Chapter 15 Refrigeration System Diagnosis and Leak Detection 241
compressor. Leak detection can be done by one of several
methods. Visible evidence of oil on the refrigeration system
fi ttings, compressor shaft, or evaporator drain hole means
there is a leak. Oil, swelling, or a torn spot on the rubber
covering of a hose usually means that refrigerant is leaking
from the hose.
If an obvious leak cannot be found, test for leaks using
one of the methods explained in the following paragraphs.
Note: Due to the expense and potential
environmental damage of refrigerants, any
leak detected, no matter how insignifi cant,
must be fi xed. Do not simply add refrigerant because
the leak does not seem to be excessive.
Ensure the System Is Charged
If there is no refrigerant in the system, none can leak
out to be detected. To make a leak check, there should be
a minimum low side refrigerant charge of 50 psi (345 kPa)
with the engine off. Some leaks, especially those on the
high side of the system, may require a higher charge. If
an obvious leak is so severe the system will not hold any
pressure, repair that leak fi rst, then pressurize the system.
Note: The compressors on some vehicles
are disabled by the engine control com-
puter if the refrigeration system loses its
charge. When this occurs, a trouble code is usually
set. A scan tool is usually required to clear this code
in order for the compressor to operate.
Some technicians prefer to pressurize completely
empty systems with nitrogen. If the system has only recently
begun leaking, there may be enough refrigerant left to be
detected by a sensitive leak detector. Pressurizing with
nitrogen will also allow the technician to fi nd a relatively
large leak by using the soap solution method. Refrigeration
systems can be pressurized up to about 150 psi (1033 kPa)
without damaging any of the low side components.
Remove Stray Refrigerant Vapors
Any leak detection device will produce a false leak
signal if it contacts refrigerant vapors built up under the
hood or in the shop. Before starting the leak checking pro-
cedure, run the engine briefl y to remove any vapors from
the engine compartment. If you suspect refrigerant vapor
has built up in the shop, clear the vapor using fans or the
shop ventilation system.
Using Leak Detection Devices
Modern HVAC shops use several leak testing devices.
At one time, the fl ame type halide leak detector was widely
used. Today, however, it has been largely replaced by elec-
tronic and dye detection devices. The following sections
explain how to use various types of leak testing devices. Leak
testing device construction was explained in Chapter 3.
Electronic Leak Detectors
Electronic leak detectors are more refrigerant sensitive
than the other leak detection methods. Modern electronic
detectors are extremely sensitive and can locate a leak as
small as 1/2 ounce (15 ml) of refrigerant per year.
Begin the leak detection process by turning the detec-
tor on and allowing it to warm up for about one minute
away from the refrigeration system components. Most leak
detectors will make a ticking noise that increases when the
probe encounters refrigerant. Large leaks raise the ticking to
a high pitched squeal. Many leak detectors have a display
which indicates the leak rate.
In some cases, the electronic detector’s sensitivity
must be reduced when a large leak is present or when
other engine fumes trigger the detector. A satisfactory ini-
tial detector sensitivity setting would be to detect a leak
rate of about 1 1/2 ounce (45 ml) per year. The sensitivity
adjustment knob is usually located on the detector face,
Figure 15-19.
After setting sensitivity, slowly pass the sensing tip
closely around possible leak areas and check for an increase
in the ticking noise. Also remember to pass the tip under
suspected leak areas. See Figure 15-20.
Dyes
Another leak detection method involves using dyes. A
dye is injected into the refrigeration system and allowed to
circulate. The dye will leak out along with any refrigerant
and stain the components at the site of the leak.
The fi rst refrigerant dyes were colored orange and were
contained in a small can resembling a one-pound refrigerant
can. The can was connected to the system low side through the
gauge manifold. With the system operating, the dye was drawn
into the system. After the dye circulated for a few minutes, the
technician could look for orange dye at the site of leaks.
Figure 15-19. An electronic detector will quickly locate the
smallest R-12 and R-134a leaks. Electronic detectors can be
adjusted to detect any size leak.