Sounds like the hose was repaired to begin with. Not replaced with a factory hose. The fittings don’t have the barbs they used to have when we could replace just the rubber hose and use “A/C” style clamps. R134 runs higher pressure than R12 175-300 high side depending on engine speed,charge and ambient temp. Put on a factory Mazda hose the correct amt of 134 and make sure the condensor fan is running. Watch the gauges…350-450 is trouble on the high side and will blow off at the pressure releaf valve on the compressor…or find a shop with the right know how