Chapter 3 HVAC Tools, Equipment, and Service Information 55
Pressure and Leak Testers
The quickest way to locate coolant leaks is to use a
pressure tester, Figure 3-35. The pressure tester contains a
pump to pressurize the cooling system. With the system pres-
surized, coolant will leak out. The technician can observe
the leak and determine its source. The pressure tester also
contains a gauge, which allows the technician to place the
proper amount of pressure on the system, and helps in locat-
ing leaks in the engine or other inaccessible places.
To use the pressure tester, make sure there is no pres-
sure in the cooling system, then remove the radiator cap.
Warning: The cooling system must be
depressurized and cool before performing
this test.
Add coolant if the system is low. The cooling system
must be full for the leak test to work properly. Next, install
the pressure tester on the radiator fi ller neck. If necessary, use
the proper adapter to ensure a good seal. On some vehicles,
the coolant reservoir is pressurized and the tester must be
installed on the reservoir cap. Apply pressure until the gauge
shows the pressure rating stamped on the radiator cap.
After pressurizing the cooling system, place the gauge
in a location that will not bend the attaching hose. Observe
the gauge for several minutes. If the gauge needle begins
to drop, a leak is present in the system. Next, check the
engine and cooling system for dripping coolant. Slight
leaks may be located even when the gauge remains steady.
After pressure testing the system, slightly bend the hose at
the fi ller neck fi tting to remove pressure. Then remove the
tester from the fi ller neck, clean off the fi tting, and store the
tester in its case.
Antifreeze Testers
If the engine coolant contains incorrect percentages
of antifreeze and water, problems may occur. Too little
antifreeze may cause the coolant mixture to freeze in cold
weather, and will not protect the system properly against
corrosion. Too much antifreeze in the mixture may actually
raise the freezing point.
To check the exact percentages of antifreeze in cool-
ant, an antifreeze tester is needed. There are two kinds
of antifreeze testers, the fl oat and the spectrograph. The
fl oat type, Figure 3-36A, makes use of the fact water and
antifreeze have different weights. The weight of a liquid is
usually called its specifi c gravity. Since antifreeze is heavier
than water, a greater amount of antifreeze in the coolant
will cause the fl oat to rise higher in the mixture. The fl oat
is calibrated and the percentage of antifreeze can be read
by observing how high the fl oat rises in the mixture. Some
hydrometers have a thermometer that allows the user to
compensate for coolant temperature, Figure 3-36B.
Figure 3-33. A modern charging station contains all of the
devices necessary to refi ll a refrigeration system. (RTI)
Figure 3-35. This coolant pressure tester is shown installed on
a vehicle. Cooling system leaks can be observed visually, or by
watching for a pressure drop. To test the radiator cap, special
adapters are used to attach the cap to the pressure tester.
Figure 3-34. Some charging stations use a manual air purging
device. The technician vents the tank until the red and green
needles line up. Most charging stations air purging devices are
automatic. (Nissan)
Air purge indicator
Red
needle
Green
needle
50
150
200
250