Correct A/C pressures?
 

The wife's 04 EX isn't blowing air as cold as it used to be. Is it usual to top-off the charge or is weighing in the charge better? If it is ok to top off the charge, do you primarily go by pressures or temperature? If this were the type of A/C I usually work on, and since it's R-134a, I would expect the low side pressure to be no less than 28Psig (32F) but with an ideal low side of 35-40 Psig and the high side should be 170-200 Psig or thereabouts. Am I in the ballpark? Since this is a TXV system, do you measure liquid subcooling?

Since posting yesterday I fixed the car by recovering the charge, pulling a vacuum, and weighing in the listed maximum of 19.4 oz. of refrigerant. Low side at idle was as I expected at about 40+, but I was surprised that the low side would go below freezing when I revved the engine. I suppose there's probably a freeze safety temperature switch in the evaporator. Anyway, problem solved, and it only took about an hour, once I borrowed a 134a manifold from one of the mechanics at work.