KRA Refrigeration System Installation, Operation & Maintenance Manual
L-3571 ENGLISH
13
4.
The best way to make sure the unit is charged properly is by the subcooling method. This will ensure that you have a
good liquid seal to the TXV with no flash gas or vapor. Typical subcooling is 6 to 10°F/-14 to -12°C depending on the
condensing temperatures. Refer to Figure 10: Refrigerant Pressure-Temperature Chart, page 21.
A
DJUSTING
THE
TXV
On rare occasions,
a qualified technician may need to make an adjustment,
but these adjustments are slight. Use a wrench
to remove the nut covering the superheat adjustment valve stem. This exposes the valve stem. Once the system has had
sufficient running time to stabilize the box temperatures, adjustment should be made in 1/4-turn increments only. Use the
wrench to make adjustments. After each incremental adjustment, allow 15 to 20 minutes for the expansion valve diaphragm to
stabilize.
Looking at the stem-end of the valve:
•
Turn the valve stem clockwise to close the valve; this will decrease the flow of refrigerant and increase the superheat.
•
Turn the valve stem counter-clockwise to open the valve; this will increase the flow of refrigerant and decrease the
superheat.
•
One full turn of the valve stem equals 4.5° of superheat.
•
Follow directions with the valve. Replace the outer nut, and tighten to 3 ft-lbs. Insulate valve and bulb fully.
TXV M
ETERING
D
EVICE
If service or replacement is needed, follow manufacturer’s recommendations for more information. Call Dometic Technical
Support.
S
IGHT
G
LASS
See “Sight Glass/Moisture Indicator” on page 9“ in the “Installing the Refrigeration System” section.
USER MAINTENANCE
S
EAWATER
S
YSTEM
Check the seawater strainer daily. Remove any debris. If you are in waters where jellyfish or other debris are a problem, you
may find it necessary to add a strainer on the outside of the through-hull fitting.
Verify that all seawater connections are tight, and check for water flow from the overboard discharge. The centrifugal seawater
pump does not need any regular maintenance.
D
EFROSTING
Defrosting of your freezer box is required to keep the unit working at peak performance. Defrost the unit whenever more than
1/4" (7 mm) of ice or frost has accumulated on the plates or box sides.
To defrost, remove all the contents from the box and remove drain plug (if applicable), then disconnect the power to the KRA
unit. Leave unit off until all ice has melted. Be sure to replace drain plug once unit has finished defrosting (if applicable).
To accelerate the defrost process, remove plug and use fresh water to melt ice and rinse the box clean. Never use a mechanical
device to remove ice. Damage to box liner is not covered under Dometic Warranty.
W
INTERIZING
THE
S
YSTEM
Make sure all water has drained from the refrigerated box. On seawater-cooled units, close the seacock, and remove inlet hose
from pump and outlet hose from unit to allow all water to drain from the system. Drain and clean seawater strainer.
NOTE
Check ability of vacuum pump to achieve 200-400 microns by connecting micron gauge directly to pump. If it does not
achieve 200-400, service or replace pump.
NOTE
If moisture has been a problem, refer to Refrigeration Bulletin 02-1 for instructions on clean up. This bulletin is
available on the Marine Resource Center under Technical Field Notices: “Control of Moisture in Refrigeration
Systems” (FN#175-I2).
CAUTION
System contains R-404A refrigerant. Recovery machines containing mineral-based oils should not be used.
