12
LEAK TESTING
Once all field piping connections have been made and the braze joints visually inspected for any obvious voids or gaps introduce a
trace amount of the system refrigerant through a service gauge manifold to achieve an equalized, static pressure of 25 to 30 PSIG.
Make sure that all service and shut off valves are in the open position and slowly introduce a regulated, inert gas such as nitrogen to
increase the static system pressure to approx. 150 PSIG.
Note: Always verify the MAXIMUM system test pressure allowed for all other components in the system before pressurizing
to this level!
Allow sufficient time for the entire sealed system to achieve an equalized test pressure before physically checking all braze joints and
installed system components (both field and factory) with an electronic leak detector. Be sure to turn off the fans of any units operating
nearby or block all air movement with tarps or baffles during testing. If any leaks are indicated double check the suspected area using
soap bubbles, a strong light and an inspection mirror (if necessary). Note the location of any leaks found, reduce the system pressure
to atmosphere, repair the leak(s) (being sure to again flow low pressure nitrogen inside the system while brazing), then repeat the pre-
viously used test procedure to confirm all leaks have been satisfactorily repaired. Allow the system to stand at test pressure overnight
if possible (or several hours at a minimum), and confirm that there has been no discernable pressure decay during that time.
EVACUATION AND CHARGING
All refrigeration systems must be properly evacuated prior to charging with refrigerant. Simply purging the system with refrigerant or
skipping this important step entirely will result in system operational problems, shortened equipment life and voiding the product war-
ranty coverage. Use a deep vacuum pump which has been properly maintained and the oil recently changed. Connect the pump
(along with an electronic micron gauge) using a service gauge manifold with large bore hoses or tubing. Operate the vacuum pump
continuously during the entire evacuation process (larger volume systems may take several hours and multiple pump oil changes to
achieve a satisfactory vacuum level). Monitor the micron gauge during this time and when a minimum reading of 400 microns is
achieved, blank off the gauge, shut off the pump and observe the gauge for 10-15 minutes. At this point, if the system is tight and dry,
there should be no observed decay of the vacuum gauge reading. Break the vacuum with the correct system refrigerant and charge
as per the system design requirements.
Note: Always refer to the manufacturers charging data for the system condensing unit as the unit cooler operating charge
represents only a very small portion of the total, year round operating charge required for the entire system. Be sure
to charge any refrigerant blend as a liquid (not vapor) in order to avoid fractionization.
EVAPORATOR SUPERHEAT
In order to maximize evaporator efficiency and total system capacity a superheat reading must be taken at all system evaporators and
the expansion valve(s) adjusted when necessary to optimize coil performance. Pressures and temperatures should be monitored dur-
ing the initial room pulldown, final readings taken and valve adjustments made (if required) once the room is at or near the design op-
erating temperature and ideally, before the product has been loaded. For most applications with normal traffic patterns, stable operat-
ing room temps and uniform frost loading on the coil (SST below +32 degrees) the optimum, operating superheat at the evaporator
outlet should be in the range of 6-10 degrees. If valve control is extremely stable then lower is typically better to ensure maximum coil
performance. If box traffic and product loading is excessive, coils are located near areas of high moisture infiltration (not recommend-
ed) then a slightly higher operating superheat is recommended in order to protect the system compressor from possible valve over-
feeding. Most compressor manufacturers recommend a minimum of 20 degrees superheat at or near the compressor inlet and on
very close coupled systems some compromise may need to be made to protect the compressor. The use of a suction to liquid heat
exchanger or suction accumulator may be necessary in applications where minimum compressor superheat cannot be maintained.
TAKE THE FOLLOWING TEMPERATURES AND PRESURES
RAT
- Return Air Temperature to the unit.
SP
- Suction Pressure at evaporator coil outlet (converted to the
equivalent
SST
of system refrigerant).
ST
- Suction Temperature measured at the expansion valve
sensing bulb
For optimum unit cooler performance the superheat at the coil
outlet (
ST
-
SST
) should be as low as possible, considering
stable valve operation (little to no hunting) and as close as pos-
sible to the
RAT
.
The thermostatic expansion valve must be properly sized for the
design operating conditions of the installation and adjusted to
maximize unit cooler performance.
Always refer to the valve manufacturers installation and
operation instructions for detailed information on adjusting
the specific valve installed on the unit.
CHECKING EVAPORATOR SUPERHEAT
SP
ST
RAT
< 6”
