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48.
Charging the Compressor Double Refrigeration
Instructions on how to charge the refrigeration system with R134a gas and set the expansion valves.
IMPORTANT ADVICE - It is essential that only fully qualified, licensed Refrigeration Engineers attempt the following
procedures. All equipment used to service the system must have been used exclusively for R134a refrigerant (including the
connection hoses) and not with any other refrigerant. It is also important to filter the refrigerant gas from the charging cylinder
to eliminate any impurities.
Before to proceeding, it is essential that the calibration of the trolley probe is correct.
How to charge the gas in the refrigeration circuit - There are two cases where charging may be necessary – first, refrigerant has
to be added to “top-up” the circuit and second, to charge the system when there has been a complete loss of the refrigerant
charge.
Partial Charge: Set the refrigeration temperature with the touch-pad to 1°C and start the refrigeration. When the display
indicates 1 degree the expansion temperature must be –24 / -26 for the double refrigeration systems. If these values are
different, add or remove a small quantity of refrigerant and wait a couple of minutes until the reading settles to the new value.
If the new reading is different from –24 / -26 repeat the above operation until the correct expansion temperature is achieved.
Complete Charge: When the compressor has been changed or a gas leak repaired it is very important to ensure a full vacuum
is achieved before recharging. The vacuum operation must last at least 30 minutes and should be continued for up to 60
minutes. To be certain that the circuit is completely vacuumed, monitor for another 45 minutes. After turning off the vacuum
pump the manometer needle should oscillate less than 0.2 to 0.3 bar (3 to 4.5 psi).
For new installations, when the vacuum cycle is complete, the manometer needle must remain steady after the pump is turned
off.
When the vacuum cycle is complete, the refrigerant charge can start. With the compressor turned off slowly charge the system.
About 50 grams (about 2.50 oz.) of gas will be needed to saturate the circuit. Insert the gas from the charging valve put on the
high-pressure side. The complete charge is 230 grams (about 8.11 oz) for the double refrigeration systems. To finish the
charge, close the manifold-charging valve and start the compressor. After running approximately half minute, very slowly add
more refrigerant until the complete charge of 230 grams is reached.
The expansion valves are pre-calibrated and should not be altered under normal conditions.
SETTING –Setting the expansion (TX) valves is a delicate operation and must be done while monitoring the expansion
temperatures read on the manometer. The minimum values set on the charge valve operate as follows:
Switch the trolley on, enter programming mode and set the refrigeration temperature at 1 degree in both sections. Switch off
and on to start the trolley. The refrigeration will start to cool down the cold section first. Once the cold section set temperature
has been achieved, the refrigeration will change over to cool the oven section.
First set the “cold” section – to complete this operation the trolley doors must be closed and the oven solenoid valve closed
(disconnect plug CN5 from the power card).
Keep the refrigeration system running. When the indicated temperature on the display is +5 / 6 °C (+41 / +45°F), the expansion
temperature should be –24 / -26 °C. If the reading differs from this values carefully adjust by turning the adjusting screw by
fraction of turn at a time. Wait a couple of minutes until the expansion reading settles to the new value. If the new value still
differs from –24 / -26 °C, repeat the above procedure.
Reconnect CN5 and repeat the same operation for the oven side. The cold side set temperature has been achieved, the trolley
will now cool down the oven section.
Keep the refrigeration system running. When the indicated temperature on the display is +5 / 6 °C (+41 / 45 °F), the expansion
temperature should be –24 / -26 °C. If the reading differs from these values carefully adjust by turning the adjusting screw by
fraction of turn at a time. Wait a couple of minutes until the expansion reading settles to the new value. If the new value still
differs from –24 / -26 °C, repeat the above procedure.
Reprogram the refrigeration temperatures in both sections to the correct working values.
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