Unless your dad’s AC also doubles as a heater, then no, that’s definitely not normal. It could either be a problem with the compressor, or your AC is simply low on refrigerant. If you’re using a split-type unit, it’s also possible that a faulty return duct is sucking in unconditioned air from the outside or from your attic. It could be anything, really. It definitely sounds like the unit needs servicing.
I would suggest that you have a repairman inspect your unit to see exactly what the cause of the problem is. Go online and search for someone who does air conditioning repair in Tunbridge Wells
. I’m sure you’ll find a lot of repair options to choose from. Until then, though, I advise against turning the unit