Transducer Troubleshooting; Forcing Inputs And Outputs - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

Transducer Troubleshooting

The electronic control uses suction pressure transducers to
measure the suction pressure of the refrigerant circuits. The
pressure/voltage characteristics of these transducers are in
shown in Table 24, the 5vdc power is applied to legs A and B
of the transducer and legs B to C represent the signal voltage.
To use the voltage drop table for troubleshooting, read the volt-
age across A and B, then subtract the voltage reading from B to
C. This is the voltage drop which can be looked up in Table 24.
The accuracy of these transducers can be verified by connect-
ing an accurate pressure gauge to the second refrigerant port in
the suction line.

Forcing Inputs and Outputs

Many variables may have their value forced through CCN or
directly at the local display. This can be useful during diagnos-
tic testing and also during operation, typically as part of an ad-
vanced third party control scheme. Input and output points that
may be forced are indicated as 'forcible' in the write status col-
umn of the display and CCN tables.
If the user needs to force a variable, follow the same process as
when editing a configuration parameter. A forced variable will
be displayed on the scrolling marquee with a blinking period "."
following its value. A forced value on Navigator accessory is in-
dicated with a blinking "f". A forced value on CCN devices is
indicated with "Control" if forced at the unit display, or "Super-
visor" if forced via CCN. To remove a local force with the
scrolling marquee, select the point with the ENTER key and then
press the up-arrow and down-arrow keys simultaneously.
NOTE: In the case of a control power reset, any force in effect at
the time of power reset will be cleared.
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