McQuay MicroTech II Installation And Maintenance

IM710 49
If 24 VAC supply reads low and/or the MCB is malfunc-
tioning, the sensor may be drawing too much current
(the 24 VAC terminals can only supply 30 mA). Discon-
nect sensor and recheck voltage and the MCB operation.
3. Using an accurate manometer or gauge, measure the
same pressure that the suspect transducer is sensing. To
do this, tap into the transducer high and low pressure
tubing or locate the measurement device taps next to the
transducer taps.
Note: If the suspect sensor is measuring duct static pres-
sure, verify that the high and low pressure taps have
been properly installed. An improper pressure tap
installation can cause severe fluctuations in the
sensed pressure. Refer to the model-specific instal-
lation manual for pressure tap installation guide-
lines (refer to Table 2 on page 3).
4. Measure the DC voltage output from the transducer.
a. If the sensor is SPS1 or SPS2 (duct static), measure
the voltage across the sensor “+” and “-” terminals.
b. If the sensor is SPS2 (building static), measure the
voltage across the “OT2” and “CM2” terminals on
the SPS2 terminal block.
If the measured voltage and pressure do not match, there
may be a wiring problem or the transducer may be
defective. Check the transducer input circuit wiring and
connections for defects.
If the measured voltage and pressure match, the MCB is
likely mis configured or defective.
5. Remove power from the controller by opening system
switch S1. If available, swap a similar good transducer
with the suspect transducer or try installing a new trans-
ducer. Restore power by closing S1, and verify whether
the suspect transducer is defective.
Figure 24: Duct Static Pressure Transducer Voltage vs.
Pressure
Figure 25: Building (Space) Static Pressure
Transducer Voltage vs. Pressure
CAUTION
The fittings on the pressure transducers are
fragile. Splice a tee fitting into each tap tube
instead of removing each tap tube from its
transducer fitting. Use an airtight cap to
cover the test port after the pressure mea-
surement.
Static Pressure ("W.C.)
1 2 3 4
Sensor Output (VDC)
1
2
3
4
5
Static Pressure ("W.C.)
Sensor Output (VDC)
1
2
3
4
5
-0.25 -0.125 0.000 0.125 0.25

McQuay MicroTech II Specifications

General

Brand	McQuay
Model	MicroTech II
Category	Controller
Language	English