My AC isn't cooling like it should again. Last year it was the low pressure switch. I replaced it again since the symptoms were the same but it didn't fix it this time. On the highway the compressor cycles about every 6 seconds. I can short the low pessure switch and it will cool fine. I just put the gauges on it and the pressures were 25-40 psi between cycles and 130-150 psi on the high side. The ambient temp and humidity is 77 and 60%. I am thinking it is low on R134. Does anyone know what the pressures should be and how much I need to add?