High Suction Pressure- Low Superheat (evaporator outlet)

Probable Cause:

Oversized expansion valve.

Pin and seat of expansion valve drawn, eroded, or held open by foreign material-resulting in liquid flood-back.

Ruptured diaphragm or bellows in a constant pressure (automatic) expansion valve, resulting in liquid flood-back.

External equalizer line plugged, or external equalizer connection capped without providing a new valve cage or body with an internal equalizer.

Moisture freezing valve in open position.

Leaking valve stem packing.

Valve superheat setting too low.

Leaking liquid line in suction heat exchanger.

Unit coming out of defrost.



Replace with the correct size expansion valve.

Clean or replace damaged parts, or replace valve.

Install an ALCO EK or STAS filter-drier to remove foreign material from the system.

Replace valve power assembly.

If external equalizer is plugged, repair or replace. Otherwise, replace with valve having
the correct equalizer.

Apply heat gun to valve to melt ice.

Install an ALCO EK or ST AS filter-drier to insure a moisture-free system.

Replace TEV, or replace the cage in ALCO’s take-a-part series thermo valve.

Increase valve superheat setting to desired level (clockwise rotation of adjustment stem).

Liquid to suction heat exchanger defective (may not be needed, review requirements).

Normal, let the system balance.


NOTE: On a multi-evaporator system, the overfeeding of anyone of the valves can cause a high common
suction pressure-assuming all EPRs are wide open.