Causes of Unstable High and Low Pressures in Refrigerated Air Dryers

Excessively High Discharge Pressure of Refrigerated Air Dryer
Causes of excessive discharge pressure for air-cooled units:
High ambient temperature or poor ventilation
Dust and dirt accumulated on the condenser surface
Overloaded refrigerated air dryer
Air ingress into the refrigerant system
Insufficient heat transfer area of the condenser
Low air volume of the cooling fan

Improper installation position of the refrigerated air dryer (e.g., close to heat sources, 

direct sunlight exposure, insufficient spacing between front and rear dryers)

Incorrect setting or failure of the fan control pressure switch
Blockage in refrigerant passages or components
Overcharged refrigerant, reducing the effective heat transfer area
Excessively Low Suction Pressure
Excessive cooling water flow or excessively low water temperature
Low ambient temperature
Improper setting or failure of the fan control pressure switch or automatic cooling water regulating valve
Undercharged refrigerant
Leakage points in refrigerant pipelines or components
Light load on the refrigerated air dryer

Generally speaking, slightly low condensing pressure has no major adverse impact on the operation of refrigerated air dryers and refrigeration systems. 

However, excessively low condensing pressure may lead to reduced evaporation pressure, frost formation inside the evaporator, and even liquid slugging of the compressor, which needs to be prevented.

Excessively High Evaporation Temperature
Evaporation temperature rises with increasing evaporation pressure. The causes of elevated evaporation pressure are as follows:
The load of the refrigerated air dryer exceeds the rated value
Low operating pressure of compressed air
Excessively high temperature of compressed air entering the dryer
Malfunctions in the refrigerant system, such as excessive opening of the expansion valve/bypass valve, overcharged refrigerant, and high pressure caused by poor heat dissipation of the condenser
Excessively Low Evaporation Temperature

Excessively low evaporation temperature manifests as evaporation pressure below the normal range. Excluding inherent defects from design and manufacturing 

(such as insufficient heat transfer area of the evaporator, over-sized compressor, or insufficient refrigerant charging of the system), the operational causes include:

Insufficient opening of the bypass valve
Light load on the refrigerated air dryer
Frosting on the evaporator surface hindering heat transfer
Excessive oil content in compressed air forming an oil fouling layer on the heat exchange surface and impairing heat transfer
Slow leakage in the refrigerant system