If it runs cold intermitently, there is enough refrigerant in the system for it to work.

Low reading from the high side (engine running) can indicate the compressor insnt compressing.

It's intermintent because the variable swash plate in the compressor is on the low compression setting when it should be high, thus no cooling. Sometimes it goes to the correct setting and you will get cold air.

Another check is when you lose AC cooling, go up front and check if the compressor clutch is engaged. If it is, it's probably the compressor.

What you will see is cooling is gone, compressor clutch engaged, pusher fan will be off.

Another thing, these variable displacement systems dont engage the clutch on/off to regulate temp like older systems, it adjusts the compression internally, so when the AC is on, the clutch does not disengage unless you turn AC off.

These dont have a relay, they are directly connected to the climate control computer.

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04 X5 3.0i auto
03 X5 4.6is