I read an article today that said that modern AC units require a dryer built into them as HFC refrigerants like R-134a absorb water, whereas old Freon AC units did not require a dryer. Does this mean that AC units from the 50s did not dry out the air like modern ones do?
In: Physics
You’re confusing 2 things here. AC units capability to dehumidify and a refrigeration component known as a filter drier.
AC units, by design, are dehumidifiers. An older AC unit would’ve dehumidified just the same as an AC unit today. Possibly less efficiently but more or less the same. The fan passes air over a cold coil and heat is removed from the air, which causes any moisture in the conditioned air to condense.
Now a filter drier is a refrigeration component. Not to be confused with an air filter, the filter drier has nothing to do with drying the conditioned air, instead it deals with the refrigerant within the pipes.
For an AC unit to work, within the closed loop, you need to have pure refrigerant that follows a predictable and definite pressure and temperature relationship. When the pipes are sealed all air and moisture must be removed through the process of evacuation, pulling a vacuum. Previous refrigerants, CFCs and HCFCs, were somewhat forgiving and the oils they used were less hydroscopic. Filter driers were used but less frequently. With the shift to HFCs and polyester oil, which is significantly more hydroscopic, filter driers and more stringent evacuation procedures are necessary when adding refrigerant to systems. Really though, any time a closed system is opened for repair, the filter drier should be replaced regardless of the refrigerant type.
The filter drier is a refrigerant loop component that has a desiccant core and its purpose is to remove any additional moisture from a closed loop after refrigerant has been added during installation. It has nothing to do with the AC units dehumidification of the conditioned space.
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