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Coleman-Mach Everest VS-18 error code E9

FaultAir Conditioning (Rooftop)Verified against the manufacturer's manual

Communication Fault Between the ACTH3 Thermostat and the Main Control Board - interface circuit is damaged, OR wiring sequence is wrong, OR communication line has poor contact

What to check, and in what order, is in the app. The flow VS-18 E9 - Communication Fault Between ACTH3 Thermostat and Rooftop PCBA walks this code step by step with the pass/fail measurements, wiring schematics and procedures that go with it, and it works offline in the bay.

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Models covered

{'id': 'coleman_standard', 'label': 'Standard Coleman-Mach (Mach series + Zone Control)', 'tagline': 'Mach 1 / 3 / 3+ / 8 / 10NDQ / 15 / Q plus 8-Series and 9-Series Zone Control. Standard 12 VDC 9-pin and zone-control architectures - the bulk of the Coleman-Mach rooftop lineup. (Excludes the Everest VS-18 inverter unit.)', 'flow_prefixes': ['ac_coleman_'], 'code_manufacturers': ['Coleman-Mach', 'Coleman Mach', 'RVP', 'Airxcel RVP', 'Coleman-Mach 8-Series Zone', 'Coleman-Mach 9-Series Zone', 'Coleman Mach (Mechanical)'], 'component_exclude_keywords': ['vs18', 'vs-18', 'everest']}, {'id': 'coleman_everest_vs18', 'label': 'Everest VS-18 (variable-speed inverter)', 'tagline': 'Variable-speed inverter rooftop A/C with the E1-E9 / dE digital fault-code display and ACTH3 wall thermostat. Distinct inverter control board - its codes, sensors, and parts do NOT apply to the standard Mach lineup.', 'flow_prefixes': ['vs18_'], 'code_manufacturers': ['Coleman-Mach Everest VS-18'], 'component_keywords': ['vs18', 'vs-18', 'everest'], 'symptom_keywords': []}

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