It is not uncommon for HVAC technicians to overcharge refrigeration systems when they service them. This is a very easy mistake to make because there are so many different systems on the market and it is easy to make mistakes and misinterpret how much refrigerant they need to put into a unit. The problem is compounded by the fact that many of the symptoms of an overcharge are similar to symptoms of other problems, so misdiagnosis of HVAC faults is easy too.
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What Does Overcharging Do?
When a system is overcharged with refrigerant, the system operating pressure and temperature will be overcharged, and this will make the system less able to cool things down. Overcharging of your refrigerant will cause an increase in the pressure of both the low and high side of the system. The system will become less efficient, and more expensive to operate. It may still work, but it will take more energy and it will not cool air down as efficiently or as effectively as it should.
There is some risk, with certain types of HVAC unit, that overcharged refrigerant could flood back into the compressor motor. If liquid refrigerant is able to enter the motor, then it could cause lasting damage. The compressor motor has numerous moving parts which expect to be compressing a gas, and they are not designed to handle liquids. When liquid enters the motor, this is known as ‘liquid slugging’, and it could quickly destroy the motor.
Overcharge can also cause some other rather unusual effects. In some cases, the electric motor could fail to start or even start running backwards as a reaction to excessive refrigerant pressure. High refrigerant pressure in an A/C unit can cause rotary vane type or scroll-type refrigeration motors to start operating backwards. This is more likely to happen in older units, because it is a combination of high pressure and a temporary loss of power that can cause that fault. Newer units often have a timer/anti-restart control that will prevent the compressor from restarting backwards.
The fault was something that would frequently happen with older units if they were overcharged and the owner accidentally turned the power off at the switch, then turned it back on very quickly. The high pressure would ‘push’ the motor back, and when the power was restarted the motor would continue in the direction it was previously running. The anti-restart control on newer units mitigates this.
Overcharging Commercial Systems
While commercial systems are built to be very resilient, they can still have some issues. A small overcharge of a commercial system may simply result in some gas entering the receiver, but bigger overcharges can cause a lot of problems, including damage to the Thermal Expansion Valve (TEV), or a freeze-up of the TEV. This would cause the system’s cooling to fail completely.
Overcharge can also cause liquid refrigerant to run too deeply into the evaporator coil which can reduce cooling pressure significantly.
Measuring Your Unit’s Charge
One of the reasons that HVAC overcharging is such a serious problem is that there is no simple way of knowing exactly how much refrigerant is in a unit. The only two occasions when we truly know the charge level is when the equipment is brand new or it has been fully evacuated because at that point the answer is zero, or close enough to zero, and then when the system has been evacuated and given a measured charge.
In smaller home systems where there is no receiver, the refrigerant charge needs to be incredibly precise so as not to risk damaging the unit. In bigger systems, there is a receiver that will act as a buffer, so if there is a small amount of excess charge then it will be caught by the receiver before it does damage.
Thousands of HVAC systems run for year after years without leaking, and it is typically assumed that the units have the same amount of charge in upon inspection as they did the day they were installed. In truth, there is a very slow leak over time. This leak is so small as to be considered zero and is the reason that pressures do not change for years and years unless the system is damaged. If you keep your unit in good condition and inspect it regularly you should not need to recharge it. If a fault develops and your technician suggests a recharge, then be sure to ask them to check for leaks at the same time, to ensure that there is not a more serious underlying issue.
Don’t Fall for Recharge Scams
As the R22 phase-out approaches you may find that you start getting unsolicited contact from scammers who say that your HVAC system needs recharged. They may even bring up the phase out as a reason for needing your ‘refrigerant levels checked’. It is important to have your HVAC units serviced regularly, but you should not respond to such unsolicited contact. Do not let anyone pressure you into changing your HVAC unit or swapping to a drop-in replacement without doing your own due diligence first.
The price of R22 is going to increase dramatically over the coming months, and it is true that R22 is not particularly environmentally friendly. If you can afford to replace an old HVAC unit with a newer one that runs a lower ODP and GWP refrigerant then that is the ideal option. If you cannot afford to replace your unit, then retrofitting it to run something like R410A or using a drop-in replacement is a perfectly good option and something that you can do at your leisure. As long as your unit is in good working order and you are not knowingly allowing it to leak R22 into the atmosphere, you are not breaking the law. Anyone who tries to sell you a refrigerant recharge citing the “Montreal Agreement” or changes in the law surrounding HCFCs is simply trying to exploit a lack of understanding of the changes.