If they did not put in the exact required amount of refrigerant, but only a "minimal amount" then the system will not operate as designed and will not get cold. A full charge level is essential for the system to be able to transfer heat.
If the high side pressure is out of range there are several possible causes:
(1) Incorrect refrigerant type. This system was likely designed to operate on R-12 refrigerant (check for a label under the hood listing the correct type of refrigerant for the system). If someone has added an incorrect refrigerant such as R-134a, it will likely not cool as well as originally designed, and will probably be showing abnormally high pressure on the high side of the system.
(2) Cooling fan not operating: If air is not flowing through the condenser core, it will not be able to radiate the heat away and high side pressure will go through the roof.
(3) Faulty expansion valve or condenser: If refrigerant flow is blocked or restricted due to a faulty component, low side pressure will drop towards zero and high side pressure will keep going up untiill all of teh refrigerant is pumped into the high side of the system and trapped there.
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