R134 can't be charged by using a sight glass because the liquid stream still will still have bubbles on a full charge.

Make sure you have enough air flow through the condenser ( Aux fan , engine fan ) , not enough air will make high side pressures very high.

Given the low side is at 40 and you have cold air in the car, I'd say the expansion valve is working properly. A stuck expansion valve is really the only place to have a "blockage"