Please note, this method to recharge a refrigerator is for domestic and light commercial refrigerators and NOT cold rooms.

Although cold rooms use a very similar method, there are differences in re-charging when there is a solenoid valve which will be explained!

Re-charging a refrigerator requires the following checklist:

• A correctly flushed system
• A new filter/drier
• Proper vacuum evacuation
• All joints correctly brazed on connected
• Cross-reference with the compressor specifications on what refrigerant to use. NEVER ASSUME! 

If there are evaporator fans on the unit, they will need to be disconnected when charging the refrigeration unit!

Requirements

• Manifold gauges
• Appropriate refrigerant
• Bucket of warm water
• Patience

Method

This process of re-charging the system which will be explained in this chapter is the most effective way to re-charge a refrigerator, cold room and air-conditioning unit.

There are some preferences to re-charging a refrigerator by using pressure indicators according to a gas chart or weighing refrigerant, or even judging by flow via a sight-glass, however, this method is by far the best because it uses practical logic of science which I will explain further.

Although there have been many contradictions and objections to this method, however, after re-recharging over 1,200+ refrigeration units, I have yet to have a come-back or a single compressor failing on me using this method.

Applying the science

When the refrigerant enters the evaporator, it needs to have an equilibrium of pressure to ensure that even temperature dissipation is applied throughout the evaporator equally. In other words, the entire evaporator should be equally “cold” in order to ensure sufficient and effective cooling.

If only half the evaporator is freezing, this is an indication of low refrigerant. Therefore, if we consider this, then an equally “cold” evaporator is a good indicator of a well-balanced system.

As refrigerant exits the evaporator it begins to alter its state. As soon as it exits the fridge container (such as a cold room or a fridge cabin), it becomes exposed to natural conditions causing it to heat up. Influences such as air moisture, and temperature according to the environment will affect gaseous state changes.  Because of these external factors, it makes absolute sense to recharge a fridge according to the environment.

Because we have other factors such as winter and summer, this can also have a huge impact on fridge dynamics and cooling. This is often referred to as a winter and summer charge, specifically on air-conditioners, but applying refrigerant and monitoring the freeze-back on the suction line to the compressor, can minimise the need for a winter and summer charge.

The trick to this is to charge a refrigerator, including cold rooms, chillers, and beverage coolers, to the point where there is the frosting of the return pipe no less than the threshold distance from the compressor.

The reason for this is that when the gas is returning, it needs to heat up again before it enters the compressor. If refrigerant enters the compressor as a liquid, it can put a serious strain on the pistons.

Therefore, by leaving a slight frosting up to the point where it is less than the threshold, we are sure of equal evaporative cooling as well as satisfying a balance between the summer and winter charges.

Freeze-back thresholds

• Cold rooms – no less than 500mm
• Standard refrigerators – no less than 300mm

STEP 1: GAUGE CONNECTION

• Connect the gauges to the compressor and appropriate refrigerant as shown.
• Remember to ensure that the Shrader inner valve has been replaced on the compressor.
• Tighten all the connectors, except the YELLOW line. This needs to be loose to PURGE the lines.

STEP 2: PURGING THE GAUGE LINE

• Open the refrigerant slightly to allow gas to escape on the YELLOW line on the gauges.
• Just a slight amount is needed to escape in order to purge any air out of the line.
• With the refrigerant can open, tighten the YELLOW line on the gauge
• The line is now purged and you can start charging the unit.

STEP 3: CHARGING

• Open the refrigerant canister to full.
• Open the Low-Pressure gauge slightly to allow refrigerant into the system through the compressor.
• Do not add too much, all you need to do is charge the unit until it is out of negative pressure. Charge until approximately 10psi which is a safe zone to prevent the compressor from going into negative pressure when turning on.

STEP 4: APPLYING CHARGE

With the system out of negative pressure, turn on the refrigerator (still with evaporator fans off).

1. You will notice the gauge drop to approximately 5psi or 0psi. Open the gauge to add more refrigerant.
2. Monitor the intake by opening and closing the gauge in 5pis increments. This will ensure that you do not overcharge the system and waste gas.
3. Depending on the unit size, there should be some cooling on the capillary tube (or TXV). This is an indicator that the system is free-flowing.
4. Continue to slowly add refrigerant until you notice that the evaporator is starting to become cold. Pay attention to the return line exiting the evaporator. This should start becoming increasingly cold.
5. You need patience for this, however, is should take you approximately 25 minutes until the evaporator is fully cold.
6. Feel the discharge on the compressor which should be relatively hot and the return line on the outside of the fridge container becoming cooler.
7. As soon as the evaporator is cold and the return line cool, let the fridge run for a 5 minutes before turning it off for 10 minutes. This allows the refrigerant to balance in the system.
8. Turn on the fridge again and let it run for 10 minutes and monitor the freeze-back thresholds.
9. You may need to apply a little more refrigerant and depending on the unit, the psi value should be between 15psi and 32 psi.
10. As soon as the freeze-back threshold is satisfactory, turn off the fridge to connect the evaporator fans (where applicable)
11. REMEMBER! Never turn a fridge on immediately after turning it off as this can cause strain on the compressor. Always wait about 5 minutes.

While you wait for the fridge to start reaching temperature (place your thermometer in the cabin and monitor the desired temperature), you can keep checking on the suction line freeze back and inspect the correct running of all fans, compressors etc.

As soon as the fridge reaches the correct temperature, ensure the thermostat is set correctly. The fridge will now be fully working and hassle-free if all steps have been taken.

24-hour to 48-hour inspection

Just because a fridge is starting to get cold, it does not mean the unit has settled.

After re-charging any refrigerator, it is good practice to return after a few days to monitor the freeze-back. The reason we wait 24 to 48 hours is so that it gives time for the refrigerator to balance and get a natural satisfaction of operation.

The first sign you need to look out for is if there is ice building up too close to the compressor.

• If there is excessive ice build-up onto the compressor, slowly release refrigerant a little at a time until you will physically notice the ice melting and moving back. Please note that this is for minor ice-build-up and not huge blocks.
• If the evaporator is only freezing halfway, this is low refrigerant and needs slow topping up.

After becoming familiar with this method and applying the steps, it is guaranteed you will not have any callbacks or issues with the unit you are working on.