Pressure really doesn't tell you level of charge in your system.
The 1.8 AC system takes 23.6 oz of R 134a
Freon is an old term for R 12, a refrigerant rarely seen today in auto's and incredibly expensive when it is found.
Pressure on the low side will vary depending upon the ambient temperature and relative humidity in which you are operating.
with a 40% level of humidity, 80 degrees, your center vent should be putting out 50 degree air, the low side pressure should be 32 Psig and the high side will be 240 psig.
if it is 100 degrees, the low pressure will be 46 and the high 319 with a center vent output of 64 degrees.
If the humidity jumps to 80 percent that 100 degree pressure will be 62 on the low side and 381 on the high.
If you don't know what you are doing and don't know how much refrigerant is in the system there really isn't a proper number for all situations across the board, it varies greatly.
Proper diagnosis requires BOTH a high gauge and a low gauge and there are pages of diagnostic procedures to follow.
Modern AC is dangerous and under extremely high pressure. People can and do get hurt by doing stupid things to them. Really, I'm not a mechanic fan but this is best left to those who know what they are doing if you don't have the gauges, the knowledge or the special tools for pulling a vacuum and fixing the system correctly. Not to mention it is illegal to vent refrigerant to the atmosphere knowingly.
So you are sitting there with a cheap chinese gauge on your 16 oz can of 134a. That one can is over half the entire capacity of the system! Add too much and the problems will be as bad as, if not worse, than having too little. You can damage many pieces, most notably the compressor. That little can empowers people to do what they should NOT be empowered to do.
Hook up the can if you must, don't start the engine and open the valve. As a general rule of thumb, Does it read 50 psi? If not, you need some work done to the system. What? only someone experienced in ac can help you find out, most often for a fee.