AC Error Codes · Rheem
Rheem AC Error Codes: ICC Control Board Display Explained
Find your code, understand what it means, then run a guided diagnosis.
Error Code Finder
Look a code up against sourced manufacturer records. Codes we cannot source are not listed — a guessed meaning is worse than no meaning.
Rheem residential condensers report through the ICC (Integrated Control Center) board, and its display is unusual in one important way: several of the characters it shows are normal operating states, not faults. A 0 means standby, c and C mean first and second-stage cooling, and t means test mode. Faults are the numbered codes and the L-prefixed lockouts, which indicate a fault has repeated enough times for the board to stop trying.
How do Rheem ICC board codes work?
On a Rheem ICC board, 0, c, C and t are normal states — standby, first-stage cooling, second-stage cooling and test mode. Numbered codes are faults: 2 is a high-side fault, 3 is short cycling, 27 and 28 are low and high line voltage, and 30 is an open board fuse. An L prefix means a lockout — L4 is a locked rotor, and L21 and L29 indicate active low and high pressure trip protection.
Product families covered
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Residential split / packaged (ICC board)
Single-character and numeric displays read from the outdoor unit's control board.
Where the code is displayed — and why it matters
The same fault can be labelled differently depending on which display you read it from, so identify the display before looking the code up.
- ICC board display (outdoor unit)
- A single character or short number on the control board itself.
- Flashing display
- Flashing changes the meaning — a flashing c indicates a timer is active, and a flashing L21 or L29 indicates active trip protection.
Reading the Rheem ICC display
The format tells you whether you are looking at a state or a fault:
- 0 / c / C / t
- Normal operating states — standby, stage 1 cooling, stage 2 cooling, test mode
- Number
- A detected fault — pressure, voltage, airflow, sensor or control faults
- L + number
- A lockout — the fault repeated and the board stopped retrying
- d-codes
- Communicating-system data faults (d1, d3, D4, d8)
How the families differ
- Case matters: lower-case c is first-stage cooling and upper-case C is second-stage cooling.
- A lockout code is the escalated form of a fault — L6 and L7 mean the open start or run circuit fault occurred four times.
- Rheem's ductless mini-split codes were not isolated from the packaged and split condenser table in our source, so mini-split-specific codes are not published here.
Rheem ICC control board displays
Includes the normal operating states, because reading one of those as a fault is a common mistake with this board. Sourced from two independent technical references with matching entries.
| Code | What it reports | Applies to | Severity | Source |
|---|---|---|---|---|
| 0 | Indicates standby — no operation command | Residential split / packaged (ICC board) | Low | B |
| c | Indicates first-stage cooling active; flashing indicates an anti-short-cycle or minimum-run timer is active | Residential split / packaged (ICC board) | Low | B |
| C | Indicates second-stage cooling active; flashing indicates a timer is active | Residential split / packaged (ICC board) | Low | B |
| t | Indicates test mode | Residential split / packaged (ICC board) | Low | B |
| P | Indicates protector trip — a compressor command is present but no current is measured | Residential split / packaged (ICC board) | High | B |
| 1 | Indicates long run time — the compressor ran continuously for over 18 hours in cooling | Residential split / packaged (ICC board) | Moderate | B |
| 2 | Indicates high-side fault — the compressor limit opened four times within one call | Residential split / packaged (ICC board) | High | B |
| 3 | Indicates short cycling — each of the last four compressor cycles was under 3 minutes | Residential split / packaged (ICC board) | High | B |
| L4 | Indicates locked rotor — four consecutive protector trips, each under 15 seconds | Residential split / packaged (ICC board) | High | B |
| 5 | Indicates open circuit — no current in the start or run circuits despite an operation command | Residential split / packaged (ICC board) | High | B |
| 6 / L6 | Indicates compressor open start circuit (L6 indicates the fault repeated four times) | Residential split / packaged (ICC board) | High | B |
| 7 / L7 | Indicates compressor open run circuit (L7 indicates the fault repeated four times) | Residential split / packaged (ICC board) | High | B |
| 9 | Indicates low secondary voltage — below 18V AC at the R and C terminals | Residential split / packaged (ICC board) | Moderate | B |
| 21 / L21 | Indicates low-pressure control open; a flashing L21 indicates active low-pressure trip protection | Residential split / packaged (ICC board) | High | B |
| 27 | Indicates low or no line voltage fault | Residential split / packaged (ICC board) | High | B |
| 28 | Indicates high line voltage fault | Residential split / packaged (ICC board) | High | B |
| 29 / L29 | Indicates high-pressure control open; a flashing L29 indicates active high-pressure trip protection | Residential split / packaged (ICC board) | High | B |
| 30 | Indicates on-board fuse open | Residential split / packaged (ICC board) | High | B |
| 80 | Indicates low airflow — the indoor unit is not meeting the minimum airflow requirement | Residential split / packaged (ICC board) | Moderate | B |
| 83 | Indicates condenser coil temperature fault — abnormal sensor reading | Residential split / packaged (ICC board) | Moderate | B |
| 84 | Indicates outdoor ambient temperature fault — abnormal sensor reading | Residential split / packaged (ICC board) | Low | B |
| 93 | Indicates internal control fault — control board malfunction | Residential split / packaged (ICC board) | High | B |
| d1 | Indicates no shared data (communicating system) | Residential split / packaged (ICC board) | Moderate | B |
| d3 | Indicates airflow CFM mismatch — the air handler cannot meet the system airflow requirement | Residential split / packaged (ICC board) | Moderate | B |
| D4 | Indicates memory card data mismatch with the control board | Residential split / packaged (ICC board) | Low | B |
| d8 | Indicates old shared data — system data is obsolete | Residential split / packaged (ICC board) | Low | B |
Before you act on a code
- Do not treat 0, c, C or t as faults — they are normal operating states.
- L4 (locked rotor) and 5 (open circuit) point at the compressor or its start and run circuits: leave the system off and have it inspected.
- Rheem ductless mini-split-specific codes are still in technical review and are not published here.
Corroborated across independent technical sources
How to identify your system
- Note the exact character, including its case, and whether it is steady or flashing.
- Note whether an L prefix is present — that indicates a lockout rather than a first occurrence.
- Photograph the outdoor unit's data plate before contacting a technician.
No code showing? Start from the symptom
Rheem error codes — common questions
My Rheem board shows c — is something wrong?
No. Lower-case c means first-stage cooling is active, and a flashing c means an anti-short-cycle or minimum-run timer is counting. Upper-case C is second-stage cooling. These are normal operating states.
What does Rheem code 3 mean?
3 reports short cycling: each of the last four compressor cycles was under three minutes. That points at control, charge or load problems rather than a single failed part, and repeated short cycles shorten compressor life.
What does L21 mean on a Rheem?
21 is a low-pressure control open, and the L prefix with a flashing display indicates active low-pressure trip protection. Low pressure usually means lost refrigerant charge or restricted airflow, both of which need a technician to diagnose properly.
Rheem shows 27 — is that the AC or the power supply?
27 is a low or no line voltage fault, which describes the supply reaching the unit rather than a fault inside it. It is worth having the supply and isolator checked before parts are considered.
Need this looked at properly?
Call or send a photo on WhatsApp and we will tell you whether it needs an inspection, and what the work involves, before anyone travels.
Sources consulted
- Two independent Rheem ICC control-board technical references with matching entries