Ozone-safe, 100% chlorine free, R-134a refrigerant as standard: Donaldson uses R-134a refrigerant in all refrigerated compressed air dryers as standard. R-134a has become the industry’s choice as the preferred refrigerant because of its ozone depletion factor of 0.0 and low global warming potential. R-134a is a one-blend refrigerant and, therefore, consistent in performance (no temperature glide) and easy to service (no mixture of different refrigerants).