Replace Fan in APC Back-UPS XS 900 (BX900R)

Mark Berry December 16, 2015

The Young Lin DFB401024H fan that comes in the Back-UPS XS 900 VA (BX900R) uninterruptible power supply is rated for 50,000 hours or 5.7 years. At some point the bearings will fail and it will start screeching. Here’s how I replaced the fan.

The first challenge is finding an equivalent 24-volt brushless fan. Last time I replaced one of these, I used an Orion OD4010-24HB fan, sourced from Digi-Key. They are out of stock on that one. This time, I used an Orion OD4010-24MB, which has Air Flow of 6.0 CFM vs. the 7.0 CFM of the OD4010-24HB, but still has ball bearings (longer life than sealed sleeve OD4010-24HSS). The original Young Lin DFB401024H had air flow of 6.4 CFM, so pretty close.

This YouTube video has some helpful information but I wanted to document the actual disassembly and replacement steps. Use these instructions at your own risk!

  1. Remove the UPS battery.
  2. Remove back of UPS (four screws).
  3. Remove two screws inside battery compartment. Note that one goes through black wire connector.
  4. Pry off front cover with a screwdriver. Remove three screws under front cover.
  5. Place unit on left side (as viewed from front). Lift off right side. There is a loose black plastic thing covering the yellow transformer. If it falls off, just set it back on the transformer.
  6. Temporarily attach battery and check air flow direction. (I forgot this this time!)
  7. Lift out circuit board. Unplug fan from circuit board. Unscrew fan from front of fan.
  8. Attach new fan. I used crimp-on phone splice connectors to connect new fan to old two-print plug.
  9. Screws were too short because new fan did not have recessed screw holes. Use a 13/64 drill bit to create recess in new fan screw holes.
  10. Screw in fan. Plug into circuit board. Temporarily attach battery to test fan. Air flow is front-to-back; I think that’s right, since it means it goes directly to a heat sink, if that’s that is behind the fan mount, and eventually out the top of the unit.
  11. Reassemble everything. Be careful to get the front ribbon cable into its slot.

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