Hussmann Proto-Aire Installation Manual page 116

Supply. If 24 VDC is not present, replace the POWERLINK™ Power
Supply. If 24 VDC is present, go to Step B14.
Step B13 Check fuse on defrost relay board. Replace fuse if it is blown. If fuse is
good, measure the voltage present at the white connector on the defrost relay
board. Place the positive test lead of you meter (typically the red wire) on
the normally open (N.O.) contact of the defrost relay board connector. Place
the negative test lead of your meter (typically the black wire) on the
common (COM) contact of the defrost relay board connector. Your digital
meter should read +24 volts DC. If +24 volts DC is present, the
POWERLINK™ Device must be replaced. If +24 volts DC is not present,
verify that wiring is correct as compared with the supplied customized
wiring diagram.
Problem C: Pressure transducer is not reading properly.
The transducer cable is shielded and should not have the bare drain wire attached to
door panel liner. The mechanical ground connection is achieved through the
threaded fitting on the suction and/or discharge header.
Step C1 Use a service gauge to verify the actual pressure reading. If the pressure
reading of the gauge and the reading of the Hand-Held controller is more
than 2 psi, check the pressure transducer offset, which is available on the
electronic control.
Step C2 Verify that the transducer range is set properly. Select the pressure input
you are currently having problems with and observe the transducer range.
Suction transducers should be selected for a 200 psi range while discharge
transducers require a 500 psi range. If the range is not set properly, make
the programming change and reevaluate the transducer. If the range is set
properly, go to Step C3.
Step C3 Use a digital volt meter with the scale set for DC volts to measure the
excitation voltage and signal voltage of the transducer.
Step C4 If the excitation voltage is not within the limits set by the controller
manufacturer.
Step C5 If the pressure reading, as indicated by the above formula matches the
reading of the Hand-Held Device replace the transducer. If the pressure
reading, as indicated by the above formula does not match the reading of the
Hand-Held Device, replace the control board.
Step C6 Use a digital voltmeter to measure the control transformer secondary
voltage. With the scale of your meter set for AC volts, remove the power
plug connected to the Protocol™ control and place your test leads of the
Protocol™ Installation and
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Service Manual