Coleman-Mach Air Conditioner: “HI”
info RV air conditioner error codes
What it means
The thermostat senses a temperature above the top of its measurable range. On the digital wall thermostat this shows when the sensed temperature is above about 99 F (37 C). Like LO, it is a display range limit rather than an equipment fault.
Most likely causes
- Actual ambient temperature at the sensor is above 99 F / 37 C (very hot coach, sun-baked sensor) most likely
- Sensor mounted in direct sun, near a heat source, or high near the ceiling where heat collects common
- Failing or shorted temperature sensor reading artificially high less common
Safe checks you can do yourself
- Confirm the cabin really is extremely hot; if so HI is expected behavior, not a fault.
- Start cooling and watch whether the display returns to a number once the room drops below 99 F.
- Check the sensor location is not in direct sunlight, against a hot exterior wall, or right at the ceiling.
- Verify the F/C unit setting.
How to reset / clear HI
- Let the cabin cool below 99 F (37 C); the HI indication clears automatically.
- If HI persists in a normal-temperature room, manual reboot: hold the knob ~12 seconds until it counts down and powers off, then release to reboot.
When to call a technician
HI keeps showing in a room that is clearly not that hot, indicating a faulty sensor or thermostat that should be replaced.
Applies to
9420*381 · 9420*382 · 8330-series Digital Wall Thermostat · TSR2 (8330-3862)
FAQ
What does Coleman-Mach Air Conditioner code "HI" mean?
The thermostat senses a temperature above the top of its measurable range. On the digital wall thermostat this shows when the sensed temperature is above about 99 F (37 C). Like LO, it is a display range limit rather than an equipment fault.
How do I reset Coleman-Mach Air Conditioner HI?
Let the cabin cool below 99 F (37 C); the HI indication clears automatically. If HI persists in a normal-temperature room, manual reboot: hold the knob ~12 seconds until it counts down and powers off, then release to reboot.
What is the most common cause of HI on a Coleman-Mach Air Conditioner?
The most likely cause is actual ambient temperature at the sensor is above 99 f / 37 c (very hot coach, sun-baked sensor).
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Sources
- Installation, Operation & Application Guide for Digital Wall Thermostat 9420*381 & 9420*382 — Doc 1980R189, Set Temperature Range section (Airxcel, Inc. / Coleman-Mach (RV Products Division))
Note: HI is an out-of-range display, not a numeric error code. The 99 F / 37 C threshold is from the official 9420/8330 manual; other thermostat generations may vary.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.