Thermistors; Thermistor Failure; Reed Switch; Refrigeration System Diagnosis Guide - U-Line U-3090WCWCOL-00 Service Manual

Troubleshooting

Thermistors

Thermistors are used for various temperature readings. Thermistors
provide reliable temperature readings using a resistance which varies
based on surrounding temperatures. If a faulty thermistor is
suspected it may be tested using an accurate ohmmeter. In an ice
water (0°C / 32°F) resistance should measure 16.1 kilohms,

Thermistor Failure

Zone Thermistors
If a zone thermistor fails, the unit will continue to operate the
zone on a preset time interval of 10 minutes on and 30 minutes
off. The unit will otherwise operate normally. The error will be
displayed on the main display and "Self Test" and logged in "All
Errors".
Evaporator Thermistors
If an evaporator thermistor fails, the unit will rely on a preset
defrost timer during defrost cycles. The unit will otherwise
operate normally. Evaporator thermistor errors are hidden from
the display and recorded in "All Errors" and displayed in "Self
Test" modes.
Ambient Thermistor
The ambient thermistor is mainly used for diagnostics. If the
thermistor fails, the unit will operate normally.

Refrigeration System Diagnosis Guide

System Suction
Condition Pressure
Normal Normal
Higher than
Overcharge
normal
Lower than
Undercharge
normal
Somewhat lower
Partial
than normal -
Restriction
in vacuum
Complete In deep
Restriction vacuum
0 PSIG (0 bar)
No Gas to 25" (63.5 cm)
vacuum
28
Suction Compressor
Line Discharge
Slightly below
room Very hot
temperature
Very cold - Slightly warm to
may frost heavily hot
Warm -
near room Hot
temperature
Warm -
near room Very hot
temperature
Room Room
temperature temperature
(cool) (cool)
Room
temperature Cool to hot
(cool)
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Reed Switch

A reed switch is used to monitor door state. The switch side for each
zone is mounted under the cabinet and the magnet is mounted to the
cable arm of each respective door. When the door is closed magnetic
force pulls the reed to its contact and closes the circuit which turns
the light and display off. When the door is open the reed pulls away
from the contact and opens the circuit. If the door(s) are left open
for longer than 5 minutes, the switch will trigger an error code and
set an audible warning.
Magnet Away From Switch
(Door Open)
(Switch Open)
Condenser Capillary
Tube
Very hot Warm
Hot to warm Cool
Warm Warm
Top passes warm
lower passes cool Room
(near room temperature
temperature due (cool) or colder
to liquid
Room Room
temperature temperature
(cool) (cool)
Room Room
temperature temperature
(cool) (cool)
Magnet Close To Switch
(Door Closed)
(Switch Closed)
Evaporator Wattage
Cold Normal
Higher than
Cold
normal
Extremely cold
near inlet - outlet Lower than
below room normal
temperature
Extremely cold
near inlet -outlet
Lower than
below room
normal
temperature
backing up
Lower than
No refrigeration
normal
Lower than
No refrigeration
normal