Carrier 19XL - Manual (Page 220)

Checking the Display Messages
The first area to check when troubleshooting the 19XL is the LID display. If the alarm light is
flashing, check the primary and secondary message lines on the LID default screen ( Figure 13 ).
These messages will indicate where the fault is occurring. The Alarm History table on the LID
Service menu will also carry an alarm message to further expand on this alarm. For a complete
listing of messages, see Table 10 . If the alarm light starts to flash while accessing a menu
screen, depress EXIT to return to the Default screen to read the failure message. The
compressor will not run with an alarm condition existing, unless the alarm type is an
unauthorized start or a failure to shut down.
Checking Temperature Sensors
All temperature sensors are of the thermistor type. This means that the resistance of the
sensor varies with temperature. All sensors have the same resistance characteristics.
Determine sensor temperature by measuring voltage drop if the controls are powered, or
resistance if the controls are powered off. Compare the readings to the values listed in Table
11A or Table 11B .
Resistance Check
Turn off the control power and disconnect the terminal plug of the sensor in question from the
module. Measure sensor resistance between receptacles designated by the wiring diagram with