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Discharge Air Temperature Below 40°C During Heating

Likely causes

Refrigerant shortage

Check: low high-side pressure → reduced condensing temperature

What to do: Record high/low pressure and discharge/suction temperature simultaneously → identify refrigerant shortage pattern (low HP, high superheat)

Indoor heat exchanger fouled

Check: reduced air-to-refrigerant heat transfer

What to do: Measure 4-way valve coil voltage (AC220V or DC12V) → if correct voltage but incomplete switching, replace valve

4-way valve incomplete switching

Check: refrigerant partially leaking to cooling circuit

What to do: Measure indoor coil airflow and clean filter → clean coil surface and recheck discharge temperature

Compressor compression efficiency degraded (worn valves)

Check: cannot raise discharge temperature

What to do: Check compressor current vs. frequency graph → if current is low and frequency is at upper limit, reconfigure inverter parameters

Inverter frequency upper limit restricted

Check: insufficient compressor capacity

What to do: If refrigerant shortage confirmed: detect leak and recharge; verify R-410A high pressure normal range of 22–25 bar

Field tip

To check 4-way valve: in heating mode, touch valve body — if temperature difference between cooling-side and heating-side pipes is less than 10°C, incomplete switching is confirmed

All 565 cases work offline in R-Pro, with error codes for 62 brands and P-T data for 108 refrigerants.

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