor would not engage. Correct?