Step 1: Pop off the air cleaner door - and slide out the plastic inner housing (filter assembly).
Step 2: Lay the assembly on the floor with the black pleat spacers facing up. Gently pop out the plastic pleat spacers from of the sides of the housing by lifing straight up. This may take some strength, but they DO come off. Set spacers to the side, do NOT throw these away, you can use them over and over again.
Step 3: Press in the tabs located on the sides of the housing (located on each end of the housing) .There are two tabs on each side - 4 total.
Step 4: Pull back the short side of the frame, and let the flaps lay flat on the floor. Repeat for the other end of the housing.
Step 5: Unsnap the lip running long-ways down the filter housing on both sides that folds over the cardboard edges of the filter media. Pull out the dirty filter and discard.
Step 6: All four sides of the plastic frame can fold down. Fold down the 2 short sides in preparation for the new filter as stated in step 4
Step 7: Place the new filter into the housing with the cardboard strips facing up.
Step 8: Line the small slit in the cardboard up with the lip on the side of the housing and place the cardboard in the lip.
Step 9: Re-snap the side of the housing clamping the filter to the side of the housing
Step 10: Fold up both sort ends of the housing - the tabs from step 3 will re-engage and snap in place.
Step 11: Place the pleat spacers (combs) into the filter making sure that the pleats are seperated by the fingers in the spacer. There is one finger for each pleat.
Step 12: Group the spacers closer together to make it easier to insert them.
Step 14: Firmly press down on the end of the spacer, snapping it in place.
Step 15: Repeat Step 14 for all of the spacers.
Step 16: Look for the ridge at the top and bottom of the metal Aprilaire housing unit.
Step 17: Line the metal ridge up with the canal in the plastic housing on top and bottom. Make sure airflow arrows on metal cabinet and on plastic housing face the same direction.
Step 18: Slide the plastic housing back into the metal cabinet.
Step 19: Snap the metal housing door back into place. There are four tabs that simply push into catches on the housing fame.
Step 20: You are DONE!!