Chapter 3 HVAC Tools, Equipment, and Service Information 53
the component, then pour about one pint of solvent into
the outlet opening of the component. Use the blowgun
to direct compressed air or nitrogen into the outlet end of
the component. Use no more than 100 psi (689 kPa) air
pressure. Always blow in reverse direction to the refriger-
ant fl ow fi rst to loosen as much debris as possible. Add
solvent and repeat until only clean solvent comes out. After
the component has been reverse fl ushed, make at least one
pass in the forward direction.
Closed Flushing Systems
Closed fl ushing systems are machines that attach
to the refrigeration system, and fl ush the system without
taking any components loose. Closed fl ushing systems
are special refrigerant cycling machines, or recovery and
recycling machines adapted to direct the solvent through
the system.
Closed loop fl ushing will not open completely blocked
passages. It will remove oil and some contamination. To
perform closed loop fl ushing, connect the machine to the
system and follow the manufacturer’s instructions.
Evacuation Pumps
Evacuation pumps are used to remove water (some-
times called moisture) from the refrigeration system.
Figure 3-29. Tank and hose fl ushing equipment. Flushing
compound is pushed through the refrigerant component by
air pressure or nitrogen, and enters the bucket for disposal.
(Robinair)
Lowering the pressure of water allows it to evaporate, or
boil, at a temperature much lower than its normal boiling
point. As the pressure goes down, so does the boiling point.
Creating a vacuum in the system also removes as much air
as possible from the system.
How Vacuum Is Measured in the Air
Conditioning System
Vacuum is a measurement of the pressure difference
between two places. Any pressure below atmospheric
pressure (14.7 psi or 101 kPa at sea level) is a vacuum.
Vacuum is measured in two ways.
Inches of Mercury
The term inches of mercury (Hg), refers to the
ability of the pressure difference to change the level in a
column of mercury. The higher the inches of mercury, the
less atmospheric pressure.
Microns
A micron is a very small unit of pressure. One micron
of pressure can move a column of mercury one millionth
of a meter, or about 1/25,000th of an inch. Therefore, a
micron is a unit of measure about 25,000 times smaller
than an inch of mercury. While inches of mercury is a
measurement of less than atmospheric pressure, microns
directly measure atmospheric pressure. A chart showing
the relationship between inches of mercury and microns is
given in the Useful Tables section of this textbook.
Electric Pumps
The most common and most effi cient type of evacua-
tion pump is electrically operated, Figure 3-30. An electric
pump can produce a vacuum of about 29.99” (300 microns).
These pumps are equipped with fi ttings that allow a gauge
manifold or other service equipment to be connected to the
pump and then to the refrigeration system.
Figure 3-30. Electric pumps are the best and most common
method of completely evacuating the refrigeration system.
(Snap-On)