AirCon - not cold, but compressor working?

[more_fasterer]

Hi team,

I'm hoping someone can help me pinpoint what's going on with the climate control on my 2005 3.0d. This isn't the usual low refrigerant level or failed aux fan issue, at least I don't think it is anyway. The symptoms are:
- Air from the vents is always at ambient temperature
- Interior fan operates correctly
- No faults logged by any ECU
- A/C compressor runs when A/C button is turned on
- Aux fan runs when tested in INPA, but I didn't observe it running while letting the car idle with the climate control set to "max" for ~5 minutes
- The hard line from the compressor to the condenser gets hot, nearly too hot to touch
- Both the hard lines running alongside the engine from the firewall (i.e. to and from the evaporator) are neither hot nor cold to the touch

The car has done 190,000km (120,000mi). I expect a trip to the local aircon specialist is in order, but I'd like to know if there's something I should be looking at outside of the refrigerant system. It's potentially likely that they'll find the system pressures are OK, otherwise the compressor wouldn't kick in.

Any guidance appreciated!