Is your Vitz with a 1.0 litre engine or the 1.33 litre engine? There are two different types of AC compressors. If you can look at the actual compressor and tell me which Denso compressor you have, I might have a solution for you. Is your AC working fine otherwise? One thing you can do to check if your R134a refrigerant gas is full, is to check the H pressure sight glass, which is located next to H plastic cap on the left side of the engine (when standing right in front of the car). If the glass has bubbles in it, then the gas charge is low. If there are bubbles, there is a high chance that there was less refrigerant gas in the system, that has caused the AC compressor to overheat and you will need to replace the compressor.