Cool on the Highway, Warm in Traffic

Test each hypothesis against the numbers.

Charge. Static 800 kPa at 32 °C is about right for R-134a, and the recharge was verified by weight against spec. Overcharge would raise both sides at all speeds and would not improve to a near-normal vent temperature at 2,000 rpm. Undercharge would give a low high side everywhere. Charge is not the problem.

Compressor. A weak compressor or a lazy variable-displacement control valve gives the opposite pattern: a low high side and a high low side at idle that improve with rpm. Here the high side at idle is 1900 kPa - excessively high - which is the compressor working hard against something, not failing.

Condenser heat rejection. This is the fit. At idle, 1900 kPa corresponds to a condensing temperature far above ambient - an approach of roughly 25–30 °C where 10–15 °C is expected. At 2,000 rpm, ram airflow supplements the fan, the high side falls to 1500 kPa and vent temperature drops to 8 °C.

Conclusion: available airflow across the condenser is insufficient at idle, so head pressure climbs, the low side climbs with it, and capacity falls. The fan "turning" is not proof of adequate airflow - it is proof of rotation only.

Prove it before you touch the system:

1. Water-mist test. With the engine idling and AC on max, lightly mist the condenser with a garden sprayer. If the high side drops sharply and vent temperature falls, heat rejection is confirmed as the bottleneck. This is the single most decisive test you can run.
2. Measure air temperature rise across the condenser. Ambient in, ambient out - a healthy condenser adds roughly 10–20 °C to the air. A small rise means the air is bypassing or the tubes are restricted.
3. Check the fan properly: blade condition (cracked, flexing, or an aftermarket fan with the wrong pitch), shroud integrity and its seals to the condenser, and actual commanded current against spec - a fan that spins at 60% of design speed still 'turns'.
4. Check for air bypass: missing or torn foam seals between condenser and radiator, a missing lower air dam, or a fan shroud gap. At idle, the fan pulls whatever is easiest - if the shroud is broken, it recirculates hot air.
5. Look for obstructions in front of the condenser. Aftermarket transmission or oil coolers zip-tied ahead of the condenser are a common cause; so is a bug screen or a winter cover left in place.
6. Scan for fan duty cycle and any condenser-temperature-related derate.

Do not add refrigerant. The charge is verified and adding to a high-head-pressure system makes it worse and can slug the compressor.

That pattern - high low side, low high side at idle, improving with rpm - points at compressor displacement, not airflow. The compressor is not pumping enough at low speed, so suction pressure stays high and discharge pressure stays low. At 2,000 rpm the extra strokes mask the deficiency.

Changed approach:

1. Verify charge first anyway - an undercharge can mimic a weak compressor. Confirm by weight and by checking static pressure against ambient.
2. On a variable-displacement compressor with an electronic control valve, read the valve duty cycle or current on the scan tool and compare to the commanded value. If the PCM commands full stroke and the valve current is wrong or static, test the valve circuit before condemning the compressor.
3. Bypass test: command the valve to maximum and watch for a corresponding pressure change. If pressure does not follow the command, the valve or the compressor's internal swash plate is suspect.
4. Confirm mechanically with a pressure-rise test and by checking for a worn or slipping clutch, belt condition and pulley alignment.
5. Rule out a restriction on the suction side - a crushed line or a blocked evaporator will look similar and is far cheaper to fix.

Only after the control system and circuit are cleared do you quote a compressor. On these units the valve is often available separately, and diagnosing the valve versus the compressor is the difference between a small invoice and a large one.