Coleman-Mach Air Conditioner: “E4”
warning RV air conditioner error codes
What it means
The outdoor temperature sensor (fitted on heat-pump-equipped models) is open or reading out of range. The thermostat locks out heat-pump operation, but air conditioning, fan, and furnace functions can still run.
Most likely causes
- Open or disconnected outdoor temperature sensor (heat-pump models) most likely
- Damaged or corroded outdoor-sensor wiring/connector common
- Failed outdoor temperature sensor common
- Thermostat configured for heat-pump sensor that isn't present/working less common
Safe checks you can do yourself
- Confirm whether your unit is a heat-pump model that actually has an outdoor sensor.
- Check the outdoor-sensor connector and wiring for looseness, corrosion, or damage.
- Power-cycle the system to clear a transient reading.
- Use A/C, fan, or furnace in the meantime if needed (these stay available).
How to reset / clear E4
- Turn OFF the A/C breaker, wait ~60 seconds, then restore power.
- If E4 clears, the fault was transient.
- If it returns, the outdoor sensor or wiring likely needs service.
When to call a technician
E4 persists after checking the outdoor-sensor wiring and a power cycle, or the sensor must be replaced and you want heat-pump function restored.
Applies to
Coleman-Mach single-zone LCD wall thermostat (heat-pump-equipped / select models) · Coleman-Mach heat-pump rooftop A/C systems
FAQ
What does Coleman-Mach Air Conditioner code "E4" mean?
The outdoor temperature sensor (fitted on heat-pump-equipped models) is open or reading out of range. The thermostat locks out heat-pump operation, but air conditioning, fan, and furnace functions can still run.
How do I reset Coleman-Mach Air Conditioner E4?
Turn OFF the A/C breaker, wait ~60 seconds, then restore power. If E4 clears, the fault was transient. If it returns, the outdoor sensor or wiring likely needs service.
What is the most common cause of E4 on a Coleman-Mach Air Conditioner?
The most likely cause is open or disconnected outdoor temperature sensor (heat-pump models).
Related · Coleman-Mach air conditioner
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Sources
- Coleman air conditioner error codes (E4 outdoor temperature sensor open/out of range, heat-pump lockout) — Coleman-Mach Single Zone LCD thermostat code list (E4) (Twintech Heating and Cooling)
- E1 fault on thermostat (thread including E4/E5 code reference) — Coleman-Mach thermostat E4 outdoor sensor fault (Heartland Owners Forum)
Note: Original-English compilation mirroring the Coleman-Mach single-zone LCD code list; manufacturer PDF table not directly openable. E4 applies only to heat-pump-equipped (select) models with an outdoor sensor; LCD-display thermostats only.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.