Pressure Transducers; Chilled Water Flow Switch - Carrier AQUASNAP 30RAP010-150 Start Up & Operation Manual

value read by the control in the Temperatures mode using the
scrolling marquee display.
Pressure Transducers —
transducers are different part numbers and can be distinguished
by the color of the transducer body, suction (yellow) and dis-
charge (red). No pressure transducer calibration is required.
The transducers operate on a 5 vdc supply, which is generated
by the main base board (MBB). See Fig. 38 for transducer con-
nections to the J8 connector on the MBB.
TROUBLESHOOTING — If a transducer is suspected of be-
ing faulty, first check supply voltage to the transducer. Supply
voltage should be 5 vdc ± 0.2 v. If supply voltage is correct,
compare pressure reading displayed on the scrolling marquee
display module against pressure shown on a calibrated pressure
gauge. Pressure readings should be within ± 15 psig. If the two
readings are not reasonably close, replace the pressure trans-
ducer.
Chilled Water Flow Switch —
flow switch is installed in the leaving fluid piping for all units
without the factory-installed hydronic package. See Fig. 39 and
40. Units with the optional hydronic package have the flow
switch installed in the entering fluid piping. This is a thermal-
dispersion flow switch with no field adjustments. The switch is
set for approximately 0.5 ft/sec of flow. The sensor tip houses
two thermistors and a heater element. One thermistor is located
in the sensor tip, closest to the flowing fluid. This thermistor is
used to detect changes in the flow velocity of the liquid. The
second thermistor is bonded to the cylindrical wall and is af-
fected only by changes in the temperature of the liquid. The
thermistors are positioned to be in close contact with the wall
of the sensor probe and, at the same time, to be kept separated
from each other within the confines of the probe.
In order to sense flow, it is necessary to heat one of the
thermistors in the probe. When power is applied, the tip of the
probe is heated. As the fluid starts to flow, heat will be carried
away from the sensor tip. Cooling of the first thermistor is a
function of how fast heat is conducted away by the flowing
liquid.
The difference in temperature between the two thermistors
provides a measurement of fluid velocity past the sensor probe.
When fluid velocity is high, more heat will be carried away
from the heated thermistor and the temperature differential will
be small. As fluid velocity decreases, less heat will be taken
from the heated thermistor and there will be an increase in tem-
perature differential.
When unit flow rate is above the minimum flow rate, then
the output is switched on, sending 24 vac to the MBB to prove
flow has been established.
For recommended maintenance, check the sensor tip for
build-up every 6 months. Clean the tip with a soft cloth. If
necessary, build-up (e.g., lime) can be removed with a common
vinegar cleansing agent.
5/8 in. HEX
The suction and discharge
A factory-installed
6" MINIMUM
CLEARANCE FOR
THERMISTOR
REMOVAL
Fig. 37 — Thermistor Well
1
1 RED
2
2
BLK
3
3 RED
4
4
BLK
5
5 BLU
6
6 BLU
1
7 RED
2
8
BLK
3
9
4
10
1
11 RED
2
12
BLK
J8
3
RED
13
4
14
BLK
1
15 RED
2
16
GRN
3
17 BLK
4
18 RED
5
19
GRN
6
BLK
20
7
21 RED
8
22 GRN
9
23 BLK
10
24 RED
11
25
GRN
12
26 BLK
LEGEND
ACCSY — Accessory
DPT — Discharge Pressure Transducer
LWT — Leaving Water Temperature Sensor
LVT — Low Voltage Terminal
OAT — Outdoor Air Temperature Sensor
RGT — Return Gas Temperature Sensor
SEN — Sensor Terminal Block
SPT — Space Temperature Sensor
Fig. 38 — Thermistor Connections to
Main Base Board, J8 Connector
4.2 in. (107 mm)
TORQUE WITH
WRENCH (SIZE 22 mm)
Fig. 39 — Chilled Water Flow Switch
1/4-18 NPT
54
RGTA
RGTB
LVT
J12 T55
3 23
4 22
OAT
SPACE TEMPERATURE
ACCESSORY OR
DUAL CHILLER LWT
EVAPORATOR ENTERING
FLUID TEMP
EVAPORATOR LEAVING
FLUID TEMP
B
+
C
DPTB
-
A
B
+
C
SPTB
-
A
B
+
C
DPTA
-
A
B
+
C
SPTA
-
A a30-4975
0.87 in.
(22 mm)
a30-5238
T-55
SEN
ACCSY
0.30 in.
(7.7 mm)