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.
Accuracy notes
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.
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 link with the… E2
The indoor (room) temperature sensor reads as an open circuit or its… E3
The indoor (room) temperature sensor is reading as shorted. As with E2,… E4
The outdoor temperature sensor (fitted on heat-pump-equipped models) is… E5
The evaporator freeze sensor is open or reading out of range. Because… Heat-pump strike condition
In electric-heat (heat-pump) mode the thermostat flashes the 'Elec'…
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))
● Checked against 1 manufacturer document · Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual. How we verify