Post #2 told you were the A/C pump is located. You can tell if the pump is spinning or not by looking at the pulley in the off and then on position while the engine is running. BE very careful you do not get anything dropped or tangled in the belt. You also need to read those other post again, because they all recommend using a set of accurate gauges. If you do not know how to read those gauges then simply buying a can of refrigerant and putting it into your system can lead to bigger problems; Penny wise pound foolish, but good luck and hope it works out good for you.

to answer your question above; The system always has pressure (if it has not all leaked out, and yours has not completely leaked out from what you say) with the pump running or not.