AC schrader valve core broken...what needs to be replaced?
 

the low pressure side schrader valve was leaking, so i took a bicylce valve adjustment tool and attempted to toghten it, but something metal down inside the valve snapped. do i have to replace the entire line, or is there a way to replace just the valve itself?

it depends on what you "snapped"
 

if you broke the flats that the normal tool turns on a schrader valve, you will have great difficulty removing the bad part. if not, you may be able to get it removed with the a/c charge still in the system. they make a tool for just this function, it has a long tool that fits inside a chamber with a valve on it to close off the freon flow.
any a/c repair shop should have the tool, or you can get one at any HVAC repair shop.
good luck.
John

Depending on what broke, you may have a hard time getting it out. The core removal tool mentioned will not work if the valve is broken I am almost certain.

A/C Valve Fix
 

I stripped the threads on my low side A/C valve and was able to avoid buying a new low side hose by using and adaptor valve from a local A/C supply house. A reliable ebay vendor is http://stores.ebay.com/Frosty-Freeze-A-C-Products-Company. On his web site he lists both straight and 90 degree adaptors(Part# CPS-AD36C ,Part #FJC-6092) that I believe will work.
I would describe your problem to him and he can offer advice. If you have converted to R-134 coolant, you may need different adaptors.These adaptors have valve core depressors on the female side,so they should allow you to leave the old, leaky valve in place and avoid opening the system. The valve core exchange tool is readily available online (approx$32,ACKits.com) but I went cheap. My adaptor valve has not leaked in 2 years of use. I suppose that the two valve cores in series will slow down your recharge time due to flow restriction. Hope this helps.