Part 3 - S
yst
em Design and Ins
talla
tion
Amazon Unitario Top Discharge
163
5.8 Gastightness Test
5.8.1 Purpose
To prevent
faults
caused by refrigerant leakage, a gastightness test should be performed before system commissioning..
5.8.2 Procedure
Notes for installers
Warning
Only dry nitrogen should be used for gastightness testing. Oxygen, air, flammable gases and toxic gases must not be
used for gastightness testing. Use of such gases may result in fire or explosion.
Procedure
The gastightness test procedure is as follows:
Step 1
Once the piping system is complete and the indoor and outdoor units have been connected, vacuum the piping
to -0.1MPa.
Step 2
Charge the indoor piping with nitrogen at 0.3MPa through the needle valves on the liquid and gas stop valves
and leave for at least 3 minutes (do not open the liquid or gas stop valves). Observe the pressure gauge to check
for large leakages. If there is a large leakage, the pressure gauge will drop quickly.
If there are no large leakages, charge the piping with nitrogen at 1.5MPa and leave for at least 3 minutes.
Observe the pressure gauge to check for small leakages. If there is a small leakage, the pressure gauge will drop
distinctly.
If there are no small leakages, charge the piping with nitrogen at 4MPa and leave for at least 24 hours to check
for micro leakages. Micro leakages are difficult to detect. To check for micro leakages, allow for any change
in ambient temperature over the test period by adjusting the reference pressure by 0.01MPa per 1°C of
temperature difference. Adjusted reference pressure = Pressure at pressuri (temperature at observation
– temperature at pressurization) x 0.01MPa. Compare the observed pressure with the adjusted reference
pressure. If they are the same, the piping has passed the gastightness test. If the observed pressure is lower than
the adjusted reference pressure, the piping has a micro leakage.
If the leakage is detected, refer to Part 3, 5.8.3 “Leak detection”. Once the leak has been found and fixed, the
gastightness test should be repeated.
Step 3
If not continuing straight to vacuum drying (see Part 3, 5.9 “Vacuum Drying”) once the gastightness test is
complete, reduce the system pressure to 0.5-0.8MPa and leave the system pressurized until ready to carry out
the vacuum drying procedure.
Figure 3-5.11: Gastightness test
5.8.3 Leak detection
Notes for installers
The general methods for identifying the source of a leak are as follows:
1. Audio detection: relatively large leaks are audible.
2. Touch detection: place your hand at joints to feel for escaping gas.
3. Soapy water detection: small leaks can be detected by the formation of bubbles when soapy water is applied to a
joint.
4. Refrigerant leak detection: for leaks that are difficult to detect, refrigerant leak detection may be used as follows:
a) Pressurize the piping with nitrogen at 0.3MPa.
b) Add refrigerant into the piping until the pressure reaches 0.5MPa.
c) Use a halogen refrigerant detector to find the leak.
d) If the leak source cannot be found, continuing charging with refrigerant to a pressure of 4MPa and then
search again.
5.9 Vacuum Drying
5.9.1 Purpose
Vacuum drying should be performed in order to remove moisture and non-condensable gases from the system. Removing
moisture prevents ice formation and oxidization of copper piping or other internal components. The presence of ice
particles in the system would cause abnormal operation, whilst particles of oxidized copper can cause compressor damage.
The presence of non-condensable gases in the system would lead to pressure fluctuations and poor heat exchange
performance.
Vacuum drying also provides additional leak detection (in addition to the gastightness test).
