The entire system does not get replaced. That would cost thousands of dollars in time and parts. Instead, a problem must be diagnosed, then only the defective parts are replaced. What problem or symptom led up to this repair?
There are three things to be aware of. First of all, to save time on the assembly line, Ford uses AC system hoses that have some quick-connect fittings that do not require tools. Those have a miserable history of leaking, so expect to need to have the system recharged every two to four years. That can be done without replacing other parts.
Second, when parts are replaced that require the refrigerant to be recovered, it is customary to replace the receiver/drier if your mechanic is conscientious. That has a filter in it, and it is able to absorb and hold up to about ten droplets of water. Moisture in the system can be deadly to metal parts, and it can cause intermittent loss of cooling. When parts are replaced, the system must be pumped into a vacuum for a half hour before the new refrigerant is pumped in. In a vacuum, water boils at seventy seven degrees, then the vapor can be pumped out. Water combines with refrigerant to form an acid that attacks the metal parts and can lead to leaks. Also, if a drop of water manages to circulate through the system, it will freeze at the control valve's orifice, and block the flow of refrigerant. The cooling action will be lost until that ice melts, and that typically takes from a half hour to an hour. The clue to this is found by observing the test gauge readings. The system will appear to be working properly, then, when the problem occurs, the high side pressure will go too high, and the low side will go so low, it might cause the low-pressure cutout switch to turn the compressor off.
The third thing is not exactly related, but is worth mentioning when looking for clues. Chrysler used a sight glass in the receiver/drier for many decades, to tell when the system is fully-charged. Without that, the only way to know if the correct amount of refrigerant is in the system is to pump it into a vacuum, then pump in the exact measured amount. Too much or too little refrigerant can cause performance problems. Ford began using a sight glass too in the 1980's, but they do not have the same value. When the correct amount of refrigerant is pumped in, and the system's performance is perfect, there will still be vapor bubbles in the sight glass. No matter how much you continue to add, those bubbles will never go away. If you are familiar with that sight glass, do not think the system is low on charge based on what you see in it.
I have never run into a receiver drier making noise, but if you have verified that is the cause, my suspicion would be there is a sharp point of something that is causing the noise when the refrigerant flows over it, similar to the singing of a bathroom faucet. You can confirm that by listening to it with a stethoscope. There should be no problem getting that replaced under warranty, then, given the continuing problems, I am sure the mechanic is going to spend a little extra time pumping out the moisture from the system.
If the problem of intermittent loss of cooling continues, the next suspect would be the heater controller. High-end cars usually come with fancy computer-controlled automatic temperature control systems, and those cause a real lot of problems. That can become an involved diagnosis for an electrical specialist.
Friday, April 7th, 2017 AT 7:20 PM