A/C Problem.

Hello,
I have a problem with my a/c and maybe someone can shed some light on the problem.

I recently had a new engine put into my 1999 Mazda 626, 4cyl., manual tranny. and my mechanic disconnected an a/c hose accidentally while trying to get the compressor out of the way.

Now, I bought some more freon and recharged my lines but my a/c still does not blow cold at all and summer is coming!!

Also, I noticed my compressor clutch engages about every 7 seconds and while I'm filling with freon i noticed the pressure on my can goes down to zero every time it engages.........I am not familiar with a/c components and am on a tight budget right now so a mechanic is last resort. Im thinking about getting the compressor rebuilt but i dont know if this is the root of the problem since it DOES engage.

I also want to add that I am sure the lines retain the freon and there is no leak.

Please help!!

thank youl