Can I guess you mean the Air Conditioning Receiver dryer?
If so there could be a pressure switch on the receiver dryer for your aircon, it may have been disconnected or bypassed at some stage, the other end normally could connect to the compressor.
It depends how the car is wired up I have seen aircon wired up a few different ways.
Basically you have a thermostat to control aircon temp, pressure switch in case it runs outta gas, the clutch on the compressor, an idle boost solenoid, blower fan, and the aircon core fan. There are other poarts but im talking basics.
So for the air to work, there has to be pressure in the aircon system, be warm enough for the thermostat to work and then the compressor is allowed to engage.
You may find a pressure switch is on the aircon pump so the one on the receiver dryer would be redundant.
cheers
Scott
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Cheers mate i'm sure its an air con wire to now, which i don't have air con anyways.. i do but i don't![]()
I only came across it when i was doing the timing on my baby after installing the headers which i might add mate, great site your hose pictures worked like magic, my engine bay area looks alot cleaner and neat then before.