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MrCool E1 on a DIY E Star 3rd Gen: communication error

By How House Works EditorialBased on MrCool manualsChecked against sources Updated

MrCool display

E1

“Indoor / outdoor units communication error **”

DIY E Star 3rd Gen · DIY E Star 3rd Gen Installation & Owner's Manual, p. 39
Owner checks, then technician

Operation LED 2 flashes, timer LED off. The ** note says the wire colors of this series may differ from previous models, other series and general conventions, and that all wiring must follow the wiring diagrams in Section 7. Later DIY manuals use EL 01 for a communication error between the units. Letter codes are not shared safely across documents: the Advantage 4th Gen service manual's letter table also has E1 as an indoor/outdoor communication error (Advantage 4th Gen Service Manual, Troubleshooting p. 4), but other letters such as P6 change meaning.

What it means

E1 is a DIY E Star 3rd Gen code. In that manual’s error table it reads “Indoor / outdoor units communication error **”, shown with 2 flashes of the operation LED and the timer LED off DIY E Star 3rd Gen Installation & Owner’s Manual, p. 39.

The two asterisks point to a note on wiring: the wire colors of this series may differ from previous models, other series and general wiring conventions, all wiring must follow the wiring diagrams in Section 7 (Fig. 7.1) and the associated images, and wires and terminals are numbered to match DIY E Star 3rd Gen Installation & Owner’s Manual, p. 39. The manual gives no other description of the fault, and no 3rd Gen E Star service manual was found among MrCool’s published documents.

Check your series before you use this page. Letter codes like E1 appear in the 3rd Gen E Star manual and in the Advantage 4th Gen service manual. The DIY 4th and 5th Gen manuals show a communication error between the units as EL 01. Other letter codes change meaning from one document to the next; P6 has three.

Check these first

The 3rd Gen manual gives one procedure for any error code DIY E Star 3rd Gen Installation & Owner’s Manual, p. 38:

  1. Wait about 10 minutes. The manual says the unit may stop or keep running in a safety condition, depending on the model, and the fault may clear by itself.
  2. If it does not, disconnect the power and reconnect it.
  3. If the problem is still there after power is restored, disconnect the power and contact the nearest customer service center. The manual’s note asks you to give a qualified service professional the details of the malfunction and the unit’s model number.

After a sudden power on-off, the protection circuit keeps the compressor from running for roughly 3 minutes DIY E Star 3rd Gen Installation & Owner’s Manual, p. 37.

The procedure page also lists conditions the manual says not to correct yourself: a signal or power cable that is damaged or abnormally warm, a burning odor, loud or abnormal sounds, a power fuse or circuit breaker that trips frequently, and water or other objects falling into or out of the unit DIY E Star 3rd Gen Installation & Owner’s Manual, p. 38.

When to call a licensed technician

Checking the wiring between the units, and the boards at each end, is technician work. The wiring note above is the 3rd Gen manual’s only guidance on this code DIY E Star 3rd Gen Installation & Owner’s Manual, p. 39.

For EL 01 on 5th Gen DIY units, the service manual starts with a power-off and a restart 2 minutes later, then checks the wiring between the indoor and outdoor units, the communication line and the indoor and outdoor boards DIY 5th Gen Single-Zone Service Manual, p. 56. The Advantage 4th Gen service manual’s E1/EL 01 section describes the fault the same way and lists the indoor PCB, the outdoor PCB and a short-circuited component as parts to prepare Advantage 4th Gen Service Manual, Troubleshooting p. 20. Neither manual is written for the 3rd Gen E Star.

The 3rd Gen manual says: “ALL WIRING MUST BE INSTALLED BY A LICENSED ELECTRICIAN AND COMPLY WITH LOCAL, STATE, AND NATIONAL ELECTRICAL CODES.” DIY E Star 3rd Gen Installation & Owner’s Manual, p. 34. It also opens with a disclaimer that you assume the risk when handling materials containing refrigerants under pressure DIY E Star 3rd Gen Installation & Owner’s Manual, p. 1.

Notes for different models

  • Advantage 4th Gen: the service manual’s letter-code table also has E1, “Indoor / outdoor unit communication error”, with 2 operation lamp flashes and the timer lamp off, and the section is headed “E1/EL 01” Advantage 4th Gen Service Manual, Troubleshooting pp. 4, 20.
  • DIY 4th Gen E Star, multi-zone and cassette: the same lamp pattern goes with code EL 01 DIY E Star 4th Gen Installation & Owner’s Manual, p. 41.

Related MrCool codes

  • EL 01 “IDU & ODU Communication Error”
  • EH 0B “IDU Main Control Board & Display Board Communication Error”
  • PC 40 “Communication Error between Outdoor Main Chip & Compressor-Driven Chip”

See also

Other ductless mini-splits: Daikin, Fujitsu, Mitsubishi Electric

All MrCool codes

MrCool is a trademark of its owner. How House Works is not affiliated with or endorsed by MrCool.

Sources

  1. MRCOOL. DIY 5th Gen Single-Zone Service Manual. Version Date April 20, 2026; file suffix -01; no document number printed; same models as the owner's manual. Accessed Oct 13, 2026.
  2. MRCOOL. DIY E Star 4th Gen Installation & Owner's Manual. Version Date 03-21-23; file suffix -01; no document number printed. Not listed on MrCool's documentation page on 2026-10-13; the file is on MrCool's own file host. It prints the same Version Date as the 3rd Gen E Star manual.. Accessed Oct 13, 2026.
  3. MRCOOL. Advantage 4th Gen Service Manual. Version Date 7/06/22; file suffix -01; cover title Advantage Series Air Handler & Condenser Service Manual; pages are numbered within sections, cited as printed (Troubleshooting 5). It prints two lamp tables: one with letter codes (E1, P4, P6 and so on) and one with EH, EL, EC and PC codes. This table uses the second.. Accessed Oct 13, 2026.
  4. MRCOOL. DIY E Star 3rd Gen Installation & Owner's Manual. Version Date 03-21-23; file suffix -01; no document number printed. Not listed on MrCool's documentation page on 2026-10-13; the file is on MrCool's own file host. The code table's text layer is scrambled, so it was read from the page image.. Accessed Oct 13, 2026.