A/C does not blow air cooler than 70 degrees

The SUV has rear air and the air conditioning was blowing at about 70°. A mechanic has replaced the compressor three times, the evaporator dryer, orifice tube, condenser. Even tried a heavier fan clutch. After replacing these items The low pressure is still at 70 and the high-pressure gets up to 300. All 134 levels are correct. The mechanic also replaced the heater cores in the rear end the expansion valve in the rear. The mechanic is supposed to be a air conditioning specialist, but unfortunately he has given up he says there is nothing else he can do. Air condition still blows at about 70 degrees.