It’s essential to know how to proceed and to know the refrigerant fluids.
The correct refrigerant charge is critical to the refrigeration system’s performance. Therefore, besides a good quality refrigerant fluid, proper procedures to perform the charge must be closely followed.
CAUTION DURING THE VACUUM PROCESS It’s important to perform the vacuum process using a pump that reaches 500 microns, with a 3 CFM capacity or greater. It’s recommended that the vacuum process be performed both on the system’s low pressure side, connected to the process passer, as well as on the system’s high pressure side, at the extra filter drier tube. Good practice dictates that the process be maintained for 20 minutes after reaching the expected level.
It’s worth remembering that, before receiving the refrigerant charge, the system needs to undergo a properly executed evacuation process to remove air and moisture. After cleaning the system, it’s necessary to check for leaks by performing a leak test. The professional must check the compressor label for the compatible refrigerant type and check the refrigeration system for the correct amount that needs to be inserted. If this information isn’t available, consult the equipment’s manufacturer.
Additionally, the equipment that will be used for charging should be on hand:
- Metering bottle (or metering cylinder);
- Charging cylinder with graduated scale;
- Precision scale to 1 g.
Main procedures Once you have obtained information about the type and amount of the refrigeration system’s recommended refrigerant, the charging procedure can start. A good tip to really visualize the procedures and confirm that explanations are well understood is to watch the video about changing compressors that’s available on the Refrigeration Club’s website. There a step by step video of the charging process can be followed. See below the steps for this important procedure:
1. Weigh the empty metering cylinder (with vacuum performed or purged); 2. Use the tare to zero the scale (when available) and add the recommended gas charge. Or otherwise add the gas charge weight to the cylinder weight. 3. Connect the receiver metering cylinder to the process tube through the manifold. Leave the manifold’s high and low valve open. 4. Release the gas charge into the system with the compressor turned off; 5. Wait for the necessary time to equalize the pressure between the cylinder and the manifold for high and low; 6. To ensure that the cylinder is completely emptied after equalization, close the high valve, turn on the compressor and wait a few minutes with it in operation; 7. Close the metering cylinder valve, then close the low valve, disconnect the cylinder and weigh it to verify that all charge was removed; 8. If the entire charge was removed, proceed with the next steps; otherwise, perform the manifold connection again; 9. After completing this step, it’s time to close the tubing. With the compressor on, crimp the process tube closest to the quick-coupling in two places; 10. Turn off the compressor, cut the tube and seal it with solder. Check for leaks;
Note: For blends, it’s necessary to perform the charge with the refrigerant in a liquid state, to ensure the correct mixture ratio.
[box side="alignright" color="box-cinza" pos="vertical"] PROBLEMS WITH INCORRECT CHARGE The refrigerant charge operation requires great care from the contractor. If there is excess charge, there will be excess cooling capacity. The evaporator’s temperature will be too high and heat exchange will not occur. Additionally, the compressor may suck in the refrigerant fluid which may cause rupture of the cylinder seals or break other components. In the case of lack of refrigerant fluid, the system will not perform adequately, due to insufficient cooling capacity. One consequence of this is that the compressor has to work harder, staying on up to 100% of the time – which causes extra wear as well as reduces its durability.
Curiosities about the gas charge In household refrigeration, most systems work with a refrigerant quantity of less than 150 g. For commercial refrigeration these values can reach 900 g of gas. This makes it even more important to follow proper procedures for gas charging, using the correct equipment for this operation, where a change of a few grams, more or less, can have negative impacts on the system’s performance. It must also be remembered that charges vary greatly depending on the refrigerant fluid type. For example, a 280 to 300 liter refrigerator normally needs 90 to 120 grams of R134a. However, if R600a is used, the charge will be from 36 to 48 grams.