Where is the low side AC port on a 1999 Accord EX?

Just look for a valve on one of the lines with a plastic cap- near compressor or evaporator. Like a tire valve inside. It (cap) may be color coded blue. If not high pressure side will be larger diameter for safety anyway so a refill can will not plug into that one even if you try and if it does, pressure simply won't let contents come out of can. You only recharge on low pressure side