I own a condo with two Islandaire EZ09EBMXH8N10AA PTACs, one of which is acting weird. They have self-contained A/C mechanisms, but the rooms are heated by pumping hot water from the building through the unit while a fan blows air across the radiator/heat sink.

A wiring harness comes out of each unit and connects the brain board to a SPST over-temperature switch clamped to the water pipe and a brain board-controlled valve on the water pipe. It's not clear which is the incoming and which is the return pipe.

My problem is that one PTAC will only run momentarily, and then the fan shuts off and the room won't stay heated.

Troubleshooting data so far:

  • Sometimes (20% of the time) the unit will run properly for several minutes (hot water flowing in, fan turning, room warming); most of the time the fan will kick on for 10 seconds or so, then turn off.
  • When the fan is not running but supposed to be, I'll periodically hear a 10-second-long buzzing, humming sound from inside the unit. I do not remember it doing this formerly, and the sound is something like the hum of a transformer, but more metallic/nasal.
  • When I switch the fan to manual mode, it starts up immediately and runs indefinitely every time, so it appears the motor start cap and the motor itself are good. There is no grinding or sputtering or other misbehavior.
  • If I power cycle the unit, I can hear the valve operate, and warm water does appear to flow into the unit every time.
  • I swapped the over-temperature switches and both PTACs behaved as if nothing had changed, so these switches appear to be fine.
  • The thermostat on the wall appears to be doing its job; it is showing the proper temperature and is indicating properly indicated when the heater should be on.

Any ideas?

  • I take it there's no power at the fan motor when the fan's not running but should be? – ThreePhaseEel Nov 3 '19 at 2:29

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