Proper air conditioner operation is a MUST in central Texas! Every part of the system must work together in order for you to get that cool relief sitting on I-35. The A/C system is put under it's most stress sitting in stop and go traffic and like anything else, this takes its toll on everything from your blower motor, to your compressor and even the radiator and engine cooling system.
Checking the charge level of the refrigerant is done by attaching hoses with gauges to the service ports. By reading the high-side and the low-side pressures, I can determine if the system is malfunctioning or simply low on a charge.
The easiest way to find a small leak is to recover and recharge the system while adding an ultra-violet reactive dye. Drive it around for a week or two and at which time, free of charge, I'll run an ultra-violet light over the system to determine the source of the leak.
BUT, please beware of shops that will do a 'free A/C check'. I have found that more times than not, after the hoses are removed, the service valves don't seal properly creating a new leak. I always replace these valves with any A/C service saving us both time and money in the long run.