Where is my low pressure valve for recharging A/C?

Hi,

  My 1998 Eagle Talon AWD turbo a/c is not blowing quite as cold as
usual.  I have a can of R134 recharger but not sure where to hook it
up.  The can says to hook into the Low pressure line near the firewall.
 On my car the only valve back toward the firewall has a blue cap on it
with an "H" on it.  The line is cold and I could not find any other
valves like it around there.  Is my cap mislabelled or am I missing the
low pressure line?  Looks like a tight fit for the recharger hose to go
over this particular valve.  Any ideas?  Thanks.