Measure resistance across the 2 terminals on the pressure switch. It is screwed into the top of the filter/drier (right front engine bay "floor"). If pressure is OK (>~10 psi), the switch should be closed (<50 ohm). If pressure is too low, it will be open (infinity). BTW, you can install a better high & low "binary" switch for a later model, as I did, and with low refrigerant now is the time.

Your cheapest way out is to buy an R-134A recharge can w/ pressure gage at the auto-parts (~$20). Connect it to the low-pressure port (top hose, front) and read the pressure. Should have instructions to tell you if too low and you need to add, based on ambient temperature. Don't add too much refrigerant. You can save it for the future.

If you do have a refrigerant leak, it should leave oil around the leak. There are only a few fittings where it can leak and all have O-rings. They should have changed to HBNR O-rings (usually green) when changing to R-134A, but may not have. The toughest ones to change are at the expansion valve on passenger cabin side behind and below the glove-box.

I had a return (suction) hose leak in the middle and left a green oily mess on top of the air filter housing (1985 CA "trashcan" style). I had added green flourescent die. I replaced the rubber using my Master-cool ferrule crimper. If the shaft seal on your compressor is leaking, you might not notice the refrigerant oil if it sits in the grub zone like on a W123 engine.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans