Just to get started, try using a small split pin or wire to connect the two pins on the electrical connector going to the low pressure switch, this is found on the drivers side of the accumulator which in turn is located under the bonnet on the passengers side close to the windscreen. The acummulator is normaly black or silver. If when you connect this wire/split pin and then turn the car on and then the A/C is also turned on you find that the A/C compressor comes on (you can usualy hear the change in the engine and a load click) then the A/c electricals are OK and the system is down on gas. DO NOT LEAVE THE WIRE/SPLIT PIN CONNECTED!!!!! OTHERWISE YOU WILL WRECK THE A/C COMPRESSOR!!!!!!!!!
If this worked then you HAVE a gas leak, NO ANDS, IFS OR MAYBES....END OF STORY. Chances are on a VN (or most Commodores) is that the Evaporator (under the dash) is leaking or the compressor is leaking, either way it is big money. About $1000 on average for the Evaporator and a bit over that for the compressor if done correctly. Although you may find it is a leak at one of the o'rings....maybe the ones at the condensor!
You can't check the evaporator yourself but you can make a preliminary check on you compressor......Look for signs of a stain or oil on the very front of the compressor (not saying anything BUT make sure the engine is OFF!)and then on the join just behind the compressor's pully assembly. Also check the two hose connections for signs of stains or oil leaks and see if the hoses spin, if you can twist the rubber part of the hoses on the metal fitting.
I would recommend that you take it down to a GOOD A/C tech and get him to re-gas it and put NEW oil in the system and put some FLURO DYE in the system. This will 1/ get you up and running again, 2/ Allow the leak to be found and 3/ not cost a real lot until you know what is wrong. The system will still leak as you are not fixing it at this stage but it will help you find out what the problem is without wasting too much more money. (cost should be around $100 to do this)
The only other thing it can be is a blockage. If the compressor cuts in (without bypassing the pressure switch) but you get no cold at all it may be a blockage, or just very low on gas. Costs are dependant on what is wrong.
If you have any further problems just let me know and I'll see what I can do.
Oh and by the way $300 is not a complete overhaul, sorry, a complete system rebuild for most commodores can cost upto $2500 to do correctly. I would say that the last A/C tech you took it to only did a standard retrofit to your car and fitted a VP Condensor as they are more efficiant on the new gas (R134a). Check to see if he put dye inthe system. You might find a yellow sticker somewhere under the bonnet telling you this.
Kind Regards GUY.
