Variable Refrigerant Flow VRF Warning (System Continues in Backup Mode)

LG Multi V CH74 Error: High Pressure Sensor Fault — Transducer or Wiring

Published: 2026-06-14

⚠️ Warning Diagnostic

The LG Multi V CH74 error indicates the outdoor unit main PCB has detected an abnormal signal from the high pressure transducer — either an open circuit (sensor disconnected or failed), a short circuit (wiring damage or sensor internal short), or an out-of-range reading that the controller interprets as a sensor fault rather than an actual pressure condition.

CH74 vs CH75 — Know the Difference

CH74 is a sensor FAULT. CH75 is a sensor VALUE (actual high pressure condition). Do not treat CH74 as a high-pressure trip — the system is not over-pressurized, the sensor that measures pressure is not working correctly. Adding refrigerant or adjusting the condenser fan in response to CH74 will waste time and may create a real problem where there wasn't one.

🔍 Symptoms Checklist

⚠️ CH74 displayed on wired remote controller
⚠️ HVAC system still running but in backup/protection mode
⚠️ Cooling or heating capacity noticeably reduced

🛠️ OEM Replacement Parts

Part Name	OEM Part Number	Est. Price
High Pressure Sensor (Transducer)	`EBG61322701`	$310
Pressure Sensor Wiring Harness	`EBG61294001`	$85

📋 Interactive Diagnostic Procedure

Click each step to expand detailed diagnostic instructions. Follow in sequence — each step builds on the previous one.

1 Check Pressure Sensor Connector

The high pressure sensor is mounted on the outdoor unit's discharge line. Inspect the 3-pin connector for corrosion, moisture, or loose fit. The sensor connector is located in the outdoor unit electrical compartment — it's exposed to condenser airflow and is prone to moisture-related corrosion. Clean with electrical contact cleaner, reconnect firmly, and clear the error from the controller.

2 Test Sensor Output Voltage

The LG high pressure sensor outputs 0.5-4.5V DC proportional to pressure (typically 0-725 psi range). With the system off (equalized pressure), the sensor should output approximately 1.0-1.5V DC corresponding to static system pressure. If output is 0V or 5V (open circuit or short), the sensor has failed. Measure at the sensor connector (between signal and ground pins) with the connector connected — back-probe the connector.

3 Replace and Calibrate

If the sensor output voltage is incorrect, replace the sensor. After replacement, the LG Multi V system automatically calibrates — no manual calibration is needed. However, you must clear the CH74 error from the controller's service menu (hold the 'Mode' and 'Fan Speed' buttons simultaneously for 5 seconds to enter the service menu). Test system operation in both cooling and heating modes after replacement.

Frequently Asked Questions

CH74 vs CH75 — how do I tell which one I have?

CH74 = sensor fault (the pressure reading is unreliable). CH75 = actual high pressure condition (the sensor is working and reporting a real high pressure). If the error occurred immediately after a power cycle or during mild weather when high head pressure is unlikely, it's probably CH74. If it occurred on a 100°F day with a dirty condenser coil, it's probably CH75. LGMV diagnostic software will show the actual sensor reading — check it before proceeding.

Can I temporarily bypass the high pressure sensor to keep the system running?

No. Disconnecting or bypassing the high pressure sensor will trigger a CH74 fault (open circuit detected) and the system will default to backup/protection mode with reduced capacity. More importantly, running without a functioning high pressure sensor removes the primary compressor protection mechanism — you could destroy a $4,000 inverter compressor with no warning.

🔗 Related Error Codes — Variable Refrigerant Flow VRF

Other diagnostic guides in the same equipment category. Common failure patterns often share root causes — cross-referencing speeds up diagnosis.

Variable Refrigerant Flow VRF Critical Interlock

⚡ Fault-Induced Energy Waste Estimator

When HVAC equipment runs with active error codes, it operates inefficiently and wastes electricity. Estimate the monthly cost of delaying repairs. All calculations run locally in your browser.

Unit Power Consumption (kW)

Extra Run Time Due to Fault (Hours/Day)

Local Electricity Rate ($/kWh)

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References & Industry Standards

ASHRAE 15 — Safety Standard for Refrigeration Systems
ASHRAE 34 — Refrigerant Designation & Safety Classification
AHRI 550/590 — Water-Chilling & Heat Pump Packages
SMACNA — HVAC Duct Construction Standards
Manufacturer Service Manuals — Carrier, Trane, York, Daikin, Lennox

LG Multi V CH74 Error: High Pressure Sensor Fault — Transducer or Wiring

🔍 Symptoms Checklist

🛠️ OEM Replacement Parts

📋 Interactive Diagnostic Procedure

Frequently Asked Questions

🔗 Related Error Codes — Variable Refrigerant Flow VRF

Daikin VRV U4 Error: Indoor-Outdoor Communication Failure

Mitsubishi City Multi Error 7100: High Pressure Protection — Outdoor Unit

LG Multi V Error CH24: High Pressure Sensor Malfunction

Toshiba SMMS U1 Error: Indoor Unit Address Duplication

Daikin VRV U2 Error: Power Supply Voltage Abnormal — Phase Loss Detection

Mitsubishi City Multi Error 7102: High Discharge Temperature Protection

LG Multi V Error CH34: Inverter Compressor Overload — Drive Fault

Toshiba SMMS U4 Error: Outdoor Unit PCB Communication Failure

⚡ Fault-Induced Energy Waste Estimator

References & Industry Standards