The kit that I bought has a gauge that gives the psi reading. When mine was blowing cold air, the reading was really high, like 110 psi. but I'm assuming that reading was when the compressor wasn't engaged.

You can only fill by weight after evacuating all existing "freon". It also is more or less a guide when talking about 15-20 year old cars.

100+ is entirely too high for low side. If that setup is making cool. I would bet on bad seals on the compressor and you are looking at 150 high 110 low. Not sure how it would evaporate to make cold in such a scenario but as I've mentioned low side only measuring is not very helpful for diagnosing AC problems.

The pressure will equalize hi to low when not running but 100+ is way higher than I've measured. Get a high/low reading