i have an 2006 dodge ram mega cab diesel my problem is i got my a/c checked for freon and was told it was low they put some in and when they tried to turn it on my light stayed on but the clutch would not engage. they said i needed a new compressor. the comp is not frozen i can turn it by hand what i want to know is if i get a new one should i also get a new pressure switch. they said i got power to comp fuses are good any ideas on what else to check.thx