Fluctuating Suction Pressure

Probable Cause:

Incorrect superheat adjustment.

Improper remote bulb location or installation.

“Flood-back” of liquid refrigerant caused by poorly designed liquid distribution device, or uneven evaporator loading.

External equalizer lines tapped at a common point although there is more than one expansion valve on the same system.

Faulty condensing water regulator.

Evaporative condenser cycling, causing a radical change in pressure difference across the expansion valve.

Cycling of blowers or brine pumps.

Restricted external equalizer line.

Condenser fan cycling based on power switch settings.

Oversized TEV.

Faulty or oversized EPR valve.



See “Measuring Superheat.”

Clamp remote bulb to free draining suction line.
Clean suction line thoroughly before clamping bulb in place.

Replace faulty distributor (must be properly sized).

If evaporator loading is uneven, install proper load distribution devices to balance air velocity evenly over evaporator coils.

Each valve must have its own separate equalizer line going directly to its own separate evaporator outlet to insure proper operational response of each individual.

Replace condensing water regulator.

Check spray nozzles, coil surface, control circuits, thermostat overloads, etc.

Repair or replace any defective equipment.

Clean clogged nozzles, coil surface, etc.

Clear blockage or replace equalizer line.
Normal for fan cycling operation. In order to eliminate, base fan cycling on ambient air temperature with pressure override. Or, use variable fan sped or flooded head pressure control system but not both together.
Replace with proper size.

Repair or resize and install EPR valve.