Indoor unit will not respond to remote, display shows E0 and unit does not start cooling or heating.

Safety first: Turn off the Tristar air conditioner at the wall switch or breaker and unplug it if it is a portable or window unit. Wait at least 5 minutes before touching any internal components.

Steps to try:

• Power reset: Turn the breaker off for 5–10 minutes, then restore power. This can clear minor EEPROM glitches.
• Check power supply: Verify the outlet or dedicated circuit is delivering correct voltage with a multimeter. Low or unstable voltage can trigger E0.
• Inspect indoor PCB connections: Remove the front cover, locate the indoor control board, and check that all multi-pin connectors are fully seated and free of corrosion or burn marks.
• Look for surge damage: Examine the PCB for bulged capacitors, burnt tracks, or a burnt smell. If present, the board must be replaced.
• Factory reset (if available): Some Tristar models allow a reset via a small button on the PCB or a specific remote key combination (consult the service manual). Perform the reset and test operation.

When to call a technician: If E0 returns immediately after a reset and wiring is intact, the indoor main PCB/EEPROM is likely defective and should be replaced by a qualified technician.