11
Model 20
Refrigeration Principle
Section 6
Refrigeration Principle
The insulated evaporator assembly has copper tubing
coiled and soldered around the outer diameter. An
automatic expansion valve sprays liquid refrigerant
through the copper tubing. This refrigerant rapidly
boils, picking up heat from the solution in the
removable basin. As a low pressure gas, the
refrigerant now travels out the copper tubing and down
to the compressor.
The automatic expansion valve is pre--set from the
factory at 9--10 PSI. To make any adjustments to the
automatic expansion valve, place the low side line of
a gauge set to the low side access port near the
compressor. Place the pushbutton control switch in the
ON position. While observing the gauge, turn the
adjustment knob of the automatic expansion valve. A
clockwise adjustment increases the low side pressure.
A counterclockwise adjustment decreases the low
side pressure.
Low Side:
The point between the outlet of the
automatic expansion valve as it enters the insulated
evaporator, all the way to the compressor.
Low Side Pressure:
Automatic expansion valve
setting of 9--10 PSI.
The compressor is a pump which circulates refrigerant
throughout the system. This compressor receives the
low pressure gas from the insulated evaporator. It
compresses the gas and sends it to the condenser as
a high pressure gas. As a safety measure, the
compressor has an internal overload. Should an
overload occur, the compressor will automatically shut
down. Once it has cooled, the compressor will start up
again.
The condenser receives the high pressure gas from
the compressor. A fan motor and blade pull air through
the rear of the unit, and across the condenser. At this
time, heat is removed from the refrigerant gas and is
dissipated out the sides and front of the machine.
Once heat is removed from the gas, the refrigerant
turns into a liquid and drops to the bottom of the
condenser.
The filter dryer receives the liquid refrigerant from the
condenser. It filters impurities from the refrigerant
before it reaches the automatic expansion valve. Any
time the refrigerant is discharged from the system, a
new filter dryer must be installed.
The heat exchanger consists of the liquid line and
suction line soldered together. This is used to sub--cool
the liquid refrigerant in the high side before it reaches
the automatic expansion valve. The colder the
refrigerant is before it reaches the automatic
expansion valve, the more heat it will pick up when it
enters the insulated evaporator. More importantly, the
heat exchanger vaporizes any liquid refrigerant that
might leave the insulated evaporator before it reaches
the compressor.
If the frozen slush in the removable basin was left
unattended for prolonged periods, the liquid refrigerant
entering the insulated evaporator would not be able to
boil off rapidly enough, due to the lack of heat. This
would cause the refrigerant to leave the insulated
evaporator as a liquid. If this occurred, frost would build
up near or on the compressor. Liquid refrigerant
allowed to enter the compressor would boil rapidly
because of the heat in the compressor. This violent
boiling action would allow the refrigerant to pick up
excessive oil in the compressor.
If the machine is subject to this condition, the
excessive oil will separate from the refrigerant as it
enters the insulated evaporator. The oil will occupy
space that the refrigerant must occupy to sufficiently
remove heat from the solution. In addition, oil leaving
a compressor could cause damage to the compressor.
To correct an oil--logged insulated evaporator, open
the automatic expansion valve to approximately 20
PSI. Pour hot water into the insulated evaporator and
place the unit in the ON position. This will cause the
refrigerant to flow into the insulated evaporator very
rapidly. It will then boil violently because of the hot
water. This violent boiling will allow the refrigerant to
pick up the oil and carry it back down to the
compressor. Once the hot water begins to cool, place
the machine in the OFF position. Adjust the automatic
expansion valve to the original setting.
High Side:
The point between the outlet of the
compressor, all the way to the expansion valve.
High Side Pressure:
Should be maintained between
180--200 PSI, depending on room ambient conditions.
