Is there an automatic shut-off in the AC that shuts down the coolant completely when at an idle?

Chances are. your AC is not cycling anymore. The most common reason that this happens is due to a small leak in the system that allows the refrigerant to escape and when enough has leaked out, the low pressure switch is activated to shut the compressor down to make sure thatthe compressordoes not burn itself out.When this happens, you willnotice the compressor running for a short time and then shutting off. The system needs to be recharged and then leak tested, repaired, and recharged. Generally, a fitting or a hose has leaked and once it is repaired you AC will work fine again.