Issue
CZU with remote setpoint adjust DRT3451 / STR611 / STR612. FCU controller not controlling correctly.
Environment
CZU fan coil unit discrete controller.
Cause
Wiring difference of the older type DRT adjustable setpoint sensor and the newer type STR adjustable setpoint sensor to the CZU controller.
Resolution
DRT3451
If used as a sensor and setpoint unit then terminals A and C are used.
If used as a setpoint only with a separate sensor then terminals A and B are used with the temperature sensor in series.
STR611/612
If used as a sensor and setpoint unit then terminals 22 and 23 are used.
If used as a setpoint only with a separate sensor then terminals 22 and 24 are used with the temperature sensor in series.
CZU
For any of the sensors listed above, the sensor is wired to terminals 9 and 10 on the CZU.
If a remote setpoint adjust unit is used then the internal setpoint on the CZU controller needs to be disabled by setting the internal setpoint potentiometer to 10°C. The setpoint dial is shown in the centre of the diagram.
