My VT commodore has a problem with the a/c I can get the compressor to cut in by by-passing the relay but it will not switch with the relay in, the relay is ok, I thought it was due to no gas in the system but I have been advised that the system is block? and this is why the compressor is not working, I find this a bit hard to believe, does any one have an answer for this fault?

Sorry mate, missed your post there.
When you bridge your relay you are obviouly bypassing the switching circuit and applying power directly to the compressor clutch. At least this proves your compressor clutch is okay.
When there is no or low refrigerant in the system, the pressure switch will open the circuit to the clutch (A/C) relay preventing any engagement. If the clutch were to engage with no refrigerant in the system it's possible the lubricating oil, pag oil, would not be present either allowing the compressor to work dry. Bad!
Not at all a good way to test it but if you bridge the relay and the compressor cuts in, does the A/C work. For example: the larger A/C pipe leading into the dash (firewall) from the engine should be icey cold to the touch.
If so then the refrigerant is present. If not icey cold, the system is low on gas.
If you don't want to try this "dodgy" method then you need to find the pressure switch and bridge the correct terminals. With the A/C on the BCM (Body Control Module) will think there is good gas pressure and allow the compressor to engage.
Don't know what you mean by "block" exactly.
Generally speaking the only things that will stop an A/C clutch from engaging are:
Low or High pressure reading through the pressure switch.
An A/C compressor clutch circuit fault. Such as a relay...
Or a thermostat control preventing engagement. (not fitted on a VT)
Hope some of this helps.

Hi Kordorn,

Thanks for your advice, sorted out the gremlin as a blocked receiver dryed. replaced the receiver dryer and went back to the Aircon. man and charged up and work great, to bad summer is coming to an end

Thanks Wayno