A month ago, I last traveled down to Phoenix, was 115F that day. I drove my 1998 Frontier to store to pick up Mrs. Cusser's Rx and noticed that the AC didn't seem to be working as well as it should be, but it was too hot to investigate those that day.
So I went back 2 weeks later, threw AC gauges on it - half expecting high side pressure to be low due to an R134a leak, but pressure was over 325psi at maybe 2000 rpm. I felt the low side schrader was leaking, and that maybe the cap was faulty too. I misted the AC condenser with water and high pressure dropped; so I rolled up some newspaper and checked the fan clutch, and the rolled newspaper easily stopped the fan. So I removed the fan clutch using my special ultra-long 10mm wrench and swapped it for a new fan clutch at O'Reilly, and installed that. The previous fan clutch lasted 47K miles. Next morning though, the AC was still performing sub-par, and previously had great AC.
Monday, there was still enough refrigerant in the system to engage the compressor, and low pressure line from evaporator wasn't even cold, and high pressure reading was lower due to new fan clutch. I hadn't added any refrigerant since 2017. Rather than spend time in 120F garage to evacuate the system to replace the leaking low side schraeder valve then pull good vacuum and refill from scratch (25 oz.), I chose to add 12 oz. of pure R134a (one can, the R134a capacity is listed at 25 oz.) and use a new low pressure valve cap (the real seal). AC looked good after that, good vent temperatures at least 45F leak checked the low side cap and found no leaks so calling it good.
So I'm figuring that the refrigerant leak was a bad low side schraeder coupled with a leaky low side cap. The cap is the real seal on auto AC systems. So I violated a cardinal rule of auto AC and just added refrigerant without knowing how much remained in the system, I know. But it worked assuming the replacement valve cap holds up.
