AC Cold on the Motorway, Warm in Traffic
Vehicle
- ModelTraining Hatch 1.6
- Engine1.6 16V
- Mileage88,000 km
Customer complaint
The air conditioning blows cold when driving but warm when the car is stationary in traffic. The compressor clutch engages normally.
History
The system was recharged six months ago without a leak test. No warning lights.
Live data
- Ambient temperature32 °C
- High side pressure in trafficVery high
- Low side pressureNormal to slightly high
Measurements
- Condenser fan, engine hotNot running
- Condenser fan, powered directlyRuns at both speeds
- Vent temperature, motorwayCold
- Vent temperature, stationaryWarm
Diagnostic case
Next step — Reasoning.
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Confirmed cause
The condenser cooling fan is not being commanded, so the high side pressure rises in traffic and cooling collapses. The fan motor itself is serviceable.
Reasoning
The pattern — cold at speed, warm when stationary — is the signature of insufficient condenser airflow, because ram air does the job on the motorway. Powering the fan directly proves the motor works, which localises the fault to the control circuit (relay, fuses, wiring or module command). The very high high-side pressure confirms heat is not being released.
Recommended repair
- Diagnose and repair the condenser fan control circuit (relay, fuses, wiring or module).
- Re-test high-side pressure and vent temperature in traffic conditions.
- Check the refrigerant charge afterwards and leak-test, since the earlier recharge was done without one.