I'm generally familiar with auto A/C systems and have been working on them since 65 but I have a very specific question. 2004 Expedition w/5.4 L engine, on hot days and at low speeds (in heavy traffic say) the system will stop cooling. I know that many systems have a pressure sensor on the high side that will disengage the compressor when pressure gets past a preset point to protect system components. Does any one here know whether or not this sensor is particularly prone to failure on 04 Expeditions? Has anyone here had this problem with this particular vehicle and if so how did you handle it. This truck has the dual A/C system and the problem occurs no matter what the system configuration is, given high ambient temps and low engine speeds.