Charging
Part 2

Let us assume that you have located and repaired the leak which caused the undercharged conditions. You now wish to top up the refrigerant charge and have hooked up a jug of the appropriate refrigerant. Click the Charge button to open the low side hand wheel on the gauge set and start charging. Notice all the things that change as you are charging. The yellow colour is used to indicate the route that the refrigerant takes when you allow flow from the jug. Gas will flow because the pressure in the jug is greater than the pressure in the low side of the system. High pressure flows to low pressure just as high temperature flows to low temperature. When you open the low side hand wheel you can see the suction pressure increasing on the low side gauge. You can also notice a slight increase in high side pressure and you now know why.

Stop   Charge

You can see that there is a liquid/vapour interface in the refrigerant jug and that you are drawing refrigerant from the vapour portion. This vapour is being introduced into the suction of the compressor and there is nothing wrong with that. This method works well with small to medium sized systems but if you need to charge a large system you might be there for very long time indeed. If you vapour charge for several minutes you will notice a decrease in available pressure from the jug. You will also notice that the jug is getting colder and colder. That makes sense because we know low pressure goes hand in hand with low temperature. We can't get away from the laws of physics. When you draw off some vapour from the jug the Pressure Temperature Relationship forces some liquid to flash into a gas to make up for the vapour you just removed and keep the Pressure Temperature Relationship in balance. But by changing state that liquid has created the refrigeration process and removed heat from the surrounding area which in this case is the rest of the liquid refrigerant in the jug. If you continue vapour charging long enough the drum may get so cold that you lose all of your pressure differential and can no longer continue. One solution is to warm up the contents of the jug. Don't even think of playing a torch on the jug. You must never do that. A safe method to warm up a jug is to place it in a pail of warm water or if you prefer run warm water over the jug in a sink. Keep a gauge in place so you can monitor the pressure at all times. Develop safe working habits, there are more than enough dangerous circumstances to go around without creating any of your own.

We are still in need of a method to charge a large system...