Maytag MTB1893ARS Operations Instructions download pdf (Page 24)

System Diagnosis

• Only partial frosting of evaporator instead of even

frosting of entire coil.

NOTE 1: Usually the first thing that is noticed by the

user is a rise in temperature of there fresh food.

Although temperatures will rise in both the

freezer section and the fresh food compartment,

the frozen meats and vegetables will not thaw

immediately. The customer doesn't associate

the problem with the freezer section and will first

notice that milk and other food beverages are

not cold enough.

Under some circumstances, a slight shortage of

refrigerant, might cause food in the fresh food

compartment to freeze due to the additional running

time. With a refrigerant leak, however, it always gets

worse and as the refrigerant charge decreases the

temperature will continue to rise.

With a shortage of refrigerant the capillary line will not

have a full column of liquid. As a result, there is a

noticeable hissing sound in the evaporator. This should

not be mistaken for the regular refrigerant boiling

sounds that would be considered normal.

Symptoms of a Restriction

Always remember refrigeration (cooling) occurs on the

low pressure side of a partial restriction (obviously a

total restriction will completely stop the circulation of

refrigerant and no cooling will take place).

Physically feel the refrigeration lines when a restriction

is suspected. The most common place for a restriction

is at the drier-filter or at the capillary tube inlet or outlet.

If the restriction is not total there will be a temperature

difference at the point of restriction, the area on the

evaporator side will be cooler. In many cases frost and/

or condensation will be present. A longer time is

required for the system to equalize.

Any kinked line will cause a restriction so the entire

system should be visually checked.

A slight restriction will give the same indications as a

refrigerant shortage with lower than normal back

pressure, head pressure, and wattage, warmer product

temperatures.

NOTE 2: If a total restriction is on the discharge side of

the compressor, higher than normal head

pressures and wattages would result. This is

true only while the low side is being pumped out

and if the restriction was between the

compressor and the first half of the condenser.

To diagnose for a restriction versus a refrigerant

shortage, discharge the system, replace the drier-filter,

evacuate and recharge with the specified refrigerant

charge. If the unit performs normally three possibilities

exist: 1) refrigerant loss, 2) partially restricted drier-

filter, and 3) moisture in system.

If the unit performs as it previously did you may have a

restricted capillary line or condenser or kinked line.

Find the point of restriction and correct it.

A restriction reduces the flow rate of the refrigerant and

consequently reduces the rate of heat removal.

Complete restriction may be caused by moisture, solid

contaminants in the system, or a poorly soldered joint.

Moisture freezes at the evaporator inlet end of the

capillary tube or solid contaminants collect in the drier-

filter. The wattage drops because the compressor is not

circulating the usual amount of refrigerant.

As far as pressure readings are concerned, if the

restriction, such as a kinked line or a joint soldered shut

is anywhere on the low side, the suction pressure would

probably be in a vacuum while the head pressure will be

near normal. If the restriction is on the high side, the

suction pressure, again, will probably be in a vacuum

while the head pressure will be higher than normal

during the pump out period described earlier. In either

case, it will take longer than the normal ten minutes or

so for the head pressure to equalize with the low side

after the compressor stops.

Symptoms of Air in System

This can result from a low side leak or improper

servicing. If a leak should occur on the low side, the

temperature control would not be satisfied; thus,

continuous running of the compressor would result. The

compressor would eventually pump the low side into a

vacuum drawing air and moisture into the system. Air

and R134A do not mix so the air pressure would be

added to the normal head pressure, resulting in higher

than normal head pressures.

One way to determine if air is in the system is to read

the head pressure gauge with the product off and

evaporator and condenser at the same temperature and

then take the temperature on the condenser outlet tube.

This temperature should be within 3° or 4° F. of what the

Pressure-Temperature Relation chart shows for the

given idle head pressure. If the temperature of the

condenser outlet is considerably lower than the idle

head pressure of the gauge this would indicate there is

air in the system.

Thorough leak checking is necessary. Correct the

source of the leak. Do not attempt to purge off the air

because this could result in the system being

undercharged. It is best to discharge, replace drier,

evacuate and recharge with the specified refrigerant

charge.

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Maytag MTB1893ARS Operations Instructions Page 24

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