How House Works

MrCool EL 01: indoor and outdoor units not communicating

By How House Works EditorialBased on MrCool manualsChecked against sources Updated

MrCool display

EL 01

“IDU & ODU Communication Error”

DIY 5th Gen, DIY Select, Easy Pro, Advantage 5th Gen, DIY 5th Gen Multi-Zone, DIY 5th Gen Cassette, DIY Hybrid Air Handler, Olympus Ducted · DIY 5th Gen owner's p. 39; Select owner's p. 41; Easy Pro owner's p. 41; Advantage 5th Gen owner's p. 46; DIY 5th Gen multi-zone owner's p. 48; DIY 5th Gen cassette owner's p. 45; Hybrid air handler owner's p. 56; Olympus ducted owner's p. 43
Owner checks, then technician

Also in the outdoor board tables (DIY 5th Gen Single-Zone Installation & Owner's Manual, p. 40). Service manual: the indoor unit cannot communicate with the outdoor unit (DIY 5th Gen Single-Zone Service Manual, p. 56). The DIY E Star 3rd Gen manual lists a communication error between the units as E1.

What it means

EL 01 means the indoor unit cannot communicate with the outdoor unit DIY 5th Gen Single-Zone Service Manual, p. 56. The multi-zone service manuals give the condition: the indoor unit receives no feedback from the outdoor unit for 110 seconds, four times in a row DIY 5th Gen Multi-Zone Service Manual, p. 48; DIY 4th Gen Multi-Zone Troubleshooting & Solutions Guide, Troubleshooting p. 28.

The code is in both tables of the 5th Gen manuals, the indoor display and the outdoor board DIY 5th Gen Single-Zone Installation & Owner’s Manual, pp. 39–40. On 4th Gen units the operation lamp flashes twice with the timer lamp off, and the display shows EL 01 DIY E Star 4th Gen Installation & Owner’s Manual, p. 41. The DIY E Star 3rd Gen manual lists an indoor/outdoor communication error as E1.

Check these first

MrCool’s owner’s manuals give no steps for EL 01 itself. The procedure for any error code is:

  1. Wait about 10 minutes. The manual says the problem may resolve itself DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 38.
  2. If not, disconnect the power, connect it again and turn the unit on DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 38. It cannot be restarted within 3 minutes of being turned off DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 37.
  3. If EL 01 comes back, disconnect the power and contact MrCool. Give them your model number and describe what the unit did DIY 5th Gen Single-Zone Installation & Owner’s Manual, pp. 37–38.

Turn the unit off immediately if the wire is damaged or abnormally warm, you smell burning, or a fuse blows or the breaker trips frequently; the manual says not to fix these yourself and to contact an authorized service provider DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 37.

The DIY Select, Easy Pro, Advantage 5th Gen, cassette and Olympus manuals print the same wait-and-restart procedure DIY Select Installation & Owner’s Manual, p. 40; Easy Pro Installation & Owner’s Manual, p. 40; Advantage 5th Gen Installation & Owner’s Manual, p. 45; DIY 5th Gen Cassette Installation & Owner’s Manual, p. 44; Olympus Ducted Air Handler Installation & Owner’s Manual, p. 41. The 5th Gen multi-zone and hybrid air handler manuals do not; they say to contact a local dealer or MrCool customer service DIY 5th Gen Multi-Zone Installation & Owner’s Manual, p. 46; DIY Hybrid Air Handler Installation & Owner’s Manual, p. 54.

When to call a licensed technician

The DIY 5th Gen service manual’s check starts with a power-off and a restart 2 minutes later. If the code returns, it covers the wiring connection between the indoor and outdoor units, electrical checks of the communication line, the wiring from each terminal block to its board, the supply to the IPM board and high-voltage parts connected to the main board that may be short-circuited. The fixes it ends with are correcting the connection or changing wires, or replacing the indoor board, the outdoor board, the IPM board, a short-circuited part or the expansion valve coil DIY 5th Gen Single-Zone Service Manual, p. 56. The parts it lists to prepare are the indoor PCB, the outdoor PCB and a short-circuited component; the multi-zone manual adds the IPM module board and the reactor DIY 5th Gen Multi-Zone Service Manual, p. 48.

If you installed the system yourself, the interconnecting wiring is the first thing this check looks at. MrCool’s manual says electrical work must be completed by a qualified electrical technician DIY 5th Gen Single-Zone Installation & Owner’s Manual, p. 2, and the service manual warns that electricity remains in capacitors after the power is off DIY 5th Gen Single-Zone Service Manual, p. 35.

Notes for different models

  • 4th Gen E Star, multi-zone, cassette and Advantage: “Indoor / outdoor unit communication error.” DIY E Star 4th Gen Installation & Owner’s Manual, p. 41. The E Star and multi-zone manuals say “roughly 10 minutes” in the same procedure and add “DO NOT attempt these repairs yourself” DIY 4th Gen Multi-Zone Installation & Owner’s Manual, p. 49.
  • The Advantage 4th Gen service manual heads its section “E1/EL 01”: on that series the older letter-code table uses E1 for the same fault Advantage 4th Gen Service Manual, Troubleshooting pp. 4, 20.
  • Other communication codes point elsewhere: EH 0B is between the indoor main board and the display board, and PC 40 is between the outdoor main chip and the compressor-driven chip DIY 5th Gen Single-Zone Installation & Owner’s Manual, pp. 39–40.

Related MrCool codes

  • E1 “Indoor / outdoor units 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 Installation & Owner's Manual. Version Date August 5, 2026; file suffix -01; no document number printed. Cover title: DIY Series Single-Zone Mini-Split System, Installation & Owner's Manual. Accessed Oct 13, 2026.
  2. 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.
  3. MRCOOL. DIY Select Installation & Owner's Manual. Version Date August 5, 2026; no file suffix; no document number printed. Accessed Oct 13, 2026.
  4. MRCOOL. Easy Pro Installation & Owner's Manual. Version Date August 5, 2026; no file suffix; no document number printed. Cover title: MRCOOL DIY Easy Pro Mini-Split System. Accessed Oct 13, 2026.
  5. MRCOOL. Advantage 5th Gen Installation & Owner's Manual. Version Date September 19, 2025; file suffix -01; no document number printed. Accessed Oct 13, 2026.
  6. MRCOOL. DIY 5th Gen Multi-Zone Installation & Owner's Manual. Version Date January 8, 2026; file suffix -01; no document number printed. Its code table is titled “Error Display (Indoor Unit)” but lists outdoor unit codes.. Accessed Oct 13, 2026.
  7. MRCOOL. DIY 5th Gen Multi-Zone Service Manual. Version Date April 20, 2026; file suffix -01; no document number printed. Accessed Oct 13, 2026.
  8. MRCOOL. DIY 5th Gen Cassette Installation & Owner's Manual. Version Date December 02, 2025; file suffix -01; no document number printed. Cover title: DIY Series Outtasight One-Way Cassette. Accessed Oct 13, 2026.
  9. MRCOOL. DIY Hybrid Air Handler Installation & Owner's Manual. Version Date April 21, 2026; file suffix -01; no document number printed. Not linked from MrCool's documentation page on 2026-10-13; the file is on MrCool's own file host.. Accessed Oct 13, 2026.
  10. MRCOOL. Olympus Ducted Air Handler Installation & Owner's Manual. Version Date May 29, 2025; file suffix -01; no document number printed. Cover title: Olympus Series Mid-Static Ducted Air Handler. Accessed Oct 13, 2026.
  11. 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.
  12. MRCOOL. DIY 4th Gen Multi-Zone Installation & Owner's Manual. Version Date 06-06-2023; 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.. Accessed Oct 13, 2026.
  13. MRCOOL. DIY 4th Gen Multi-Zone Troubleshooting & Solutions Guide. Version Date 10-22-21; file suffix -01; pages are numbered within the Troubleshooting section, cited as printed (Troubleshooting 4). A technician document. MrCool's documentation page labels it the owner's manual for 4th Gen DIY.. Accessed Oct 13, 2026.
  14. 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.