What do KE2 Evaporator Efficiency (KE2 Evap) alarms mean?
Short answer: the KE2 Evap scrolls its alarms in plain words, and the LED beside the readout tells you how serious it is. Yellow is an advisory alarm — the controller keeps running. Red is critical — the controller turns the system off to prevent compressor damage. If the auxiliary relay is set up as an alarm relay it switches too, and an internet-connected controller can e-mail or text the alarm.
Which machines use it?
The KE2 Evaporator Efficiency (KE2 Evap) from KE2 Therm is an aftermarket and OEM evaporator controller found on walk-in coolers and freezers of nearly any box brand — it's one of the most common retrofit controls in the country, often installed to add demand defrost and remote monitoring to an existing walk-in. If your evaporator has a small KE2 display that scrolls text alarms in plain words (HIGH AIR TEMP, DOOR SWITCH, EXCESS DEFROST) rather than cryptic codes, this is it. A yellow LED means a non-critical alarm with the system still running; a red LED is critical. Practical tip: the VARIABLES menu shows live sensor readings — a temperature of -87 means an unplugged sensor, 180+ means a shorted one.
How do you read and clear the display?
Every alarm has a matching entry in the VARIABLES menu with more information — room temperature, coil temperature, suction temperature and pressure, valve % open. KE2 also warns that many alarms are the result of incorrect wiring of the controller, sensors or valve, so every corrective action should include a wiring and installation check.
How do you enter the parameter menu?
The KE2 Evap's four-character display normally shows room temperature, defrost, or an alarm. The menus sit in columns beside it, and the arrow keys move between them; the VARIABLES column holds the live sensor readings and relay states that every alarm in the table below tells you to check. BACK steps up one level, and two or three presses return to the main menu or the room-temperature reading.
Changing a setting: navigate to it, press and hold ENTER for 3 seconds until the display blinks, change the value with the arrows, then press and hold ENTER for 3 seconds again to save.
Passwords: the controller prompts for one whenever you reach a set point you don't have rights to. The User password (1111) unlocks only the ROOM TEMP set point. The Installer password (2222) is needed for the SETPOINTS menu and for MANUAL control — which is also where a manual defrost is started. KE2 publishes these defaults in the quick-start guide; anyone who has changed them on your unit should have left a record.
First power-up: the controller runs an Introduction Mode that asks for ROOM TEMP, then DEFROST TYPE (electric, hot gas or air), then VALVE TYPE (mechanical, a defined EEV, or custom — an EEV adds a REFRIGERANT prompt), then whether KE2 Smart Access is enabled. Those are the only set points needed to start controlling a single evaporator, and a controller that still has the wrong DEFROST TYPE or VALVE TYPE from a rushed install is a common root of the defrost and superheat alarms below.
Every KE2 Evaporator Efficiency code at a glance
| Code | What it means |
|---|---|
| HIGH AIR TEMP | Room air temperature too warm |
| LOW AIR TEMP | Room air temperature too cold |
| EXCESS DEFROST | Too many defrost cycles |
| DEFR TERM ON TIME | Defrost ended on time instead of temperature |
| DOOR SWITCH | Door open alarm |
| T1 / T2 / T3 / T4 SENSOR | Temperature sensor failed (suction, air, coil, or aux) |
| HIGH SUPERHEAT | High superheat (EEV systems only) |
| LOW SUPERHEAT | Low superheat |
| PRESSURE SENSOR | Suction pressure transducer fault (critical) |
| COMMUNICATION ERROR | Bonded controllers lost communication |
| EXT ALARM | External device alarm passed through |
| Blank display (no lights) | No display or lights on controller |
| INTRO | INTRO displayed with all LEDs flashing — the controller isn't operational until it has been configured (KE2 bulletins N.1.1 / Q.1.3) status |
| NO ALARM | An alarm condition has been corrected; shown for about 10 minutes or until BACK is pressed status |
| E-MAIL FAILURE | KE2 SmartAccess only: the controller couldn't send an alarm e-mail — check the e-mail server settings message |
| ACCESS DENIED | KE2 SmartAccess only: site name or password not accepted (both are case-sensitive) message |
| Controller Communication Failure | KE2 SmartAccess only: the controller has stopped communicating with KE2's server — check the local network and internet connection message |
12 codes link to a full section below. The other 5 are listed as the manufacturer's manual gives them. Every row comes from the manual cited at the end of this page.
What does each code mean — and what should you do?
HIGH AIR TEMP — Room air temperature too warm
Air temperature has stayed above the setpoint plus the high-temp alarm offset (factory default 10°F over setpoint) for the alarm delay time (default 60 minutes). Yellow LED is lit and the system keeps running; this alarm is not triggered during defrost.
What causes it:
- Door propped open for loading, unloading, or inventory — humid air loads the box
- Heavy frost or ice on the evaporator coil
- Evaporator fans not all spinning
- Condensing unit not running, or its coil and airflow choked with debris
- Low refrigerant charge or a failed compressor — the not-DIY end of the list
Can staff fix it? Often. The system is still running (yellow LED, not a shutdown), and doors, coil ice, fan checks, and condenser airflow are all staff territory. If the box won't pull down after those, stop.
What to check, in order:
- Check whether the door was propped open for loading, unloading, or inventory, and make sure it is fully closed and sealing
- Look at the evaporator coil inside the box for heavy frost or ice buildup
- Verify all evaporator fans are spinning
- Confirm the condensing unit outside is running and its coil and airflow are clear of debris
Why it takes a technician: The remaining causes — low charge or a failed compressor — are sealed-system work: gauges, refrigerant handling, EPA Section 608 certification. And a box that can't reach temperature is quietly spoiling product the whole time.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
LOW AIR TEMP — Room air temperature too cold
Air temperature has been below the setpoint by the low-temp alarm offset (factory default 4°F below setpoint) for the alarm delay time (default 10 minutes). Yellow LED is lit and the system continues to run.
What causes it:
- The setpoint or the low-temp alarm offset/delay was changed
- The room genuinely overcooling — KE2 points at a leaking liquid line solenoid or a misadjusted low-pressure control
- A reading blip that clears itself once temperature returns to range
Can staff fix it? Partially. Confirm the real room temperature with a separate thermometer, check the settings weren't changed, and see if the alarm clears on its own. Genuine overcooling is not staff-fixable.
What to check, in order:
- Check the actual room temperature with a separate thermometer to confirm the reading
- Verify the setpoint and the low-temp alarm offset/delay were not accidentally changed
- Note whether the alarm clears on its own once temperature returns to range
Why it takes a technician: A leaking liquid line solenoid or a low-pressure control that needs adjustment are refrigerant-circuit components — gauge work under EPA Section 608. In a cooler, overcooling freezes product, so don't sit on a repeating alarm.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
EXCESS DEFROST — Too many defrost cycles
The controller counted 32 defrosts within 48 hours. It automatically forces Defrost Mode to a fixed schedule (default 5 per day) and keeps running with the yellow LED lit. KE2 notes the most common cause is coil sensor placement too close to a defrost heater, ending defrosts too early.
What causes it:
- Coil sensor mounted too close to a defrost heater, ending defrosts too early — KE2's most common cause
- The controller counted 32 defrosts in 48 hours and forced itself onto a fixed schedule as a protective fallback
- On air-defrost coolers, a room setpoint set below 36°F
Can staff fix it? Mostly no. Staff can note the alarm, check the coil for ice, and verify an air-defrost cooler isn't set below 36°F. The controller has already protected itself by switching to a fixed schedule.
What to check, in order:
- Note the alarm and current room temperature for the service tech
- Check the evaporator coil for visible ice buildup
- For coolers using air defrost, confirm the room setpoint is not set below 36°F
Why it takes a technician: Relocating the coil sensor, testing heaters and the solenoid valve, and returning Defrost Mode to Demand after the root cause is fixed are all inside-the-unit service tasks — heater testing is live electrical work.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
DEFR TERM ON TIME — Defrost ended on time instead of temperature
The coil failed to reach the defrost termination temperature during two consecutive defrost cycles, so defrost ended on the time limit instead. Often points to failed defrost heaters, an iced coil, or a door left open. Yellow LED is lit; the system keeps running.
What causes it:
- Failed defrost heaters, so the coil never reaches termination temperature
- A coil so iced over that defrost can't finish the job in the time allowed
- A door left open for long stretches, loading the coil with frost faster than defrost clears it
- On air-defrost coolers, a room setpoint below 36°F
Can staff fix it? Partially. Check for heavy coil ice, make sure the door isn't living propped-open, and verify the setpoint on air-defrost coolers. A heavily iced coil or a repeating alarm ends the DIY portion.
What to check, in order:
- Check the evaporator coil for heavy ice
- Verify the door has not been left open for extended periods
- For air-defrost coolers, confirm the room setpoint is not below 36°F
Why it takes a technician: Testing defrost heaters and solenoid valves is live electrical work on heating elements — exactly the kind of testing that belongs to a technician, before the iced coil takes the box over temperature.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
DOOR SWITCH — Door open alarm
The door switch input shows the door open past the Door Alarm Delay time while room temperature is 5°F above setpoint. Indicates a door left open, a misaligned door switch, or a switch wiring/configuration problem.
What causes it:
- The door genuinely left open past the delay while the room ran 5°F over setpoint
- A door gasket damaged or iced so the door never fully seals
- The two-piece magnetic switch knocked out of alignment
- Switch wiring or digital-input configuration problem
Can staff fix it? Usually. Close and latch the door, check the gasket, and line the two magnetic switch halves back up — then wait out the delay and see if it clears. Most DOOR SWITCH alarms end there.
What to check, in order:
- Verify the door is fully closed and latching, and check the gasket for damage or ice
- Look at the two-piece magnetic door switch — make sure both halves line up and neither has been knocked loose
- Close the door and see if the alarm clears after the delay time
Why it takes a technician: If the alarm stays on with the door closed and the switch aligned, someone needs to test switch continuity with a meter and check the controller's digital-input settings — service-level electrical and configuration work.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
T1 / T2 / T3 / T4 SENSOR — Temperature sensor failed (suction, air, coil, or aux)
The named temperature sensor is open, shorted, or not connected. In the VARIABLES menu a reading of -87 means open/disconnected and 180+ means shorted. Yellow LED is lit and the system keeps running.
What causes it:
- The named sensor open or unplugged — a VARIABLES reading of -87 is the giveaway
- The named sensor shorted — a reading of 180+ points there
- A sensor wire damaged, pinched, or iced over inside the box
Can staff fix it? Diagnosis yes, repair no. Staff can read which sensor is named in the scrolling text, pull its VARIABLES value (-87 open, 180+ shorted), and eyeball the wire for damage. The system keeps running meanwhile — yellow LED, not a shutdown.
What to check, in order:
- Note which sensor is named in the scrolling alarm text
- Check the VARIABLES menu reading: -87 = open or unplugged, 180+ = shorted
- Look for an obviously damaged, pinched, or iced-over sensor wire inside the box
- Record the readings for the service tech
Why it takes a technician: Confirming the failure means testing sensor resistance against KE2's temperature/ohm table and then replacing the sensor — or the controller if the input itself is bad. That's meter work a technician should do.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
HIGH SUPERHEAT — High superheat (EEV systems only)
Only on systems with an electric expansion valve: superheat has run 2°F above setpoint for 90 minutes with the valve at least 95% open. Commonly indicates low refrigerant charge or a valve problem. Yellow LED lit; system keeps running.
What causes it:
- Low refrigerant charge — the common culprit when the valve has been ≥95% open for 90 minutes and superheat still runs high
- An electric expansion valve problem
- A dirty or airflow-blocked condensing unit coil making the system work short-handed
Can staff fix it? Barely. Clearing debris off the condensing unit coil is the one useful staff move. Everything else on this alarm is refrigerant-side — note the alarm, room temperature, and duration, and make the call.
What to check, in order:
- Note the alarm, room temperature, and how long it has been active
- Check the condensing unit coil for dirt or blocked airflow and clear any debris
- Do not attempt refrigerant-side checks
Why it takes a technician: Checking suction pressure, refrigerant charge, and valve operation takes gauges on the sealed system, which is EPA Section 608 certified work by law. Low charge also usually means a leak that must be found, not just topped off.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
LOW SUPERHEAT — Low superheat
Superheat has been below 3°F for 5 minutes with the valve less than 10% open. KE2 says the most common cause is the compressor failing to start — often a low-pressure control switch that was never field-set, especially as outdoor temperatures drop in fall.
What causes it:
- The compressor not starting — KE2's most common cause, often a low-pressure control switch that was never field-set
- Falling outdoor temperatures in autumn exposing that never-set control
- Evaporator fans off or a service switch left off
- Excessive frost on the coil
Can staff fix it? Diagnosis only. Staff can confirm whether the outdoor compressor is actually running, check the evaporator fans and service switch, and look for heavy frost. Setting pressure controls is explicitly not a DIY item.
What to check, in order:
- Confirm the condensing unit compressor is actually running (listen/look at the outdoor unit)
- Verify all evaporator fans are running and no service switch was left off
- Check the coil for excessive frost on the air-entering and air-exiting sides
Why it takes a technician: Setting the low-pressure cut-in/cut-out control is the installing contractor's job, done with gauges on the refrigerant circuit. Left wrong, the system will keep dropping out every time the weather turns.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
PRESSURE SENSOR — Suction pressure transducer fault (critical)
Only active when an electric expansion valve is selected: the suction pressure sensor is shorted, open, out of range, or miswired. This is a red-LED critical alarm and the controller shuts the system down to protect the compressor.
What causes it:
- The suction pressure transducer shorted, open, out of range, or miswired
- The controller has shut the whole system down to protect the compressor — this is the red-LED critical alarm
- A cable unplugged or visibly damaged at the transducer
Can staff fix it? No, and it's urgent: refrigeration is OFF and the box is warming. Staff can check the transducer cable is plugged in and undamaged, then focus on moving product if the tech can't come fast.
What to check, in order:
- Treat this as urgent — the refrigeration system is off and box temperature will rise
- Check that the transducer cable is plugged in and not visibly damaged
- Move product to another cooler if the tech cannot come quickly
Why it takes a technician: Verifying transducer voltage and pressure readings requires meters and gauges on the refrigerant side — EPA Section 608 certified work. With the system down, product loss urgency makes this an immediate call, not a same-week one.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
COMMUNICATION ERROR — Bonded controllers lost communication
On multi-evaporator systems with bonded controllers, this KE2 Evap failed to communicate with its bonded partners. Most commonly a local network issue (cables, switches, or a router-changed IP address). Yellow LED lit; system keeps running.
What causes it:
- Ethernet cables between bonded controllers or the network switch unplugged or failed
- The network switch without power
- A router reassigning a controller's IP address — KE2's classic local-network cause
Can staff fix it? Often, yes — this is the rare alarm that's more IT than refrigeration. Reseat the Ethernet cables, confirm the switch has power, and power-cycle the switch. Cooling continues the whole time (yellow LED).
What to check, in order:
- Check that the Ethernet cables between controllers and any network switch are plugged in
- Verify the network switch has power
- Power-cycle the network switch if one is used
Why it takes a technician: If reseating cables doesn't clear it, the controllers may need re-bonding — a KE2 service procedure your refrigeration or controls contractor performs, not a menu item for staff.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
EXT ALARM — External device alarm passed through
A third-party device wired to a digital input (for example a condensate pan overflow float switch) has tripped. The controller displays and forwards the alarm but refrigeration control continues normally.
What causes it:
- A third-party device wired to the digital input has tripped — most commonly a condensate pan overflow float switch
- A clogged drain line backing water up into the pan until the float lifts
- Refrigeration control itself is unaffected; the controller is only passing the message along
Can staff fix it? Frequently. If a drain-pan float is the connected device, checking the pan for standing water and clearing a visible blockage at the drain outlet is well within staff ability, and cooling never stopped.
What to check, in order:
- Identify which external device is wired to the controller (often a drain pan float switch)
- Check the drain pan for standing water or a clogged drain line if a float switch is installed
- Clear any visible blockage at the drain outlet
Why it takes a technician: If the device keeps tripping, or nobody on site knows what is actually wired to that input, a technician needs to trace the input and fix the underlying device — repeated pan overflows, for example, mean a drain problem that will eventually leak into the box.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
Blank display (no lights) — No display or lights on controller
Not a coded alarm, but the controller is not operational if the display is blank. KE2 lists incoming power, voltage jumper settings, the board fuse, or power injected through the RJ45 port (PoE) as causes.
What causes it:
- No incoming power — breaker off on the evaporator/controller circuit
- The controller plugged into a Power-over-Ethernet switch port — PoE can blank the display
- Voltage jumper settings or a blown board fuse, per KE2's list
Can staff fix it? Sometimes. Check the breaker, and if the controller is networked, make sure it isn't on a PoE switch port — that one is a genuine plug-it-elsewhere fix. Also note whether fans and refrigeration are still running.
What to check, in order:
- Check the breaker feeding the evaporator/controller circuit
- If the controller is networked, confirm it is not plugged into a Power-over-Ethernet switch port (PoE can blank the display)
- Note whether the evaporator fans and refrigeration are still running
Why it takes a technician: If the breaker is on and the display is still dark, what's left is checking voltage jumpers and the board fuse — live electrical work inside the controller that belongs to a technician.
Source: KE2 Therm Solutions — KE2 Evaporator Efficiency — alarm troubleshooting guide (Q.1.17, August 2017 (KE2's document, hosted by OEM partner Krack))
How do you diagnose a KE2 Evaporator Efficiency alarm, step by step?
- Yellow or red? Yellow means you have time to diagnose with the system running; red means the system is off and product temperature is rising.
- Open VARIABLES and read the value KE2 lists for that alarm.
- Sensor alarms decode instantly: a sensor reading of −87 means it's open or not connected; 180 or higher means it's shorted.
- Then measure it. Unplug the sensor and compare its resistance with KE2's table — about 2,000 Ω at 77 °F, 5,114 Ω at 32 °F, 12,110 Ω at −4 °F. If it has been extended, check the splice. If it still looks right, swap in a sensor that isn't alarming: if the controller can't read a known-good sensor either, the controller is the problem.
- LOW SUPERHEAT usually means the compressor didn't start. KE2's most common cause is a low-pressure control that was never set in the field — it is the installer's job, not the factory's. If the alarm comes and goes, and especially if it shows up in the fall as outdoor temperatures drop, suspect this first.
- HIGH SUPERHEAT (valve systems only) triggers when superheat has been 2 °F above setpoint for 90 minutes with the valve at least 95 % open — check suction pressure, the refrigerant setting and valve operation; the system may be short of refrigerant.
- PRESSURE SENSOR (red, system off): check the connector position, 5 V DC between the black and red wires, and the signal on green; a transducer removed from the system should read about 0 psig.
- No display at all isn't an alarm, but the controller isn't running: check incoming power, the voltage jumpers for your supply and the board fuse.
Which parts are usually involved?
| Part | Codes that point to it | Note |
|---|---|---|
| T1 suction, T2 air, T3 coil and T4 auxiliary temperature sensors | T1 / T2 / T3 / T4 SENSOR, HIGH AIR TEMP, LOW AIR TEMP | KE2's curve (about 2,000 Ω at 77 °F) differs from Heatcraft's (10,000 Ω at 77 °F), so sensors aren't interchangeable between brands. |
| Suction pressure transducer (EEV systems) | PRESSURE SENSOR, HIGH SUPERHEAT, LOW SUPERHEAT | |
| Electric expansion valve | HIGH SUPERHEAT, LOW SUPERHEAT | |
| Low-pressure control and liquid line solenoid | LOW SUPERHEAT | |
| Defrost heaters and coil sensor | EXCESS DEFROST, DEFR TERM ON TIME | |
| Door switch (digital input 1) | DOOR SWITCH | |
| Device on the external alarm input | EXT ALARM | |
| Network cables and switches (bonded controllers) | COMMUNICATION ERROR | |
| Incoming power, voltage jumpers and board fuse | Blank display (no lights) |
What refrigeration is behind these codes?
Every code here is the controller reporting a reading from the refrigeration system. The background is explained once, for every controller on this site: what superheat is and why controllers alarm on it; how defrost works and what goes wrong; how a controller holds temperature — and how its sensors are tested.
If it does come to a service call and you're in Nashville, TN or Birmingham, AL, we maintain independently compiled lists of local companies that service walk-in coolers — real businesses with verified contact information, none of whom paid to be listed.