What it is

On a modern supermarket, each refrigerated case (or lineup) is run by a case controller — a small networked computer at the fixture that controls refrigeration, defrost, fans, lights, and anti-sweat heaters, and reports back to a store-wide controller. The piece that replaces the old mechanical TXV is an electronic expansion valve (EEV): a motor-driven valve the controller positions precisely to maintain superheat. Instead of a spring, bulb, and diaphragm reacting mechanically, the controller measures superheat electronically and commands the valve to exactly the position it wants.

The payoff is tight, low, stable superheat (more coil used = more capacity and efficiency), fast and accurate defrost, and full visibility — the controller logs case temperature, superheat, and faults, and a manager (or you) can see every case from one screen.

How it works

The controller computes superheat in real time from two inputs at the coil:

  1. A pressure transducer on the evaporator (or suction) tells the controller the evaporator pressure, which it converts to saturated suction temperature for the refrigerant in software (it knows the refrigerant and its P-T relationship, including glide handling for blends).
  2. A temperature sensor at the coil outlet gives the actual vapor temperature leaving the coil.

Superheat = coil-outlet temperature − saturated suction temperature, calculated continuously. The controller then drives the EEV to hold superheat at its target.

The EEV is typically a stepper-motor valve: the controller sends it a number of steps to open or close, positioning the orifice precisely anywhere between fully shut and fully open. If measured superheat is above target (coil starving), the controller opens the valve more steps to feed more liquid. If superheat is below target (coil overfeeding, floodback risk), it closes the valve. Because it's positioning a motor to a commanded step count — not balancing spring forces — it can hold superheat lower and steadier than a TXV, and react faster.

The same controller usually:

  • Controls case temperature by modulating refrigeration / cycling the EEV closed and managing any electronic EPR (a second stepper for case-temperature/suction regulation).
  • Runs defrost on schedule or demand, terminates on a coil sensor, manages fan delay, and often closes the EEV to isolate the coil during defrost.
  • Drives fans, lights, and anti-sweat heaters, sometimes modulating anti-sweat based on humidity.
  • Networks to the store controller for setpoints, logging, alarms, and remote access.

EEV vs. TXV in one breath: a TXV is self-contained and mechanical — bulb senses outlet temp, internal pressure balances against spring + equalizer to set superheat, no electronics. An EEV is dumb on its own; the controller is the brain, measuring superheat from a transducer + sensor and commanding the stepper. Diagnose a TXV as a mechanical valve; diagnose an EEV as a controlled output (target vs. actual, inputs, drive, wiring).

In the field

  • Start at the controller, not the valve. Read the live values: case/product temperature, evaporator pressure (and the derived saturated temp), coil-outlet temperature, calculated superheat, EEV position (% or steps), and any active alarms. The controller already shows you superheat and what the valve is doing.
  • Validate the inputs before trusting the math. A bad pressure transducer or a mislocated/failed coil-outlet temperature sensor makes the controller's superheat number wrong — and it'll drive the valve to the wrong place chasing a lie. Check the sensors against your own gauge/thermometer at the coil.
  • Compare measured vs. commanded. If the controller commands the EEV wide open but superheat stays high, the valve isn't feeding (stuck stepper, drive fault, wiring, or upstream liquid/charge/solenoid problem). If it commands nearly closed but superheat is low/zero, the valve's leaking by or the math is off.
  • Check the EEV drive and wiring. A stepper that won't move (failed motor, broken drive output, bad harness) sits where it stalled. The controller may flag it; confirm the valve physically tracks commands.
  • Mind defrost interaction. The controller may park the EEV closed during defrost and reopen after with a fan delay. A case that won't refrigerate "after defrost" can be an EEV that didn't reopen or a defrost-termination/sequence fault.

Normal values & targets

  • Superheat target: EEVs are typically run at a lower, tighter superheat than a TXV would hold (the controller can manage close to the floodback edge safely) — often a modest single-digit-to-low-double-digit °F target at the coil outlet, set in the controller per case. Lower stable superheat = more coil used = more capacity.
  • EEV position: reported as % open or step count; it should modulate with load (more open under heavy load/after defrost, less open at light load). A valve pinned at 0% or 100% is a clue.
  • Saturated suction temperature: derived in software from the transducer; matches the case's target coil temperature for the product class (medium- vs. low-temp).
  • Case/product temperature: held at the product setpoint; the controller logs it for food-safety records.
  • Glide handling: for blend refrigerants, the controller uses the correct saturation reference (dew point for superheat) internally — no manual P-T column reading needed, but the controller must be set to the correct refrigerant.

Representative — exact targets live in the controller configuration; confirm against the equipment and the programmed refrigerant.

Common faults & what they mean

  • Controller shows high superheat, case warm, EEV commanded open — valve not feeding: stuck/failed stepper EEV, drive board output fault, broken wiring/connector, or an upstream problem (liquid-line solenoid closed, low charge, plugged drier, no liquid to the valve). The brain wants liquid; the valve isn't delivering.
  • Controller shows low/zero superheat, floodback risk, EEV commanded nearly closed — valve leaking by (won't seat), or the superheat calculation is wrong because a sensor/transducer is bad. Verify the inputs before condemning the valve.
  • Superheat reading looks impossible / case behaves opposite to the number — bad pressure transducer or coil-outlet temperature sensor, wrong refrigerant programmed, or a sensor on the wrong line. The controller drives the valve off bad data. Check sensors against real instruments.
  • EEV won't move / stuck — stepper motor, drive output, or harness fault; the valve stalls in place and the case can't track load. The controller often alarms it.
  • Case won't refrigerate after defrost — EEV didn't reopen, defrost-termination/sequence fault, or fan-delay/control problem in the controller. The refrigeration sequence didn't resume.
  • Whole lineup/section down or odd — could be the store controller, the network, power to the case controllers, or a shared suction/rack issue — not the individual EEV. Step up a level.

Tech tips & gotchas

  • The controller is the brain; the EEV is a dumb motor. Diagnose the system: target superheat vs. measured, the two input sensors, the commanded valve position vs. actual, and the drive/wiring. Don't "replace the valve" the way you'd swap a TXV before confirming the controller's inputs and outputs.
  • Garbage in, garbage out — validate the sensors. A bad transducer or coil-outlet sensor makes the calculated superheat a lie, and the controller will happily drive the valve to the wrong place chasing it. Check both inputs against your own gauge and thermometer before trusting the screen.
  • Compare commanded position to actual behavior. EEV commanded wide open + high superheat = valve/feed problem. EEV commanded nearly shut + low superheat = leak-by or bad math. The mismatch between command and result tells you which side is broken.
  • Confirm the programmed refrigerant. The controller derives saturated temperature from the transducer using the configured refrigerant. Wrong refrigerant in the config = wrong superheat math = wrong valve action, even with perfect sensors.
  • EEVs run lower superheat on purpose. Don't "correct" a low single-digit superheat to TXV numbers — the electronic control is designed to hold tighter and lower for efficiency. Judge it against the controller's target, not a mechanical-TXV habit.
  • After-defrost no-cool is a sequence problem. EEV reopen, defrost termination, and fan delay all live in the controller. When a case won't refrigerate right after a defrost, look at the sequence/controller, not the refrigeration cycle.
  • Step up a level for multi-case faults. One case misbehaving = that case controller/EEV/sensors. A whole section = store controller, network, power, or the rack/suction group. Don't chase one EEV for a system-wide symptom.

Safety / code notes

  • EEV and sensor work that opens the refrigerant circuit follows EPA Section 608 — recover, don't vent.
  • Case controllers, stepper drives, and sensor circuits are live low-voltage electronics — verify before working in the panel and don't force a stepper valve mechanically.
  • Product/case temperatures the controller logs support food-safety records under the applicable food code — preserve/verify them when servicing.
  • Anti-sweat heaters and defrost heaters driven by the controller are electrical loads — lock out and verify dead before servicing those circuits.