Lower the bed and extruder temps in Slic3r. It is best to start a separate Slic3r profile. (i.e. ABS profile, PLA profile). Most users on here have MULTIPLE profiles in Slic3r. Doing that makes it much easier to print in different materials with little down time and saves you favorite settings.
You "CAN" print PLA without a fan. But remember PLA doesn't cool as fast as ABS. So the layer last extruded needs to cool before then next is extruded. There are many fully printable options for you if you wanted to add a fan. If not, you would basically need a desk fan and either leave the SD4 door open for airflow, or remove the case altogether for said fan airflow.
SD4 is just a SD3 with a flashy case and a couple minor changes. PLA can be a lot of fun, but remember you need a cooling plan before you get any good results....solidoodle should specify it is "optional" to print PLA.
Just remember- myself and a few other users experienced excessive clogs when printing PLA, causing us to wise up and get an E3D...which you have to try pretty hard to clog