From another thread, this to me makes some kind of sense;
06-26-2012, 10:29 PM #23
Drives: 2010 Duramax; 2012 CTS-V Coupe
Join Date: Apr 2012
Location: Houston, Tx
iTrader Rating: 0 reviews
Keep in mind that your condenser is sandwiched between the heat exchanger and radiator. So if you were at normal operating temp and turned the car off on a hot day you now have a hot radiator and hot heat exchanger pouring heat into the cooler condenser. Heat equals pressure so when you turn the car off the condenser starts heating up quickly and building pressure in the A/C lines. The pressure switch in the A/C system see's the high pressure so it wont turn the compressor on until it falls to a safe level. Once you start driving and moving air across the stack, or the fans run for a few minutes, it cools the condenser down and drops the pressure to a safe level and allows the compressor to kick back on.