If when a compressor is replaced, the system is always evacuated, then pressure and vacuum tested after closing the system back up, and then, recharged with the correct weight of fridge gas, and the oil weight that was in the original compressor should have been weighed, then the new compressor's oil content corrected to be the same as the old one.
Then the system should be run to check for operation, not just for cooling performance, but also to monitor/check Hi side and Lo side running pressures, cooling fan operation etc.
Edit:- please understand that the fridge circuit is not charged up to a certain pressure, this gas is a relatively low pressure product, so as long as there is any liquid refrigerant in the system, with the engine not running, the system pressure will always be the same but vary with ambient temperature. If the system pressure rises under that set of conditions, some of the gas or saturated refrigerant will turn into liquid again.
System running pressures will vary with thermal load and the weight of refrigerant loaded into the system, too much refrigerant loaded in will end up with running high side pressure to be above spec and the pressure sensor will inhibit the chilling function.
Excellent, thank you. Compressor has been changed, pressure switch changed and it still don't work. The econ light takes longer to come on than before the compressor was changed. Before it came on straight away, now it takes about 4 seconds, hence I was thinking it may be low on gas.
Any suggestions are greatly accepted.
Have you checked the operation of the cooling fan, maybe check that and if not running when the AC is switched on, work out a way to check the cooling fan motor and if it is okay connect it directly via a fuse to the battery and if it runs probably at its fast speed, then switch the AC on and see if it stays on, if so, there will be a problem somewhere in the fan control system.