The compressor not running is a fairly common thing when the freon pressure is real low (like almost empty). On most cars, it's a safety feature to keep the compressor from burning itself out. It can be tested by jumping out the low pressure switch for a second). If the compressor comes on, then you know it's low. (unfortunately, I don't know where your low pressure switch is located).

__________________
2008 ML350
2007 Honda Element
2007 Honda Accord
2009 Honda Civic