Humidi-Mizer Troubleshooting; Thermistor Troubleshooting; Transducer Troubleshooting - Carrier WeatherMaker 48A2020 Controls, Start-Up, Operation, Service And Troubleshooting Instructions

Humidi-MiZer Troubleshooting

Use the unit scrolling marquee or a CCN device to view the sta-
tus display and the diagnostic display for information concerning
cooling operation with the Humidi-MiZer system. Check the
Current Alarms and Alarm History for any unresolved alarm
codes and correct. Verify Humidi-MiZer configuration settings
are correct for the site requirements. If alarm conditions are cor-
rected and cleared, then operation of the compressors, fans, and
Humidi-MiZer valves may be verified by using the Service Test
mode. By attaching temperature probes across the 3-way valve,
verify the temperature profiles satisfy the corresponding mode
setting. See page 23 for Service Test information. In addition to
the Cooling Service Analysis (Table 78), see the Humidi-MiZer
Service Analysis (Table 79) for more information.

Thermistor Troubleshooting

See Tables 82-84 for temperature vs. resistance data.
When replacing thermistors SCT.A and SCT.B, reuse the origi-
nal hardware. These thermistors must be clamped tightly to the
hairpins of the condenser.
The EDT, OAT, RAT, LAT, SAT, T55, T56, and T58 space tem-
perature sensors use 10K thermistors. Resistances at various
temperatures are listed in Tables 85 and 86.
The 48/50A units with the optional variable capacity digital
compressor are equipped with a digital scroll discharge therm-
istor (DTT). The DTT is an 86K thermistor connected to RXB
at plug J6, terminals 3 and 4. The resistance values are listed in
Table 87.
THERMISTOR/TEMPERATURE SENSOR CHECK
A high quality digital volt-ohmmeter is required to perform
this check.
1. Connect the digital voltmeter across the appropriate thermis-
tor terminals at the J8 terminal strip on the main base board.
2. Using the voltage reading obtained, read the sensor tempera-
ture from Tables 82-87.
3. To check thermistor accuracy, measure temperature at
probe location with an accurate thermocouple-type tem-
perature-measuring instrument. Insulate thermocouple to
avoid ambient temperatures from influencing reading.
Temperature measured by thermocouple and temperature
determined from thermistor voltage reading should be
close, 5°F (3°C) if care was taken in applying thermocou-
ple and taking readings.
If a more accurate check is required, unit must be shut down
and thermistor removed and checked at a known temperature
(freezing point or boiling point of water) using either voltage
drop measured across thermistor at the J8 terminal, or by deter-
mining the resistance with unit shut down and thermistor dis-
connected from J8. Compare the values determined with the
value read by the control in the Temperatures mode using the
scrolling marquee display.

Transducer Troubleshooting

On 48/50A units, the electronic control uses 4 pressure transduc-
ers to measure the suction and discharge pressure of circuits A and
B. The pressure/voltage characteristics of these transducers are
shown in Tables 88 and 89. The accuracy of these transducers can
be verified by connecting an accurate pressure gage to the second
refrigerant port in the suction line.
84