Cosmo / Cosmo Series

Cosmo H3 error code

H3 means the compressor protection circuit has stopped operation because the system is overloaded or overheating. Restricted airflow is the main safe homeowner item to rule out.

All Codes

Urgency: advisory
Verified: Jul 31, 2026
Fix path: Technician

What it means

H3 means the compressor protection circuit has stopped operation because the system is overloaded or overheating. Restricted airflow is the main safe homeowner item to rule out.

Urgency

advisory

Clear obvious airflow restrictions once. If H3 returns, schedule service because compressor protection is involved.

Likely causes

Restricted indoor or outdoor airflow
Dirty filter or heat exchanger
System overheating during heavy operation
Compressor overload condition

Homeowner fix

Turn the system off for at least 10 minutes, clean the filter, and clear debris from the outdoor coil area. Do not open the cabinet or bypass any protection.

When to call a pro

Call a licensed HVAC technician if H3 returns, the outdoor unit is very hot, or cooling/heating is weak after airflow is clear.

This code points to refrigerant or sealed-system, compressor, and electrical or inverter work - get repair quotes from contractors in your area.

Get repair quotes

Repair vs replace

Many overload trips trace to airflow or serviceable refrigerant conditions. Compressor or inverter repairs on older systems should be weighed against replacement.

See Cosmo mini-splits

Your Cosmo model

Cosmo Series model pages in the Cosmo catalog help compare this repair path with current replacement options.

See Cosmomini-splits ->

For your technician

Technician note: verify indoor/outdoor airflow, coil cleanliness, operating pressures, refrigerant charge, compressor current, and overload circuit before clearing H3. Page context: Cosmo maps this display to the Cosmo Series line; source: TOSOT Direct Cosmo Series product-document manual links plus TOSOT Direct mini-split error-code guide and FAQ; display convention: match the letter H and three marker exactly before comparing neighboring codes.

Which systems show it

Cosmo Series

Sold under more than one brand

Shared with TOSOT. Cosmo and TOSOT document this code from the same manufacturer source, so H3 means the same thing on either badge and the steps above apply.

Open TOSOT H3

Related troubleshooting

Use the symptom guide alongside the exact display code if the unit is flashing, cycling, or showing comfort symptoms.

Mini split indoor unit freezing up Mini split weak airflow Mini split not heating

Source

TOSOT Direct Cosmo Series product-document manual links plus TOSOT Direct mini-split error-code guide and FAQ

Document: TOSOT Direct Cosmo Series product-document manual links plus TOSOT Direct mini-split error-code guide and FAQ

Sourced Jul 2026

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