located in the liquid line between the receiver and the
NOTE: Use the back-seat position when installing
evaporator. The refrigerant passes through a filter cloth,
a pressure gauge on the service valve.
where foreign material is trapped; it then goes through a
MID-SEATED.--When the valve is mid-seated,
porous material of activated alumina or silica gel
both the system and servicing/gauge ports are open.
enclosed in a metal container, where moisture is
This position is used during servicing or external
absorbed from the system.
monitoring. To mid seat a service valve, first back seat
If the drier-strainer is frosted or feels cooler than
the valve, and then turn the valve stem one quarter turn
the liquid line entering the drier, it indicates that the
clockwise. This moves the valve stem slightly to the left
drier is clogged, and the liquid refrigerant is vaporizing
and allows gas to flow into the gauge port.
in the drier. In this situation, the drier cartridge must be
Vibration eliminators absorb and remove inherent
vibration in copper tubing caused by floating
The air filter is located in the inlet to the ventilation
components. They are constructed of an accordion-like
blower, and while technically not a component of the
phosphorous bronze tube with copper fittings at each
refrigeration system, it plays an important part in air
end to facilitate joining with the system tubing. The
conditioning. Filters are used to remove dust, bacteria,
accordion-like folds in the material are called
and odor from the air. The two types of filters in
common use are the dry filter and the viscous filter.
On some air-conditioning systems, a simple loop is
The dry filter removes dirt by passing air through
made in the refrigerant tubing itself. The loop permits
small openings in felt, spun glass, or paper screens.
vibrations to be absorbed in the extended length of
Some dry filters can be cleaned and reused, but most are
Liquid Line Sight Glass
The viscous filter depends on dirt adhering to a
surface covered with a viscous fluid or oil. When this
The sight glass is a visual indicator used to visually
type of filter gets dirty, it is cleaned, retreated with a
determine the condition of the refrigerant entering the
viscous fluid or oil, and reused.
thermal expansion valve. The sight glass is located on
the inlet side and as close to the thermal expansion
valve as possible. The appearance of the refrigerant
passing through the sight glass should be clear and free
Controls of an air-conditioning unit may be classed
of bubbles. If the sighting indicates a cloudy or milky
as two distinct types--operating and safety. Operating
appearance, the level of refrigerant is low. The milky
controls maintain the desired conditions. The safety
appearance is caused by tiny refrigerant vapor bubbles
mixed with the liquid refrigerant.
The receiver outlet valve, referred to as the king
valve or liquid line shutoff valve, is located on the
output side of the receiver tank. This valve is used when
it is necessary to trap the refrigerant in the receiver and
The drier-strainer (fig. 11-14), also called a
dehydrator, is used to remove foreign matter and water
from the system. Foreign material can clog small
openings, and water can freeze in the expansion valves,
causing the system to malfunction. The drier-strainer is