RT-SVD03L-EN
167
Figure 104.
Transducer voltage output vs. pressure
Transducer Voltage Output vs Pressure Input
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
-0. 5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
Pressure (inches w.c.)
V
o
lt
s
The transducer has a 0 to 5VDC range with a 0.25 to
2.125 VDC valid output range. The output is
proportional. The chart illustrates the measured output
voltage at typical supply duct pressures.
VHR Relay
When the unit transitions from occupied mode to
morning warm-up, daytime warm-up or unoccupied
mode, the VHR relay is energized, as long as the unit
has a valid zone temperature input at RTRM J6 1&2, or
through a BAYSENS020* zone sensor.
Figure 105.
VHR relay
5
3
4
VHR
LTB - 3
The VHR relay has a set of contacts on TB3 for the
purpose of commanding the VAV boxes to drive open
to maximum airflow position.
If the unit has heat, the VAV boxes must be driven
open. If the boxes are allowed to stay in control, the
boxes may try to close instead of open when the warm
air enters the room.
•
When RTAM DIP SW1-1 is on, the output voltage
range is approximately 0 to 10.5VDC.
•
When RTAM DIP SW1-1 is off, the output voltage
range is approximately 2.5 to 8.5VDC.
•
IGV: When the supply fan is on and the output is
0%, the IGV are closed.
•
VFD: When the supply fan is on and the output is
0%, the VFD runs at 35hz.
•
If the supply static pressure goes below -0.2"
(0.2VDC) the IGV / VFD output will stay at 0% and
the diagnostic COOL FAIL + SERVICE FAIL will be
present.
•
If the static pressure exceeds 3.8" WC the supply
fan will stop and the diagnostic HEAT FAIL + COOL
FAIL +SERVICE FAIL will be present.
•
During the heating modes; Daytime Warm-up,
Morning Warm-up, and Unoccupied, the IGV or VFD
output is always 100%.
Troubleshooting Tips
If the transducer output voltages do not seem right,
connect a 0-5" manometer in parallel with the
transducer. This way you can see the same pressure
the transducer is seeing. Many transducers get
replaced in error when the real culprit is a loose tube or
clogged fitting.
The polyethylene tubing in the transducer circuit does
not readily go back to its original shape after use.
Therefore, if a tube is removed from a fitting it should
be cut back to a fresh end prior to reattaching.
Measure the transducer output voltage at RTAM
terminal J1-3 to chassis ground.
When the supply fan is off, the transducer output
voltage should be approximately 0.25VDC. If the
voltage output is high or low, unplug the transducer
tubing to see if the voltage increases or decreases. If it
does, a tube is probably clogged.
The input voltage to the transducer is measured
between RTAM J1-4 and chassis ground. It should be
5VDC. If it is low, unplug the transducer and measure
the voltage again. If OK now, the transducer or
transducer wiring is shorted to common or ground.
The outdoor air pressure sensor must be mounted as
shown in
. If the sensor is mounted
upside down the tubing can fill with water during
heavy rains.
The static pressure sensing cover plate in the fan
section of the unit is bolted to the fan bulkhead. The
bulkhead has a very small (0.07") hole in the center
area. The purpose of using such a small hole is to
ensure that the transducer only sees the average
supply air pressure. If the hole is enlarged, the
transducer could respond erratically. If the hole is
plugged, the transducer will not respond. If the gasket
between the cover plate and bulkhead is leaking, the
supply pressure will appear to be abnormally low since
the cover plate is in the fan section.
Application Notes
Some applications call for relocating the supply air
tube to 2/3 of the way down the duct. If this is done, be
certain that there is no potential obstruction between
the unit and the pickup point (such as fire dampers). A
separate high duct static switch may need to be added.
The outside air pressure sensor should be located on
top of the unit as shown in
. Some
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