For some time now my air conditioning has been warmer than it should be. So yesterday I bought a bottle of STP refill and the trigger gauge thingy. So I checked the pressure as per the instructions and it said it was a little low. So I refilled the system, again as per the instructions and all was well for half an hour or so, lovely and cold. But then all coldness ceased and when I checked the pressure (on the low side as that is all I can check) The pressure was so high it'd gone off the gauge! Also, I let a little vent (not much as I know it is a greenhouse gas) to see if I could reduce the pressure expecting what came out to be icy cold but there was no coldness at all, just warm air mixed with what I guess is the leek fluid additive in the refrigerant. All a bit weird really, not at all what I was expecting!