R134 systems don't get as 'ice cold' as the old R12 systems - however, the systems are designed to keep the cabin temperature comfortable.
My concern is that you said the system was empty. This can be a bad thing in that air could have entered the system. Air does not work well in the refrigeration cycle, particularly if it has enough moisture that will freeze. It appears that you have dodged this bullet, for now.
The proper way to refill an empty system would be to pull a vacuum on it. This ensures that all air is removed, and the low pressure causes most of the moisture to evaporate and to be pulled out, as water boils off at around 109degF, instead of its normal 212degF, near absolute vacuum.
The A/C label located somewhere in the engine compartment should list how much refrigerant is needed - typically on the order of 2-3 lbs. You've already added 18 oz, so need to add enough to make up the difference.
My concern is that you have a small leak - otherwise, the system should not have bled down. This will be something to monitor - the system has a low-pressure interlock that will not allow the compressor to run if the pressure gets too low - this feature both protects the compressor as well as prevents evaporator freezing.
Please be careful! A/C systems operate under high pressures and extreme temperatures - a mistake can cause equipment damage or personal injury that will likely cost much much more than the savings experienced by doing it yourself. Eye and hand protection should always be used.
