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.
Accuracy notes
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.
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
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,… E5
The evaporator freeze sensor is open or reading out of range. Because… Er
On the Coleman-Mach multi-zone LCD thermostat, 'Er' appears in the… Heat-pump strike condition
In electric-heat (heat-pump) mode the thermostat flashes the 'Elec'…
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)
● Checked against 2 manufacturer documents · 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