Poor Idle Cooling Plus a Side-to-Side Temperature Split

The idle pressure set is the abnormal one.

• At 1,800 rpm the system looks healthy: low side 2.3 bar, high side 15.8 bar, 9 C vent. That is close to a normal R-1234yf performance curve at 35 C ambient.
• At idle the low side is high at 3.9 bar while the high side is low at 11.5 bar, and vent temperature rises to 20 C. Both pressures converge toward each other.

What that pattern means:

• Low charge would drop the high side and the low side together, at all speeds - not just at idle. Ruled out by the 1,800 rpm data.
• Insufficient condenser airflow would push the high side up at idle. The high side is going down, and the fan and fins are verified. Ruled out.
• The remaining explanation is that compressor displacement is falling off at low rpm - a sticking or mis-calibrated variable-displacement control valve, or a drive belt that slips only under the higher torque at low engine speed. The compressor is not pumping enough at idle and catches up once rpm rises.

The side-to-side split is a separate fault. Both zone doors are commanded full cold, yet driver and passenger differ. Airflow and temperature control live downstream of the evaporator; a charge or compressor problem cools both outlets, just less. Two faults, and treating one will not resolve the other: verify the driver's blend door actually travels to its stop (command a sweep and watch actuator counts or feel the door), check the driver's side air-temperature sensor reading against an actual thermometer, and confirm the heater core door is fully closed on that side.

Recover and weigh the charge first.

Reasoning:

• The pressures are abnormal but not diagnostic by themselves for a control-valve fault. Recovering and weighing gives a hard number against 520 plus or minus 25 g and either eliminates charge as a variable or confirms it. Every subsequent decision depends on knowing the system is correctly charged and correctly oiled.
• It is also fast and non-destructive. If the charge is wrong, you may be finished; if it is right, you have a clean baseline for judging the compressor and the blend door.
• Diagnosing the blend door first would be reasonable if the pressures had been normal - but here the refrigeration data is not normal, so the charge must be settled before any pressure-based judgement is trusted.

Sequence:

1. Recover, weigh, and record; recharge by weight with the specified oil amount.
2. Re-run the idle and 1,800 rpm pressure sets.
3. If idle pressures still converge, test the compressor control valve per the manufacturer's procedure (valve current sweep against pressure response), and rule out belt slip under load.
4. Only then chase the driver's side temperature split, using the door sweep and a thermometer at each outlet.

Interpretation: 480 g is 40 g below nominal and 15 g below the bottom of the tolerance band (495 g).

That is a small undercharge - not enough by itself to explain a low side of 3.9 bar at idle, but enough that it must be accounted for.

What to do:

• Recharge to 520 g by weight and re-measure before concluding anything about the compressor. A partial charge can distort the low-side reading, and you will not be able to defend a compressor diagnosis on a system that was not full.
• Investigate where 40 g went. Small losses over seven years are normal seepage; a 40 g loss in one season is a leak. Leak-check the accessible joints, service ports, and the evaporator drain area, and record the result.
• If the idle pressures are still converging after a correct charge and the control valve sweep is out of range, replace the valve or compressor per the manufacturer's direction, then re-verify at idle and at 1,800 rpm.
• Keep the two complaints separate in the write-up. If the side-to-side split remains after the refrigeration repair, the blend door is a second, separately authorized repair - do not let the charge problem be used to explain away a door that never reached its stop.