compressor noise

i just had to replace my engine on my 99 gp gt (only 50000 miles) and when i picked it up i turned the air on and now there is a humming and some vibration when the compressor is engaged. it never did this prior to getting the engine replaced. if anyone can give me an idea why and if it will do any damage because i dont feel like paying $80 an hour for them to say nothings wrong. btw the car sat with no engine for close to a month so could that have something to do with it?i appreciate anyones help.

it's possible that moisture got in the clutch bearing and it got some rust on it. Was the A/C compresor unhooked when the engine was removed, or did they just unbolt it from the engine and leave the hoses hooked to it?

i honestly couldnt tell you. the mechanic who worked on my car called in sick the past two days so i couldnt even ask. also i tried to put some r134 with oil in it to see if it just needed to be lubricated since it hasnt been used in a month but i cant get the gauge from the can to go over the fitting (next to the air box), do i need to get an attachment for it or do i somehow have the wrong refill kit.

the low-pressure service port (where you add the refrigerant) is back on the firewall where the lines go through to the evap core, that's why your fill hose doesn't fit (the high side fitting is larger, so you can't hook up the wrong one and injure yourself). Did your mechanic install a re-man engine, or one from a bone yard. If he installed a bone yard engine, he may have used the tensioner from that motor and that's where your hum/vibration is coming from (it may have a weak spring).

it was used.i got it through the dealership.