Transducer Troubleshooting; Refrigerant Pressure Transducer Replacement And Calibration - Carrier 48FP Controls Operation And Troubleshooting

Fig. 40 — Thermistor T3 and T4 Locations, Size 054-104 Units; Header End of Coil (cont)
Transducer Troubleshooting —
system may use transducers to measure pressures around the
system. See Table 1 for pressure transducer locations and
Fig. 41 for typical refrigerant pressure transducer. If a transduc-
er is suspected of being faulty, check the voltage to the trans-
ducer. The refrigerant pressure transducer supply voltage
should be 5 vdc ± 0.2 v. These transducers convert the mea-
sured refrigerant pressure to a voltage. This voltage is then
evaluated as a ratio to the 5 vdc ± 0.2 v supply voltage. Read
the voltage on channel 12. If the check filter switch is open,
then 5 v is used for the ratio. If the supply voltage is correct,
compare the pressure reading displayed on the HSIO keypad
and the pressure obtained on a calibrated pressure gage.
NOTE: A 24-vac isolation transformer is required for proper
operation of each field-installed IAQ and humidity sensor. One
transformer is required for each sensor to avoid damage to
refrigerant pressure transducers.
IMPORTANT: Compressor service valves shut off
the pressure port when backseated. Be sure that
service valves with transducers installed on the pres-
sure port are not backseated to ensure proper trans-
ducer operation.
To check the refrigerant pressure transducers:
1. Use the pressure subfunction of the status function
( and ) to determine if the pressure
transducers are reading correctly. Connect a calibrated
gage to the lead compressor suction or discharge pres-
sure connection to check transducer reading.
088, 104
The unit control
80
2. Make sure that the transducer leads are properly con-
nected in the junction box and to the PSIO1. Check the
transformer TRAN4 output. Check the transducer sup-
ply voltage from PS1. It should be 5 vdc ± 0.2 v.
Check the supply voltage to PSIO channel 12.
Fig. 41 — Refrigerant Pressure Transducer
Refrigerant Pressure Transducer Replace-
ment and Calibration —
the compressor and allow them to be exposed to atmospheric
pressure. Refrigerant ports under transducers have Schrader-
type ports. Follow the steps in Table 61 to calibrate (zero) the
transducers.
After calibration, the results may be checked by following
the steps outlined in Table 62. Pressure readings other than
0.0 psig indicate that the calibration was unsuccessful. Repeat
the calibration procedure for any value that is greater than
± 1.0 psig.
After satisfactory calibration of the transducers, reinstall
them on the compressors.
Remove the transducers from