A friend of mine found this device in the corner of the ceiling in the living room of his recently purchased house. The previous owner has no idea what it was.

One of the KDU connectors goes into the roof and the CON3 cable was just hanging loose inside the box.

Given the SPEED, PUMP and DUMP LEDs, we suspect it has something to do with air conditioning but we're not sure.

Any ideas would be most welcome.

enter image description here

  • Any markings/labels on the outside or inside of the lid?
    – FreeMan
    Apr 19 '21 at 12:56
  • I tried searches for AGA BMC 5.0 (as found in the lower left corner of the board) and came up with nothing helpful. Most things were either about "gas", "AGA" brand gas grills, birth weight or "baseboard management controllers" on mother boards. An image search for salinity aga bmc 5.0 (based on the thought that this may a water treatment controller of sorts) turned up a bunch of things, but work blocks a lot of images, so I'll leave looking through them as an exercise for the OP.
    – FreeMan
    Apr 19 '21 at 13:03
  • 1
    It also looks like there may be additional identifying marks under the white pads in the top right corner. Those are there for insulating contacts from the metal housing of the 9v batter that's supposed to be installed, but lifting them may reveal something useful.
    – FreeMan
    Apr 19 '21 at 13:06
  • Where is the cable going? It looks like power but has extra wires but I agree with the guess of something to do with water+
    – Ed Beal
    Apr 19 '21 at 14:06
  • @FreeMan Looks as if there might be a serial number or type-number under those white pads.
    – Tonny
    Apr 19 '21 at 14:20

My best guess is a controller unit for a HVAC system with an (optional) humidifier.
AGA is a well-known manufacturer of heating systems and ovens, but they used to make HVAC systems as well in the past.
The salinity sensor solder-pads (unused on this PCB) lead me to the humidifier part guess. (Salinity only makes sense of you have a connected water-supply somewhere.)
The KDU (Keyboard Display Unit ?) connectors most likely were hookups to a controlling keypad/thermostat.
The wires on the bottom-left probably go to the actual HVAC unit in the attic. (Or go were that unit used to be.) And this controller would get its operating power from the HVAC via those wires as well.
Having a 9V battery clip inside such a unit wouldn't be unusual either. Typically so it retains its settings during a power-cut.


I believe this is for an evaporative cooler, also known as a swamp cooler. Evaporative coolers only work in hot, dry climates -- given that Perth is in Western Australia I suspect this house would qualify. (I also found a few installers in Perth to confirm this: one, two, three.)

Then I found a few different evaporative cooler manuals which mention some of the things indicated on that control board -- here's one example, from a Seeley International manual:

  • "The WaterManager™ allows you to specify either high or low salinity settings."
  • "Manual mode will allow you to change settings for operating the cooler, such as altering fan speeds, pump control and manual drain control."

This fits given the controller settings, the geographic location, and the location of the wire running to the roof. It's possible that a newer cooler was installed and this controller was abandoned in place. The large IC with the red sticker looks like an old through-hole ASIC. A newer controller would probably use an SMD, and likely wouldn't have the functions in this board in a separate enclosure from the display or keypad.

  • It is an swamp cooler or evaporative cooler controller and it holds the battery for the control panel. Also if you look under the battery cushion I believe the model info is there. Jul 9 '21 at 1:33

With the salinity connection bottom right I suggest it is a water treatment controller.

  • This answer was flagged as low-quality because of its length and content. You may want to flesh it out some...
    – FreeMan
    Apr 19 '21 at 11:56
  • @FreeMan are you saying it is incorrect? what would you suggest?
    – Solar Mike
    Apr 19 '21 at 12:11
  • Nope, just that the system (or someone) flagged it. Can't argue against your answer (or for it, for that matter), just letting you know. In general the short, single sentence answers get flagged, but, sometimes, that's all that's really needed...
    – FreeMan
    Apr 19 '21 at 12:12
  • In terms of expanding on this answer, it does seem like some explanation as to why, in spite of the location (ceiling) and route of connections (to the roof), you still believe this would be related to water treatment. Water treatment systems aren't typically found on the roof. Apr 19 '21 at 21:25

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