SYMPTOM: The thermostat will only allow Heat
or Off in 2-pipe installations, even though chilled
water is available.
CAUSE: Faulty, improperly wired, or improperly
installed H2O changeover sensor.
REMEDY: Confirm proper wiring of the change-
over sensor (between R and H2O). Confirm
proper placement of the sensor (good mechanical
coupling for temperature transfer).
Test the changeover sensor as follows:
1. Remove power from the fan coil system.
2. Disconnect the wire between the sensor and
the H2O terminal.
3. Place an ohmmeter between R and the wire
just disconnected from the sensor.
4. A good sensor will show continuity whenever
the water temperature is confirmed to be at or
below 65 degrees. If the sensor is open when
the water temperature is confirmed to be at or
below 65, replace the sensor.
TROUBLESHOOTING
Page 13
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