Why is achieving a charge so difficult on residential R-22 A/C systems?
I received an email sometime back from a supply-house area manager out west chiding me a little about the articles I have written about the dangers of using “environmentally-friendly” R-22 substitutes.
He wrote that since all his customers were now using these substitutes, the problem isn’t as dire as I had predicted.
So I asked him, “Are you seeing more compressor failures?” He told me that he’d get back to me.
Then I asked him, “Are any customers complaining about the loss of cooling capacity?” He told me he’d get back to me.
And finally, when I asked him how they are charging the systems with the new refrigerant, he told me he’d ask and get back to me.
He hasn’t gotten back to me.
Understand that the little chlorine in the R-22 reacts with and moves the hydrocarbon refrigerant oil through the system. So when a little of the oil is discharged with the gas, which happens on every compression stroke, it is all returned to the compressor by the chlorinated refrigerant.
But the new refrigerant doesn’t have any chlorine, so it doesn’t move the oil back to the compressor very efficiently. And in cases where there are suction risers (where the condensing units are on the roof and the oil must flow upward to get back) or where there are suction accumulators, the oil might not return at all and the compressor will lock up in time.
Anyone keeping track on these?
As for loss of cooling capacity, this might not be as great a problem since most units tend to be a bit oversized anyhow, though this isn’t always the case.
But when it comes to charging the systems, I doubt anyone has published any data on this that would cover all brands and sizes of systems. So I suspect most techs are simply adding refrigerant until they can feel a cool suction line, which usually means the system is overcharged and flooding back. So, the system operating efficiency is lost and the compressor oil is being diluted.
But never mind, that’s how many service techs have been doing it all along, so nothing has changed.
Why is achieving a proper charge such a difficult thing on residential R-22 A/C systems? Well, understand that liquid refrigerant arrives at the evaporator (indoor) coil where it meets what amounts to just a small precision hole. So it sprays through the hole at high pressure into a low-pressure area where the refrigerant evaporates and causes cooling. The trick here is to shoot through enough refrigerant to cool most of the coil, but not so much that liquid flows back to damage the compressor.
But the problem is that the hotter it is outside, the higher the high-side liquid pressure. And the cooler it is inside, the lower the suction pressure. So on hot days when the temperatures inside are cool, more refrigerant is flowing (danger of flood-back). However, on cooler days when the house is getting warm and stuffy, there is a problem getting enough refrigerant into the evaporator coil to do cooling. Thus, equipment manufacturers have come up with charging charts for technicians to use so as to make sure the systems are neither overcharged nor undercharged. These provide a critical accuracy of plus or minus a half-ounce.
This is the problem with “by gosh and by golly” field-guesstimated charging methods.