Coleman air conditioner shows E9 and may not start; often associated with low-voltage or power supply problems.

Safety: Turn OFF breakers before tightening any electrical connections. Use a non-contact tester to confirm power is off.

• Check breakers and disconnects: Verify the indoor and outdoor breakers are ON and the outdoor disconnect is fully inserted. Reset any tripped breakers once; if they trip again, stop and investigate further.
• Inspect control board fuse: Open the indoor unit’s control compartment. Look for a small automotive-style blade fuse (3–5A) on the Coleman control board. If blown, replace with the same rating. If it blows again immediately, there is a short in the low-voltage circuit.
• Test transformer output: With power ON and extreme caution, measure voltage at the transformer secondary (usually 24V). If there is no output, replace the 24V transformer with a Coleman-approved part.
• Inspect wiring: Look for shorted thermostat wires, especially where they pass through metal knockouts without grommets. Repair damaged insulation and secure with grommets or bushings.
• Clear the code: After correcting issues, cycle power to the system and thermostat to clear E9. Confirm normal operation.

Note: Repeated fuse blowing indicates a persistent short that should be located with a meter rather than trial-and-error.