Coleman-Mach Air Conditioner: “Er”
warning RV air conditioner error codes
What it means
On the Coleman-Mach multi-zone LCD thermostat, 'Er' appears in the temperature area of the display when the measured ambient temperature is outside the thermostat's usable range, or when there is a problem with one of the remote temperature sensors. It signals the thermostat cannot show or act on a valid temperature for that situation/zone.
Most likely causes
- Remote (zone) temperature sensor disrupted, disconnected, or faulty most likely
- Loose or corroded sensor wiring at the zone control box common
- Actual room temperature outside the thermostat's display/operating limits less common
- Failed sensor or board input less common
Safe checks you can do yourself
- Identify which zone shows 'Er' and check that zone's remote sensor connector and wiring.
- Confirm each zone board has proper 12V DC and the green LED behavior is normal.
- Power-cycle the system to clear a transient reading.
- Rule out genuine temperature extremes (e.g. very cold/hot coach interior).
How to reset / clear Er
- Turn OFF the A/C breaker, wait ~60 seconds, then restore power.
- Let the thermostat re-detect connected zones on startup.
- If 'Er' returns for a specific zone, inspect/replace that zone's remote sensor (qualified service).
When to call a technician
'Er' stays for a zone after checking that zone's sensor wiring and a power cycle, or a remote sensor/board must be replaced.
Applies to
Coleman-Mach multi-zone LCD wall thermostat (e.g. 9330-33 / 9430 multi-zone control packages) · Coleman-Mach zone-controlled rooftop A/C systems with remote room sensors
FAQ
What does Coleman-Mach Air Conditioner code "Er" mean?
On the Coleman-Mach multi-zone LCD thermostat, 'Er' appears in the temperature area of the display when the measured ambient temperature is outside the thermostat's usable range, or when there is a problem with one of the remote temperature sensors. It signals the thermostat cannot show or act on a valid temperature for that situation/zone.
How do I reset Coleman-Mach Air Conditioner Er?
Turn OFF the A/C breaker, wait ~60 seconds, then restore power. Let the thermostat re-detect connected zones on startup. If 'Er' returns for a specific zone, inspect/replace that zone's remote sensor (qualified service).
What is the most common cause of Er on a Coleman-Mach Air Conditioner?
The most likely cause is remote (zone) temperature sensor disrupted, disconnected, or faulty.
Related · Coleman-Mach air conditioner
The single-zone LCD thermostat has lost its communication li… E2
The indoor (room) temperature sensor reads as an open circui… E3
The indoor (room) temperature sensor is reading as shorted. … E4
The outdoor temperature sensor (fitted on heat-pump-equipped… E5
The evaporator freeze sensor is open or reading out of range… Heat-pump strike condition
In electric-heat (heat-pump) mode the thermostat flashes the…
Sources
- RVP (Airxcel) - Thermostat Model Multi Zone For 9330-33 Operation Guide — Multi-zone thermostat operation guide — 'Er' displayed for out-of-range ambient temperature or remote-sensor problem; 'system does not operate below 9.75 VDC' (Forest River, Inc. (OEM-hosted Airxcel/RVP manual))
Note: Confirmed from the OEM-hosted Airxcel/RVP multi-zone operation guide PDF (text extracted directly). The multi-zone LCD thermostat uses 'Er' rather than the E1-E5 numbering used by the single-zone LCD thermostat; wording is an original-English summary, not copied manual prose.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.