Installation and Maintenance Manual

Installation—Mechanical
38 UNT-SVX07D-EN
Automatic Changeover Sensor
Two-pipe changeover units with either the Tracer ZN010,
ZN510, ZN520, and UC400 and CSTI controls have an
automatic changeover sensor that determines heating or
cooling mode based on the supply water temperature. On
units with a factory piping package, the factory straps the
changeover sensor to the piping supply water pipe. See
Figure 5, p. 38 and Figure 6, p. 38.
If the unit does not have a factory piping package, the
factory attaches the sensor and coiled lead wires to the
piping side end panel. The installer should attach the
sensor parallel to and in direct contact with the supply
water pipe.
Note: The installer is responsible to ensure the
changeover sensor is installed in a location that can
sense active water temperature. Otherwise, the
unit may fail to sense the correct operating mode
and disable temperature control.
When using field supplied three-way valves, install the
changeover sensor upstream of the valve on the supply
water pipe. When using field supplied two-way control
valves, install the changeover sensor in a location that will
detect active water temperature. The unit must always be
able to sense the correct system water temperature,
regardless of the control valve position.
Note: The maximum length of the automatic changeover
wire cannot exceed ten feet from the control panel.
If the sensor extends beyond the unit chassis, use
shielded conductors to eliminate radio frequency
interference (RFI).
Venting the Hydronic Coil
The hydronic coil contains a vent, either manual or
automatic, to release air from the unit. This vent is not
sufficient for venting the water piping system in the
building.
The coil air vent is on the piping side, above the coil
connections on the unit. See Figure 7 and Figure 8.
Perform the following steps to vent the coil after installing
the unit.
1. Pressurize the building piping system with water and
vent any trapped air at system vents.
Figure 5. Attach the changeover sensor to the entering
water pipe as shown for changeover to work
properly
Figure 6. Close-up view of the changeover sensor
Figure 7. Manual coil air vent with set screw
Figure 8. Manual coil air vent with Shrader fitting
UNT-SVX07_-EN.book Page 38 Friday, April 27, 2012 9:40 AM