Wow, this is an oldie, but I guess I subscribed! The thing that troubles me about your low side pressure is this; it is fine *if* it were with the compressor running and yours hasn't for some time I am guessing. You see, when your compressor is off, the high side pressure and the low side pressure will equalize somewhere in the middle. Let's say that your AC is running properly, your low side of 35# is about right and your hide side using the other posters suggestion of say 100 degrees plus ambient temperature is in the ballpark. So, with unit running you might have 35-175 (low & high). When unit is nopt running for any number of hours, pressures will bleed into one another and your "mixed" pressure may be 70#. The fact that it drops to 35# is proof the compressor is working as it takes low side pressure and compresses it into high side of say 170. You have 35 on low and I bet you have 35# on high side as well if compressor has not run in a while.
See where I am going? Check both low and high with car off since compressor is not running and both should read the same and should be well over 35#. I do not subscribe to "just add more" but I am letting you draw your own conclusion. If you have an equalized 35# with no compressor action, what do you think high and low side would do
*if* compressor could kick in?