Where is reservoir for a/c compressor? Is this a cause of moldy smell, when a/c

Reservoir for a/c compressor? This doesn't exist. Your odor is from inside your plenum, where the evaporator core and heater core live, and where condensation and moisture is very common. Ensure your cabin air filter is clean, ensure your evaporator drain tube is not plugged and is allowing moisture to escape the plenum. Finally, you can buy chemicals to deodorize this area and kill the bacteria. But my recommendation after checking the above is to run your ventilation system without the air conditioning system running for a few minutes before shutting off the car every day. Find the setting, usually "vent" that runs the air without the air conditioning and ensure the re-circulation mode is turned OFF. This will help air out the system when stopping the car.