What CH34 means
The mechanical high-pressure switch is a safety device that physically cuts the compressor circuit when the discharge pressure exceeds a preset limit (typically around 4.15 MPa for R410A systems). CH34 appears when this switch opens.
LG AC CH34 Error — High Pressure Switch Fault & Fix
CH34
Quick answer
CH34 means the high-pressure switch on the outdoor unit has tripped — refrigerant pressure on the discharge side is dangerously high.
What does the CH34 code mean?
CH34 is a high-pressure switch trip. The refrigerant discharge pressure has exceeded the safety limit and the mechanical switch has opened.
Common causes
- Dirty condenser coil (most common — heat cannot be rejected)
- Outdoor fan failure or blockage
- Refrigerant overcharge (too much gas added during servicing)
- Non-condensable gases in the system (air or nitrogen left after poor vacuum)
- Ambient temperature extremely high with no airflow
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How to fix the CH34 error
Power off for 30 minutes
Pressure needs time to drop before the switch resets.
Clean the condenser coil
This is the number one cause — a thorough hosing resolves most CH34 cases.
Check the outdoor fan
Make sure it runs and has clearance.
Remove obstructions
Ensure nothing is blocking airflow around the outdoor unit.
Restart
If CH34 clears, the cause was poor heat rejection.
Persistent CH34
Call a technician to check refrigerant charge and for non-condensables.
Safety first: High refrigerant pressure is dangerous. Never attempt to relieve pressure yourself. Let the system cool and call a professional.
Part you may need: Outdoor condenser cleaning / refrigerant service
If the system was recently serviced and CH34 appears, the tech may have overcharged the gas.
Frequently asked questions
Will CH34 reset on its own?
The mechanical pressure switch resets automatically once pressure drops below the reset point. But the underlying cause must be fixed or it will trip again.
Can high ambient temperature cause CH34?
Only if combined with poor airflow (dirty coil, blocked fan). A properly maintained unit handles high ambient temperatures.
