The receiver/dryer is about the size & shape of a beer can. Usually sits somewhere towards the front of the engine compartment. It has a dessicant to trap moisture so it doesn't screw up the system. Yours has been open long enough to suck up moisture from the air, making it worse than useless. I'd get a new one, but it's pretty easy for me to tell you to spend your money...

I don't know when Honda switched from R-12 to R-134a, but '90 might have been the old stuff. If it came with R-12 your R-134a hose won't fit. If it's been converted, the adapter fittings look like add-ons, not like they were built that way.