Vacuum the Frigidaire microwave louver with the brush attachment to pull out as much dirt and debris as you can. (Ref 2)
Fill a spray bottle full of white vinegar. Dampen the cloth with warm water from the sink.
Spray the vinegar onto the cloth until it's wet. Wring it out slightly. Wipe down the louver on the Frigidaire microwave with the cloth.
Press the cloth into the slits in the louver to get off any grease of other buildup in the vents. Wipe them down until the greasy buildup is gone.
Rinse the cloth off with water and wipe down the louver again to remove any vinegar residue.