I second Lost1Wing. I have used both methods on numerous automotive A/C systems but have had better success finding very small leaks with dye and UV. If you are losing your freon charge in one day, you have a large enough leak that the sniffer should easily pick it up. Most common locations are fittings and joints. However if you still cannot find it, it is time to gain access to evaporator, as it is probably hidden in a plastic compartment.