Assuming that each can you put in is 12oz, then the amount of charge is correct. R-12 charge for E30 is 2.15 (+/1 .05 lb. R134a should only be charge to equivalent to 80% of normal R12 capacity. However, your pressure are a bit too high. You suction pressure should be around 26 psig and high side below 200 psig. The reason for these readings are as follows: 1. At 28 psig, the saturation temperature for R134A is 30 Deg F (approx). That is the temp u want in the evaporator coil to produce air temp of 40-45 Deg F coming out of your vents. 2. The discharge pressure is way too high. Condensers are designed to operate at 30 Deg F above ambient. Assuming that it's a 90 degree day, a 120 Deg condensing temperature should indicated about 160 psig.