- Park the car overnight.

- In the morning, start slow and drive slowly...if AC works fine for a few miles (bc coolant temp is not hot yet), then starting getting warm as you drive, then trouble-shoot the heater valve.

- Another approach is GENTLY clamp the heater hoses x2, leave car on driveway, run AC to see if it gets cold. This is another way to diagnose heater valve issues.

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT