can't work out why my air con is not working..

had it regassed last year - was performing really well, but now nothing.

The compressor is kicking in and if I touch the low pressure pipes they do get cool but not cold, however the air coming through the vents is the same with air con on or off. There is a hissing noise from around the centre console too.

another regas needed? I'm thinking of doing it myself, as you can buy kits with a sealant in to stop further leaks.

The fact the compressor is kicking in shows there to be at least minimum pressure and a hissing in the pipes is a sign of poor gas mix so you probably have a very small leak

I would do a top up as you've nothing to lose if it's already performing poorly but read up on how to do it first and take note of the directions on the can carefully. There needs to be the right mixture of gases and there is a "sweet point" where the best efficiency is achieved. Too much or too little on either side of the sweet point impairs its ability to cool