Evaporator; Defrost Heater; Defrost Thermostat - Maytag ATB1504ARQ Service Manual

Component Testing
To avoid risk of electrical shock, personal injury, or death, disconnect electrical power source to unit, unless test
procedures require power to be connected. Discharge capacitor through a resistor before attempting to service.
Ensure all ground wires are connected before certifying unit as repaired and/or operational.
Component Description

Evaporator

The low pressure in the evaporator
allows liquid refrigerant exiting the
capillary to expand into a gas.
Expansion cools evaporator tube and fin
temperature to approximately -20°F
transferring heat from freezer section to
refrigerant.
Passing through suction line back to the
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 circulated through the
suction line by compressor, completing
refrigeration cycle.
Evaporator heater Activated when defrost thermostat,
(defrost) defrost timer, and freezer control
complete circuit through heater.
Thermostat Thermostat is in a series circuit with
(defrost) 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.
©2003 Maytag Appliances Company
!
WARNING
Test Procedures
Test for leaks in evaporator with electronic leak detector or with soap solution.
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 severe personal injury or death from sudden erruption of
high pressurres 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 defrost mode. Wattmeter should read specified watts (according to
Technical Data Sheet).
3. When defrost thermostat reaches specified temperature ±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).
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!
WARNING
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