Daikin E4

What does Daikin E4 mean?

The E4 code means the low-pressure switch has opened or the low-pressure sensor has reported pressure below the cutout. Low suction pressure means the compressor is pulling against a starved coil, which risks slugging and oil-return failure if allowed to continue. The PCB trips the compressor to protect it. Refrigerant loss, a stuck expansion valve, and blocked strainers or service valves are the usual suspects on E4.

Symptoms

• Compressor stops shortly after startup and E4 appears
• Suction line at the outdoor service valve is warm instead of cold
• Indoor coil shows uneven frosting or no temperature change
• Bubbling visible in the sight glass if fitted
• Gauge set reads suction pressure below the cutout threshold

Common causes

• Refrigerant undercharge from a leak
• Stuck or failed electronic expansion valve
• Clogged liquid-line filter-drier or strainer
• Closed or partially closed service valve
• Defective low-pressure switch, sensor, or connector contact

Diagnostic steps

1. 01

   Confirm service valves are fully open

   Backseat both the liquid and gas service valves. A partially shut valve mimics undercharge and trips LPS quickly.

2. 02

   Gauge the system

   Connect a manifold and read suction and liquid pressures. Compare against the charging chart for the current indoor and outdoor conditions.

3. 03

   Leak-check the system

   Bubble-test the service ports, braze joints, and flare fittings with soap solution or an electronic leak detector. Document any findings.

4. 04

   Inspect the filter-drier

   Feel across the drier for a temperature drop, which indicates restriction. Replace the drier and evacuate before recharging.

5. 05

   Test the LPS circuit

   With the system at rest and pressures equalized, continuity-check the LPS. Replace the switch or sensor if open or drifted.

6. 06

   Verify EEV operation

   On inverter units, observe the EEV step position in diagnostic mode and confirm it opens from the closed position. A stuck valve needs coil or body replacement.

When to call a professional

Call a licensed technician any time E4 is driven by refrigerant-side faults. Leak detection, repair, evacuation to spec, and weighed recharge all require EPA 608 or local certification and calibrated tools. Expansion-valve work, filter-drier replacement, and brazing on a charged system are not DIY territory. If the pressure sensor itself is suspect, swap must be done with proper recovery to avoid venting refrigerant to atmosphere. Get a pro out before pressures drop further and the compressor loses oil return.