?

Since you indicate you don't know the original refrigerant being used, nor the quantity, ?its going to get a little difficult.?

?

So, the question is how to proceed with what you've got... Hmmmmmmm

?

My best suggestion is a source of R-22 freon (or its environmentally friendly equivalent)

?

R-12/R-124a might work, however the system won't get as cold given the same low side pressure.? However R-124a is available at any Wal-Mart or?auto parts store...?

?

In any event the best course of action might be to just pick a handy refrigerant and give it a try!?? Pull a modest vacuum on the system,??fire up the compressor and watch the low side pressure.?Next add JUST A TOUCH of refrigerant, and what you want to achieve are two things

?

#1 Liquid refrigerant going thru the Cap Tube (just listen to the system, liquid refrigerant will sound different than gas flow thru the Cap tube, I avoid attaching gauges to the high side of a freon system but you could do this and note the Pressure/Temp relationship and calculate if your getting a liquid)

?

#2 The lowest low side pressure possible, while still maintaining item #1 :)

?

If the above doesn't get cold enough for you, either increase the length of the Cap tube, or decrease it's internal diameter.

?

On my system, I used just a "Squirt" of R-22, a dang near totally closed valve, ?and my low side actually runs @ -10 inches of mercury as displayed on the HVAC gauge set during?"normal" operation.

?

BTW, if you have to guess on a Cap tube length, Guess LONGER than you think.?

?

Also, a trick you might try If you find the low side pressure is still higher than you want, gently crush the cap tube with a vise, in effect decreasing its internal diameter. This will add increased restriction to refrigerant flow, lowering the low side pressure/temp.? Only problem with this idea is if you "Over do it!" :)

?

Best of luck!? BTW, have any pictures???

?