Kolpak Walk-In Error Code EE: Program Failure

What does Kolpak error code EE mean?

The A421 keeps its operating program in memory, including the setpoint and the rules for switching the compressor. At power-up, and while running, it verifies that this program is intact. If the memory is lost or damaged, the control cannot trust its own instructions, so it turns the output off and shows EE. With the output off the compressor does not run, so the walk-in is not cooling and food is at risk as the box warms. The display shows EE until the control is reset or replaced. This applies to Polar-Pak drop-in systems such as the PCA050BT2, PCE075BT3 and PFE100BT3. A power surge or a brownout can corrupt memory, and that is why the manual points at a reset first. If a reset holds, the box returns to normal and the cause may have been a one-time event. If EE returns, the control itself is the likely repair.

Affected models and control systems

Kolpak Polar-Pak drop-in systems with the Johnson Controls A421 electronic temperature control, such as the PCA050BT2, PCE075BT3 and PFE100BT3. Other controls use different displays.

Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.

What you may notice

• EE on the control display
• Compressor not running
• Box temperature rising
• Control does not respond to setpoint changes

Possible causes

Listed in Kolpak's documentation

• Program memory of the A421 lost or damaged
• Output turned off by the control

Other likely causes — what usually sits behind error code EE on this control. A technician confirms which one it is before any part is replaced.

• Power surge or brownout that corrupted the control memory
• Unstable supply to the control
• Aging A421 control that cannot hold its program
• Loose supply wiring to the control

Safe checks before calling for service

How a technician diagnoses error code EE

1. Check the box temperature and confirm the compressor is off.
2. Verify the supply voltage to the control and the system.
3. Perform the manual's MENU reset and watch whether EE returns.
4. Reconfigure the setpoint and settings if the reset restores operation.
5. Replace the A421 control if EE persists.

Technical reference

Document

POLAR-PAK Drop-In Refrigeration System IOM, P/N 550002878-14 (4/25), Troubleshooting table (Johnson Controls A421)

Edition

Part Number: 550002878-14 4/25

Models / control

Johnson Controls A421 electronic temperature control (Polar-Pak drop-in systems)

Section

Troubleshooting - A421 fault code table, p. 19

Checked

October 2026

We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.