My ac needs new refrigerant, but alas my owners manual is no help as to the location of the low pressure recharge port, seeing as the AC is an aftermarket upgrade. I'm pretty certain this is an R134-a system but if I've made a mistake please correct me. The port under the blue cap fits a standard quick connect adapter.

In any case, I have included pictures of the AC system in question (let me know if the pictures don't show enough, i can take more), if someone could point out where I am supposed to recharge the system from, that would be a huge help.

 

This is not aftermarket, just a conversion to 134... If the port fits a 134 fitting, then someone did convert it, pretty safe assumption, so treat it as such... A '91 came with R12. Assume you have a leak, so don't just charge it and hope it will be OK. In 99% of the cases of non working AC systems the gas leaked out and that made the air inop.

 

thanks for the clarification, I didn't get too much info about this car when I got it. I understand it is most likely a leak, however seeing as I don't have the money for any amount of air conditioner repair, but I do have a leftover and unused can of r-134a refrigerant and a charging hose with a pressure gague, I was hoping to just have a quick fix until I can afford something more permanent, as well as just the experience of doing it.

 

Well then, you can always throw that can in to see what happens. Have you tested the compressor at least, make sure that it engages? If your system is empty the compressor will not turn on, you'd have to jumper it at the switch to see if it engages. And if your system is empty one can won't do it at all, you need around three 8oz cans to get a working A/C...

 

and you really want to charge it when its got a hard vacuum inside.