Coleman-Mach Air Conditioner: “E3”
warning RV air conditioner error codes
What it means
The indoor (room) temperature sensor is reading as shorted. As with E2, the thermostat can't trust the room temperature, so heating and cooling are locked out while the fan can still run.
Most likely causes
- Shorted indoor/room temperature sensor most likely
- Sensor wiring shorted (pinched/chafed conductors touching) common
- Moisture or corrosion bridging the sensor terminals less common
- Failed thermostat input circuit less common
Safe checks you can do yourself
- Inspect the room-sensor wiring for pinched or chafed spots that could short the two conductors.
- Check the sensor connector for moisture, debris, or corrosion.
- Power-cycle the system to confirm the fault is persistent.
- Verify the sensor is the correct type for your thermostat.
How to reset / clear E3
- Turn OFF the A/C breaker, wait ~60 seconds, then restore power.
- If E3 clears and stays clear, it was transient.
- If it returns, the indoor sensor or wiring likely needs replacement.
When to call a technician
E3 persists after checking wiring and a power cycle, or the room sensor must be replaced.
Applies to
Coleman-Mach single-zone LCD wall thermostat · Coleman-Mach rooftop A/C systems using a remote/indoor room temperature sensor
FAQ
What does Coleman-Mach Air Conditioner code "E3" mean?
The indoor (room) temperature sensor is reading as shorted. As with E2, the thermostat can't trust the room temperature, so heating and cooling are locked out while the fan can still run.
How do I reset Coleman-Mach Air Conditioner E3?
Turn OFF the A/C breaker, wait ~60 seconds, then restore power. If E3 clears and stays clear, it was transient. If it returns, the indoor sensor or wiring likely needs replacement.
What is the most common cause of E3 on a Coleman-Mach Air Conditioner?
The most likely cause is shorted indoor/room temperature sensor.
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Sources
- Coleman air conditioner error codes (E3 shorted indoor temperature sensor) — Coleman-Mach Single Zone LCD thermostat code list (E3) (Twintech Heating and Cooling)
- Coleman air conditioner codes — Coleman-Mach thermostat E3 shorted indoor sensor (KDM Gas)
Note: Original-English compilation from RV HVAC references mirroring the Coleman-Mach single-zone LCD code list; manufacturer PDF table not directly openable. Some generic (non-RV) Coleman mini-split charts assign E3 to a fan-speed fault, so this record is scoped specifically to the Coleman-Mach RV single-zone LCD thermostat. LCD-display models only.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.