Daikin E4 Error Code — What It Means
The E4 error code on Daikin systems indicates actuation of the low pressure switch (LPS). This means the system detected abnormally low refrigerant pressure and shut down the compressor to prevent damage. The low pressure switch is a protective device that monitors suction pressure. When pressure drops too far below normal operating range, the switch opens and the unit stops.
This fault points to a refrigerant-side problem rather than an electrical or sensor glitch in most cases. The system is telling you that something is preventing adequate refrigerant pressure from building in the low side of the circuit. It could be low charge, a blockage, or occasionally a faulty sensor itself.
Common Causes
- Refrigerant leak or low charge The most common trigger is loss of refrigerant through leaking flare joints, brazed connections, or coil pin-holes, resulting in insufficient system pressure.
- Blocked or stuck expansion valve A restricted expansion valve prevents refrigerant flow and causes pressure drop on the low side.
- Clogged filter drier If your system has a filter drier in the liquid line, contamination or moisture can choke flow and starve the evaporator.
- Faulty low pressure switch or sensor The switch itself may fail or the wiring connector may have poor contact, causing false trips even when pressure is normal.
- Outdoor PCB fault The control board can misread or mishandle the pressure signal, though this is less common than actual refrigerant issues.
Step-by-Step Fix {#fix}
- Confirm the error code by checking the display or using the controller’s diagnostic mode per your model’s manual to verify E4 is currently active or logged.
- Connect a manifold gauge set to the service ports and measure actual suction and discharge pressures with the unit off, then compare to expected values for your refrigerant type and ambient conditions.
- Inspect all refrigerant joints and coils for leaks using electronic leak detector or soap bubbles, paying close attention to flare fittings and anywhere you see oil staining.
- Check the expansion valve and filter drier for restriction by feeling temperature drop across each component and looking for frost or abnormal temperature difference that suggests blockage.
- Test the low pressure switch and wiring by measuring continuity across the switch terminals and inspecting connectors for corrosion or loose contact if pressures measure normal.
- Repair any confirmed leak, then evacuate the system to remove air and moisture, and recharge to the nameplate specification by weight using a scale.
- Replace restricted components such as the expansion valve or filter drier if diagnostics confirm internal blockage, then evacuate and recharge before restarting.
Parts Often Needed
| Part | Notes |
|---|---|
| Low Pressure Switch (LPS) | Amazon | Match your outdoor unit model number. Needed if switch tests open or trips at normal pressure. |
| Expansion Valve | Amazon | Electronic or thermal type depending on system. Replace if blocked or malfunctioning. |
| Filter Drier | Amazon | Required after any repair that opens the refrigerant circuit. Match your line size and refrigerant. |
| Outdoor PCB / Control Board | Amazon | Verify by testing sensor inputs and switch continuity before replacing. Must match your exact model. |
When to Call a Pro
Call a licensed HVAC technician if you are not certified to handle refrigerants or lack a manifold gauge set and vacuum pump. Refrigerant work requires EPA certification and specialized tools. Also call if you find a leak but cannot access the joint for repair, if the system needs brazing, or if the fault returns after you have recharged and verified pressures. Outdoor PCB diagnosis and expansion valve replacement on VRV or complex systems often need factory training and software tools.