(1) Firstly we need to wire the A/c pump to engage manually.
All A/c systems run a high pressure switch and a low pressure switch. These are what
automatically engages and disengages your compressor clutch at idle or W.O.T.
one switch is on the pump, the other on the condensor cylinder usually beside one of your
headlights behind the grill.
high pressure switch
low pressure switch and the wire to by pass..the low pressure switch is right of photo ontop of the pump
In my case i by passed both, relying on the check valve on the cylinder to
maintain a safe high pressure.
basically you want to run a wire with a positive feed from a switch on the dash board
to the wire that engages the electomagnetic clutch on the
front of the A/C compressor. (this is what i did).
(2)For my cylinder/s i was limited for space, being turbo/intercooled with dual batteries etc...and being an SUV i didn't want the cylinder/s under the truck or in the cabin.
So i made room for them by stripping out the A/C radiator and electric fan, mounting one either side of the winch between the front crossmember and the bumper subframe.
The type of cylinders you ask...2x 4.5 kg fire extinguishers.
I pulled the trigger/handle assemblies apart and cleaned out the left over dry powder inside, then
removed the trigger handles and brass valve inside it.
I screwed a half inch fitting into the top of one with a T junction, one as the inlet and the other to be the outlet.....
the 2nd an inlet and a 1/2 inch line to the air coupling mounted in the grill.
these bigger fire extinguishers also have a 1/4 inch pressure safety valve screwed into the side of the trigger housing so may pay to fit either a small pressure gauge, check valve or blank it off.
(3) plumbing.... the gas used in A/C systems also lubricates the pump...we need to replicate this. in my case i cut the inlet pipe to the compressor at the fire wall and plumbed it in with a T piece to the pipe that runs between the Air oil seperator and the intake pipe that goes back to the inlet between the Air flow meter and the turbo charger.
Thus supplying a oily residue in the air for the pump to use as a lubricant.
the outlet pipe is also cut and a half inch fitting clamped/screwed into it with some 1/2 inch air line to carry the compressed air to the cylinder up front.
So all up i have a system that can charge a 9 litre volume up to 120 psi at engine idle in around a minute.
according to this fancy calculator http://www.1728.org/boyle.htm it equates out to around 73 litres compressed...
...I think(I'm no physicist)
All up the plastic T fitting and hose clamps came from bunnings $10
the air line i had laying aroung but its like $1.90 a meter
check valve/ T pieces air connectors $46.50
15 m flexi air line and tyre inflator(with gauge) and incorporates a deflator valve on it $25 from supercheap.
The Electrical wire is from an old extension cord with a 30 amp fuse (Didn't really know how much current the
clutch on the A/C pump would draw but hasn't popped the 30 amp fuse yet.)
I would suggest you pop into an automotive aircon shop with a box of beers and ask them to crimp your hose joins as those hose clips may just fail, there can be massive pressure applied before the pressure switch kicks in. I know from experience with the jury rigged system I had in my shed off my mains powered air compressor before a hose joiner blew. 
, there is no need....it took under a minute to compress 70 odd litres of air to 120 psi.
I've been adding a squirt of oil to the intake pipe with an oilcan occasionally until now 
