HFC-134a and moisture

Question: I understand that moisture is in a CFC-12 system, or any refrigerant containing chlorine, will slowly hydrolyze with the water and form hydrochloric acids.

Since the new alternative refrigerant, HFC-134a, has no chlorine, would a moist system be subject to the problems of acid, corrosion, sludging, and sludge? Besides, freeze-ups, what effect would water have on an HFC system?

-David Woods, Sonyea, NY

Answer: The question about the effect of water with refrigerants that do not contain chlorine is a good one. The picture is not entirely clear at present. But I believe there should be no relaxation in the effort to keep water out of the system. In addition to freezing at the lower temperatures, water (especially in combination with oxygen) can cause corrosion and sludging. If carbon dioxide from air is also present, it will dissolve in water forming a weak acid that could cause trouble. In natural oils (that is, oils recovered from the ground), compounds containing nitrogen or sulfur may also be present and could react with water to form undesirable impurities.

There is some evidence that with present refrigerants, water that is dissolved in the liquid phase of the refrigerant is less harmful than water that remains undissolved. I have no information on the solubility of water in HFC-134a. But I believe it would be far less than in CFC-12 or HCFC-22. In this case, systems should be at least as dry as and perhaps drier than present systems. Also, excess water is known to cause pinhole corrosion of aluminum.

Incidentally, there =way be some slight reaction of refrigerants such as CFC-12 directly with water to form hydrochloric acid, but I believe most of it comes through the oil. Under severe conditions of temperature, refrigerants containing chlorine may react with hydrocarbon oils to exchange chlorine for hydrogen atoms.

Thus, CFC-12, CCl2F2 + H-oil = Cl-oil

The chlorinated oil can then easily break down, forming hydrochloric acid and unsaturated oil. The unsaturated oil can polymerize, breakdown further or react with water to form sludge. The HCl will dissolve in free water forming an acidic solution that is much more corrosive than the dry gas.

-Dr Ralph Downing, consultant