I have a Mercedes 240d and the a/c is no longer working properly. The compressor engages as it should but it is not producing cold air. I checked the pressures with the engine at idle and found low side about 90psi and high side about 94psi. Is the compressor shot, or is it something else like the expansion valve? The a/c was working well for 15 months before this. It has R12 refrigerant. I did searches on this site and on the web but could not find out what my guage readings mean. Any help appreciated.

I don't think it could be the expansion valve with such a small pressure difference. Probably the valves in the compressor.