Maytag MTB1893ARS Operations Instructions download pdf (Page 9)

Component Testing

WARNING

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 Test Procedures

Evaporator The low pressure in the evaporator

allows liquid refrigerant exiting the

capillary to expand into a gas.

Expansion cools evaporator coil

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.

Test for leaks in evaporator with electronic leak detector or with soap solution.

Compressor oil is circulated with refrigerant; check for the presence of 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.

Evaporator heater

(defrost)

Activated when defrost thermostat,

defrost timer, and freezer control

complete circuit through heater.

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.

Thermostat

(defrost)

Thermostat is in a series circuit with

terminal 2 of defrost timer, and defrost

heater.

Controls the circuit from freezer

thermostat through defrost terminator to

defrost heater. Opens and breaks circuit

when thermostat senses preset high

temperature.

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 timer

cycles and refrigerator starts cooling again. Defrost thermostat senses a preset

low temperature and resets (closes).

WARNING

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.

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Maytag MTB1893ARS Operations Instructions Page 9

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