Question: Why are OEM liquid line dryers on large tonnage hvac units (25+) undersized? I had to replace the powerhead on one TXV (12.5 tons per ckt) and found the OEM drier capacity maximum was 5 tons. If I were to replace it with the proper capacity drier, it would be very tough because of the lack of space. Would a smaller capacity drier (exact size replacement) cause a restriction?

-James Sekich, Vernon Hills, Ill.

Answer: An OEM drier recommendation is normally different from a field replacement recommendation. For example, a drier manufacturer may recommend his drier for 15 tons of R-22 for an OEM installation, but only 7 ½ tons of R-22 for a field replacement. The difference in recommended tonnage is based on the moisture of the drier. Drier recommendations are based on two factors: drying capability and flow capacity.

OEMs believe that because of their dehydration procedures on self-contained units that no or very little drying is required of the drier. Field erected systems do require larger dryers because of their greater moisture pick up requirements. In the example given, the drier has a flow capacity of 23 tons of R-22 at a two-pound pressure drop. This flow capacity was the deciding factor in establishing the OEM drier recommendations.

An exact replacement drier in subject systems will not lower system capacity, but the moisture indicator should be examined several times after start-up to see if the system refrigerant is dry. The drier should be replaced until a safe moisture level is obtained.

-Paul Schwarz, marking manager, Henry Valve Co.