I just drove down to georgia and it is beginning to get hot. decided to try and fill the refridgerant in my r134 converted 82 300d. i have only recently moved to the south and never cared for air conditioning until now so i know little about the system. the can of refridgerant says to make sure you put it in the lower fill fitting not the upper, however it seems there is only one obvious place to charge it, ie a fitting right on top, directly behind the radiator. there seems to be no other fitting, at least in plain view ( i'm sure ther is a discharge fitting, i just havent bothered to locate it.). My question is,: is this fitting in plain sight right on top the correct place to fcharge it up? And also, without a gauge, how much to put in? any help would be great. driving around in humid geogia heat with a two year old is driving me nuts!!

If you're filling from a DIY kit (in other words a little can), then you want to add refrigerant on the low pressure side of the system. Trace the lines. The high pressure side runs from the compressor to the condensor (radiator-like thing in front of the radiator, probably through a reciever/dryer). The low pressure side starts at the metering valve (or orifice tube, doubtful on this vintage), through the evaporator (another radiator-like thing, but typically buried in the dash and in line to cool incoming air for the cab), and back out to the compressor.

It sounds like you've located a pressure port for the high pressure side. That's not the one you want.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

In my 85 300D, the low pressure port is up high, pretty much front and center in the engine compartment. It has a blue cap. The high pressure side is buried down low on the passenger side of the engine. It has a red cap. You'll see it if you trace the line from the compressor under the engine and up toward the passenger side headlight. If you can't find it, that's OK. You want to charge into the low pressure side anyway.

Be aware that your system will be pretty sensitive to the quantity of refrigerant used. Over- or under-charging it will reduce its performance. There is really no way to know how much to add without some tools. You could just add little by little, checking for performance gains as you go.