Fisher & Paykel RX256DT4X1 FP Service Manual page 31

Component
Evaporator Inner volume of evaporator
allows liquid refrigerant
discharged from capillary to
expand into refrigerant gas.
Expansion cools evaporator
tube and fin temperature to
approximately –20
transferring heat from freezer
section to refrigerant.
Passing through suction line to
compressor, the refrigerant
picks up superheat (a
relationship between pressure
and temperature that assures
complete vaporization of liquid
refrigerant) as the result of
capillary tube soldered to
suction line.
Refrigerant gas is pulled
through suction line by
compressor, completing
refrigeration cycle.
Evaporator defrost Activated when defrost
heater thermostat, defrost timer, and
freezer control complete circuit
through heater.
Thermostat Thermostat is in a series circuit
with terminal 2 of defrost timer,
and defrost heater. Circuit is
complete if evaporator fan motor
operates when cold.
Controls the circuit from freezer
thermostat through defrost
terminator to defrost heater.
Opens and breaks circuit when
thermostat senses preset high
temperature.
Thermistor Temperature sensing device.
Ice & water Customer water and ice
dispensing board dispensing interface board.
Electronic control Customer fresh food
board compartment and freezer
temperature adjustment
interface board.
Description
O
F,
Test Procedures
Test for leaks in evaporator with electronic leak detector or
with leak detection fluid.
Compressor oil is circulated with refrigerant; check for oil when
checking for leaks.
For minute leaks
1. Separate evaporator from rest of refrigeration system and
pressurize evaporator up to a maximum of 140 PSI with a
refrigerant and dry nitrogen combination.
2. Recheck for leaks.
To avoid personal injury or death from sudden eruption of
high pressure gases, observe the following:
Protect against a sudden eruption if high pressures are
required for leak checking.
Do not use high pressure compressed gases in
refrigeration systems without a reliable pressure
regulator and pressure relief valve in the lines.
Check resistance across heater.
To check defrost system:
1. Thermocouple defrost thermostat and plug refrigerator into
wattmeter.
2. Turn into Forced Defrost Mode. Wattmeter should read
specified watts (according to Technical Data Sheet).
3. When defrost thermostat reaches specified temperature
O
±5 F (see Technical Data Sheet), thermostat should
interrupt power to heater.
Test continuity across terminals.
With power off and evaporator coil below freezing, thermostat
should show continuity when checked with ohmmeter. See
"Heater, evaporator (defrost)" section for additional tests.
After defrost thermostat opens, thermostat remains open until
end of defrost cycle and refrigerator starts cooling again.
Defrost thermostat senses a preset low temperature and
resets (closes).
Check resistance across leads.
Temperature Resistance
O O
77 F / 25 C 10,000 ohms
O O
36 F / 2 C 29,500 ohms
O O
0 F / -18 C 86,300 ohms
Refer to specific the Technical Data Sheet supplied with the
unit for troubleshooting procedures.
Refer to specific the Technical Data Sheet supplied with the
unit for troubleshooting procedures.
31
WARNING
321023