48 IM710
Troubleshooting Communications Cards
BACnet Ethernet Card
For a detailed description and troubleshooting information
regarding the BACnet Ethernet communications card, refer
to installation and maintenance bulletin IM 703, MicroTech
II BACnet/Ethernet Communications Module. For details
regarding BACnet protocol data, refer to engineering data
document, ED 15 061, MicroTech II Protocol Information
Data for Vertical Self-contained Units.
BACnet MSTP Card
For a detailed description and troubleshooting information
regarding the BACnet MSTP communications card, refer to
installation and maintenance bulletin IM 704, MicroTech II
BACnet/MSTP Communications Module. For details regard-
ing BACnet protocol data, refer to engineering data docu-
ment, ED 15 061, MicroTech II Protocol Information Data
for Vertical Self-contained Units.
LonMark Cards
For a detailed description and troubleshooting information
regarding LonMark communications cards, refer to installa-
tion and maintenance bulletin IM 702, MicroTech II Lon-
Mark Communications Module. For details regarding
LonMark protocol data, refer to engineering data document,
ED 15 061, MicroTech II Protocol Information Data for Ver-
tical Self-contained Units.
Troubleshooting Static Pressure Trans-
ducers
The following procedure can be used to troubleshoot a sus-
pect sensor:
1. If the duct static pressure always reads 0 “WC on the
unit keypad/display and the discharge inlet vane posi-
tion or VFD speed is continuously ramping to 100%,
check the following:
a. If the unit has two duct static pressure sensors
(SPS1 and SPS2), verify that they both function
properly following steps 2 through 5 below. Also
check for faulty wiring connections at analog inputs
MCB-AI13 and MCB-AI14. The controller dis-
plays and controls to the lower of the two readings.
If a one is defective and inputs 0 volts to the con-
troller, the static pressure reading on the key-
pad/display reads 0 and the controller attempts to
increase the 0 value to setpoint by ramping up the
discharge inlet vanes or VFD.
b. If a second sensor (SPS2) is not installed or the
pressure tubing to it is not connected, make sure the
2nd P Sensor= parameter in the Unit Configuration
menu of the keypad/display is set to “None” so that
the controller ignores the second static pressure
analog input MCB-AI14.
c. If a second sensor (SPS2) is installed, but it is a
building space rather than a duct static pressure sen-
sor, make sure the 2nd P Sensor= parameter in the
Unit Configuration menu of the keypad/display is
set to “Bldg”.
2. Verify the 24 VAC power supply to the sensor.
a. If the sensor is SPS1 or SPS2 (duct static), verify
that there is 24 VAC between the suspect transducer
“+” and “-” terminals.
b. If the sensor is SPS2 (building static) verify that
there is 24 VAC between the “IN” and “CM2” ter-
minals on the SPS2 terminal block.
Table 26: MicroTech II Temperature Sensor -
Temperature vs. Resistance Chart
Temperature °F (°C) Resistance in Ohms
-40 (-40)
613
-31 (-35)
640
-22 (-30)
668
-13 (-25)
697
-4 (-20)
727
5 (-15)
758
14 (-10)
789
23 (-5)
822
32 (0)
855
41 (5)
889
50 (10)
924
59 (15)
960
68 (20)
997
77 (25)
1035
86 (30)
1074
95 (35)
1113
104 (40)
1153
113 (45)
1195
122 (50)
1237
131(55)
1279
140 (60)
1323
149 (65)
1368
158 (70)
1413
167 (75)
1459
176 (80)
1506
185 (85)
1554
194 (90)
1602
203 (95)
1652
212 (100)
1702
221(105)
1753
230(110)
1804
239 (115)
1856
248 (120)
1908
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