MaxxFan 7500K — Rear-Bay Install (2025 Sprinter)

Single rear fan. DIYvan rear adapter. DIY 3/4″ plywood interior frame. Through-bolted. No anti-crack ring.

Materials

Hardware

Tools

Cut, prep, seal

Cutting and drilling

Frame finishing

Acoustic package removal (inside roof)

Electrical

Placement

Layout and Cut (cut first)

  1. Mask a 16″×16″ area. Use adapter as template to mark a 14″×14″ square.
  2. Drill 1/8″ pilots at corners. Enlarge corners to ~3/8″.
  3. Set up the interior shavings catcher: taped plastic or a big box “hammock.” Add magnets near the cut line.
  4. Jigsaw the square. Support the slug to prevent panel distortion.
  5. Deburr and file smooth. Prime and paint all raw edges. Let cure.

Remove acoustic panels (inside)

  1. Warm sound-deadener with heat gun until pliable.
  2. Lift with plastic scraper. Expose flat painted steel where the wood frame will sit.
  3. Wipe residue with IPA or mild adhesive remover. Dry fully.

Build and finish the interior frame

  1. Cut 3/4″ birch ply to OD ~18″×18″ with 14″×14″ inner opening.
  2. Paint dark gray and seal all edges; let cure.
  3. Drill shallow counterbores (Forstner 1–1-1/4″) so a socket fits the nuts. Leave ≥1/2″ wood under each nut.

Bond the adapter (triangle bead)

  1. Clean roof and adapter with IPA. Mask edges.
  2. Cut the nozzle to a 45° wedge tip; run a 1/4″ triangular bead of polyurethane: full perimeter + two cross-ribs; keep bead ~1/8–3/16″ inboard from outer edge.
  3. Place adapter. Apply even pressure or light weights. Tool minimal squeeze-out. Pull tape while wet. Allow skin time per product data sheet.

Flange, through-bolting, and butyl

  1. Apply 1″×1/8″ butyl to the underside of the fan flange.
  2. Set flange on adapter. Align holes.
  3. Drill #10 clearance through the full stack (≈13/64″ / 5 mm).
  4. Insert bolts from outside with fender washers. Inside: fender washer + nyloc on the frame.
  5. Tighten in a cross pattern until butyl squeezes uniformly. Do not crush the flange.

Trim butyl squeeze-out

Lap sealant (topside cap)

  1. Mask around the flange and over each exterior head/washer.
  2. Apply self-leveling lap sealant: cover all heads/washers and run a continuous perimeter fillet.
  3. Pull tape immediately for clean lines. Let cure fully.
  4. Optional: if you still want a darker look and lack black lap, apply a thin cosmetic Flex Seal topcoat only after full cure. Do not rely on it as the primary seal.

Fan body and wiring

  1. Run 12 VDC with a 5 A fused feed. Observe polarity. Provide strain relief.
  2. Set the fan body on the roof flange. Fasten with the four kit screws only.
  3. Trim and install the interior garnish to cover the frame.

QA checklist

Maintenance