"An epidemic of moisture-related problems are causing more system failures today than ever before in the history of air conditioning and refrigeration," said Paul Appler a technical speaker at the State of Alabama's mandated Continuing Education Program for HVAC/R Contractors.

Appler, director of research, Cliplight Mfg., Toronto, Ont., presented the state-approved "Repair and Servicing R-410A/POE and R-22/Mineral Oil-Related Systems" last April to full-capacity classes of HVAC/R service techs at the Alabama Johnstone Supply branches of Birmingham and Huntsville, respectively.

"I think service techs are finally understanding that moisture is now public enemy number one based on the many moisture-related questions they asked during the four-hour class," said Larry Brudi, the program's host and owner of five Johnstone branches in north central Alabama and middle Tennessee.

While R-410A/POE systems readily react with water or "hydrolyze" to form acids and alcohol that lead to accelerated system corrosion, Appler also said R-22/mineral oil systems can also develop similar problems such as waxing particulates that restrict thermostatic expansion valves (TEV). "Moisture is an old adversary regardless of the system, but now it's even more threatening because of the efficiency advancements of today's systems," said Appler, who also presented the same topic to Johnstone Supply in Fresno and Visalia, Calif.; The Training College of the Sequoias, Visalia; HVAC contractor, Arctic Mechanical, Rancho Cucamonga, Calif.; and Refrigeration Supply Distributors branches in Buena Park, Pomona, Anaheim, and Monterey Park, Calif.. 

However, the good news is chemical-based drying agent additives, triple evacuations, liquid line drier replacements and other technology can help remove and prevent and greatly reduce system moisture. When combined with ac/r repair fundamentals outlined by organizations such as the Air-Conditioning Refrigeration Institute (ARI), Arlington, Va., and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), Atlanta, Ga., moisture-related problems can be virtually eliminated or at least minimized.

Shortening Triple Evacuation Time

Commercial refrigeration service contract customers typically can afford their service company's lengthy full-fledged triple evacuation procedures that ASHRAE recommends to boil off moisture in a system, according to Appler. However the average residential central air conditioning customer typically can't afford two to four-hour service calls. "AC/R associations recommend a pull-down between 500 to 1,000-microns with the ability to hold the vacuum for at least an hour, but residential techs don't have that kind of time or don't feel comfortable billing customers for it," said Appler, who is the inventor of HVAC/R tools such as Super Seal Classic™ and Super Seal Total™ refrigeration system leak sealants, and Dry R™, a drying agent designed to eliminate up to 60 drops of system moisture per application.

Instead, Appler recommended a leaner five-step evacuation approach that reduces service time on residential air conditioners while still assuring the greater amount of moisture is removed.  The steps are:

1.    Using a two-stage vacuum pump and evacuate down to 1,000-microns.

2.    Once 1,000 microns is reached, immediately break vacuum with 15-psi nitrogen and hold for 10 minutes.

3.    Evacuate to the 500 to 700-micron level.

4.    Immediately break vacuum again with 15-psi nitrogen and hold for 3 minutes.

5.    Evacuate down to 500-microns and hold for 10 minutes.                

On a typical residential unit, holding 500-microns for 10 minutes without any gauge movement indicates a relatively leak-free system, according to Appler.  If the system moves up to 2,000-microns and holds there, it indicates moisture   remains in the system and steps 1 through 5 must be repeated. If it surpasses 2,000-microns, the system is leaking and may also potentially have moisture.

Chemical-Based Drying Agent Additives

"Triple evacuations and liquid line driers, as critical and effective as they are, probably will never totally rid the system of all moisture, particularly in POE oil systems," said Appler, who performed a live demonstration in the classes showing residual moisture. "Therefore the right chemical drying agents will aid evacuations and driers in moisture removal and make a huge difference in your service success and billing time. But it's important to know the different types of chemical drying agents and how they work scientifically."            

Chemical driers fall under three main categories:  1) alcohols; 2) vinyltrimethoxySilanes; and 3) orthoformates.  These chemicals are distributed in the HVAC/R industry under many brands, all which have material safety data sheets (MSDS) listing their contents, according to Appler.

Alcohols: Several industry drying agents use methanol, ethanol, isoproponol  and other alcohol-based chemicals, according to Appler. They can either be poured from a bottle into an oil injector tool or a charging hose, or contained in syringe-type devices, as well as hydrocarbon-charged canisters.  They don't proactively remove the moisture, but in a reactionary strategy, they prevent it from forming ice crystals that can block TEV orifices or capillary tubes. The ice crystal prevention is the same strategy used in glycol systems.  Alcohols are a quick temporary fix for a problem, such as frozen TEV's in a walk-in cooler that can't be shut down for moisture removal because there's no alternative food storage, however the moisture remains in its H2O form and will eventually create acid and corrosion later on. Aside from modifying the freezing point, alcohols molecularly have no beneficial effect on the chemical reactions involving refrigeration system water removal.                      

VinyltrimethoxySilanes have been used solely as a drying agent in the automobile air conditioning industry. They are sold in a syringe tool or canisters using R-134a or a hydrocarbon as a propellant. VinyltrimethoxySilanes  are a reactive compound that doesn't remove water molecules, but instead reacts with the moisture to form globular, soft polymers that could collect particulates and potentially cause flow resistance and orifice restrictions.           

Orthoformates are a reactive chemical that actually breaks apart H2O molecularly into ethanol and menthol. "You might be asking yourself  what's the difference because both the alcohol-based and orthoformates chemical driers end up as an alcohol in the system, but the difference is the orthoformate system has eliminated water while the alcohol-based driers only mask it," said Appler. "Orthoformates, because of their high reactivity and aggressive nature toward water, eradicate H2O in a two-stage attack."            

Orthoformates can only be packaged in a vacuum-packed can, or else they would start working before applying them to a system. Once connected to the low side of an "off" system, the vacuum-packed can allows the system's refrigerant to charge the can then inject it safely into the system when the system is switched back on. This seamless transfer prevents the product from ever being exposed to atmosphere or a primary propellant.             

Therefore, only vacuum-packed orthoformates brands can claim a specific removal in drops of moisture just as liquid line drier manufacturer instructions claim.                                                

Driers
In-line driers are effective in capturing water, acid and particulates from refrigerant systems by adsorption and filtration, but it's important to understand that water itself is still in the system. Therefore its good practice to replace a liquid line drier every time a system is opened or where high operating temperature differentials are found on the drier. That's why the aforementioned hydrolytic chemical driers can take moisture eradication to the next level.

Micron Gauge Tips
Appler said using conventional manifold gauges instead of a micron gauge during evacuations is like trying to use a clock instead of a stopwatch for precision timing. Boiling moisture off during an evacuation occurs generally under  2,000-microns. Conventional manifold gauges only have dial numbering increments of vacuum 0 to 30-inches where one-inch mercury is equal to 25,400-microns. Therefore it's impossible to determine precisely when the 2,000-micron threshold and below is reached. An electronic micron gauge however has increments ranging from 750,000 down to a possible 0.5-microns or lower, thereby providing accurate measurement in relationship to boiling point of moisture.             

To lower the probability of acids, corrosion, waxing and leaks while increasing the longevity of a refrigeration system a combined effort of triple evacuations, liquid line drier replacement and true chemical driers should all be part of the service tech's moisture-fighting arsenal today, Appler said.

Source: Cliplight

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