Carrier 69NT40-541-505, Operation And Service Manual, Page: 117 / 143

7–25 T-368
7.21.3 Sensor Re-Installation
a. Sensors RTS/RRS
To properly position a return sensor, the sensor must
be fully inserted into the probe holder. This positioning
will give the sensor the optimum amount of exposure to
the return air stream, and will allow the Controller to
operate correctly. Insufficient probe insertion into the
probe holder will result in poor temperature control due
to the lack of air flow over the sensor.
It is also necessary to ensure that the probe tip does
not contact the evaporator back panel. The design min-
imum clearance of 6mm (1/4 inch) should be main-
tained (see
Figure 7.28 ).
b. Sensor STS/SRS
Reinstall the supply sensor as shown in Figure 7.29 .
For proper placement of the supply sensor, be sure to
position the seal section of the sensor against the side
of the mounting clamp.
c. Sensor DTS
The DTS sensor must have insulating material placed
completely over the sensor to insure the coil metal tem-
perature is sensed.
Figure 7.28 Return Sensor Positioning
Figure 7.29 Supply Sensor Positioning
7.22 VENT POSITION SENSOR (VPS)
The vent position sensor (VPS) determines the position
of the fresh air vent in near real-time via the Cd45.
The fresh air VPS alarm (AL50) will occur if the sensor
reading is not stable for five minutes or if the sensor is
outside of its valid range (shorted or open). This can
occur if the vent is loose or the panel is defective. To
confirm a defective panel, assure that the wing nut is
secure and then power cycle the unit.
The alarm should immediately go inactive. Check the
four-minute stability requirement. If the alarm reoccurs
after the four minutes and the panel was known to have
been stable, then the panel should be replaced.
If the alarm immediately reappears as active, the panel
should be replaced.
VPS:
In order to replace the VPS, the panel must be
removed and replaced with another upper fresh air
panel equipped with VPS.
Upon installation, a new VPS assembly requires cali-
bration as follows:
1. Rotate the vent to the 0CMH/CFM position.
2. Code select Cd45 will automatically be displayed.
Press the Enter key and hold for five seconds.
3. After the enter key has been pressed, the dis-
play will read CAL (for calibration).
4. Press the ALT MODE key and hold for five seconds.
5. After the calibration has been completed, Cd45
will display 0 CMH / CFM.
Cap and Grommet
Assembly
Probe
Holder
Return Sensor
Sensor
Wires
Return
Air
Stream
Evaporator
Back Panel
6 mm
(1/4 inch)
Evaporator Grille
Combination
Sensor (Mount in
Either Clamp)
Mounting
Clamp
Seal
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