Pbcasterlin: I have and 87 R1500 262, 98 SL1, 06 Kia Sedona on which I've been managing a/c issues for a number of years. Converted the '87 to R134 about 10 years ago with simple flush (need to rinse out pump of mineral oil and replenish with PAG100), new dryer (134 rated), stock orifice tube and recharge by weight to 80% of R12 capacity. Charged thru low pressure port (next to dryer) with engine off. Recharge went smoothly with bottle upside down (delivering liquid). Worked fine. Had to repeat procedure about 6 years ago after factory original compressor (r4) gave up at about 75,000 miles. 'New' compressor gave up a couple of weeks ago. Replaced per above process and now working fine. I've used this procedure (except for R134 conversion) on the Saturn and two Sedonas before this one with satisfactory results.
I've got some original hoses on hte '87 shedding gunk into the system. Found a shop about 30 miles away that refurbishes a/c hose assemblies. I'm going to try one of the 'rising star' R134 replacements (actually a mix of butane and propane). The thermal dynamics are compatible with existing hardware. It's compatible with PAG oil (so no flush). A full chage by weight is considerably lower than for R134 for the same cooling effects. Best to charge by pressure (or temperature as described bewlo) with the engine running. Will post the outcome of my experience.
Interestingly enough, the butane/propane mix was a shade-tree mechanic's option back when I was a kid with the usual admonitions from the sage-mechanics about functionality and safety. There WAS a valid functionality issue . . . over the counter gasses are 'poluted' with mercaptan, stuff that makes it 'stink' so you detect leaks with your nose. See
https://tinyurl.com/296cg8hw I'm told that sulfur in this stuff does long term damage to your system's aluminum innards. Now, about 60 years later, the same mix of refrigerants is being offered on a large scale . . . pure gas that doesn't stink. We shall see.
By the way, another way to charge your '87 is by temperature at the low pressure line before it enters the dryer. You want just enough refrigerant to bring that line down to 35-40 degrees . . . that's what an expansion valve does for you in a more modern system . . . just enough liquid in the evaporator to avoid freezing. You can buy thermocouple thermometers with tube clamps really reaonable on eBay et. als. See
https://tinyurl.com/TCMeter Since you're working so close to the 'freezing barrier' you check your thermometer against an ice bath to check its calibration then adjust your target temp appropriately for charging. You could get a type K tube clamp but the stock probe works fine. Tape the tip to the ouside of your suction line just outside the evaporator box with several layers of electrical tape. I leave one permanently installed and coiled up when not inuse just to check the health of the system. The probes are cheap off amazon. I've got about a dozen. You can use this to monitor your a/c outflow temperature too.
