I have a ’93 240 SW that was new to me last fall.
The air conditioning is working and blowing cold but if I would like the AC to blow colder if possible.

My question is, how do I check to see if the 134a refrigerant is fully charged. If after I check the 134a is not fully charged, how do I add refrigerant?

 

get yourself a basic cheapo gauge from the autopart store. Has to read at least in 5 psi measurements. make sure you measure the car after it has sat overnight or during your work day and before you start it. A full charge will be equalized on both sides and read around 75 psi for 75F. the pressure is very close to the ambient temperature between 60 and 90F degrees.

or try to find a thermometer. place it in the center vent. drive with the A/C on coldest setting and the fan on high. The thermometer should be around 40-45F degrees.

Its a bit harder to determine a full charge on a running engine with out both gauges

in my Kragen/O'reilys or autozone. I saw some different basic gauges to check the low side.

 

or if you wana spend a few extra bucks get a dual gauge setup with manifold.