56 Auto Heating & Air Conditioning
The spectrograph type of antifreeze tester depends on
the refractive (light bending) properties of the coolant mix-
ture. Coolant is drawn into the spectrograph and observed
through a prism. The optical pattern of the coolant deter-
mines the amount of water and antifreeze in the system.
Figure 3-37 shows a typical spectrograph antifreeze tester.
Test Strips
Test strips can also be used to test antifreeze concentra-
tion. Test strips consist of a chemically treated paper strip that
is dipped into the vehicle radiator fi ller neck, Figure 3-38. The
color change of the test strip indicates the amount of antifreeze
present.
To use a test strip, make sure the engine has thoroughly
cooled off. Then remove the radiator cap or reservoir cap
as necessary. Dip one of the test strips into the coolant for
about one second. Remove the strip, shake off the excess
antifreeze, and wait until the strip changes color. Waiting
time is usually about 15-30 seconds. Then compare the
color of the strip with the color chart on the strip package.
As a general rule, a darker strip indicates a higher percent-
age of antifreeze in the coolant.
Combustion Leak Testers
Internal engine combustion leaks are caused by
blown engine head gaskets or by cracked heads or blocks.
Combustion leaks will affect coolant circulation and heater
operation, cause coolant to be pushed out of the radiator,
and will contaminate the cooling system internals with
exhaust byproducts. To prevent further damage, combus-
tion leaks must be corrected as soon as possible.
It is sometimes diffi cult to tell when an engine develops
an internal combustion leak. If the leak is small enough
there are no telltale bubbles in the coolant, or if the leak has
not allowed water to get into the engine oil, the technician
must use a combustion leak tester, Figure 3-39. To use the
combustion leak tester, attach it to the radiator fi ller neck.
With the gauge attached to the fi ller neck, start the engine
and allow it to idle. Exhaust gases will cause the chemical
in the tester to change color.
Service Literature
The technician must refer to many sources of service
literature to properly service HVAC systems. While modern
HVAC systems operate from the same basic principles,
Figure 3-37. Spectrograph type antifreeze testers are accurate
and simple to use. (Leica)
Figure 3-38. Coolant test strips can be used to test coolant for
concentration, as well as pH, which indicates the coolant’s
acidic level. (MVCC, Jack Klasey)
Figure 3-36. A—A hydrometer is the tester most commonly
used to check the concentration of antifreeze in cooling systems.
Hydrometers are simple to use and relatively accurate. B—Some
hydrometers have a temperature-correcting device that compen-
sates for specifi c gravity between hot and cold coolant.
A B