No AC lines in the cabin
They are only in the engine bay, the closest to the cabin they get is the Evaporator in the heater box in engine bay
But its an open hole from there to inside the cabin thru the firewall
If AC is "icy cold" then it may be low on fluid, kind of funny that it get colder when low on fluid but then it will stop working when too low
Turn the blower/fan off just to confirm its not the noise you hear
Could be noise from dirty filter or orifice tube inside AC system
More than you need to know but not complicated, lol
The noise can be from how all AC systems work, vehicle, home, refrigerator, or freezer
AC works by compressing a fluid to a high pressure and then releasing the pressure slowly
Compressing the fluid makes it hot, releasing the pressure makes it cold
And that's all there is to it, really
Anyone who has used an air compressor has noticed this
Compressed air in the tank, and the compressor are hot, but when you use the compressed air what comes out is COLD, high pressure to low pressure causes a temp drop
The Fluids they use for AC can get really hot so can also get really cold
Vehicle AC compresses the fluid by engine power(this is called the "high pressure side"), and it has a high pressure switch that will shut off the compressor once the pressure is high enough
At the Evaporator is a filter and an Orifice tube, just a small tube with a hole in the end
The size of the hole in the Orifice tube decides on how much pressure/fluid is released, so they come in difference sizes, FYI
As the high pressure fluid flows out into the low pressure Evaporator it gets very cold, 36-40degF(you DO NOT want a lower temp or moisture in the air will freeze on Evaporator's fins and clog it up)
The blower/fan blows ALL the air thru the Evaporator and into the cabin, heater core is in the cabin, the COLD-HOT control routes the air coming in either around the heater core(COLD) or thru the heater core(HOT), and anywhere in between(heater core is 180degF, so heater core blows away anything AC can do, lol)
Once the fluid has passed thru the Evaporator it will circulate back to the compressor(this is called the "low pressure side") and there is a pressure switch in this side, low pressure switch, it will turn off the compressor if pressure is too low, not enough fluid, which can burn up the compressor if it runs out of fluid
The system is OPEN internally, no shut off valves
When you turn AC off the high pressure fluid still flows to the low pressure side until BOTH sides are equal pressure, same when you shut off the engine/key, pressure keeps flowing until it equalized
As fluid runs low the pressure difference from the high pressure side to the low pressure side gets bigger, so temp drops even lower, "icy cold" and it will even cause real ice to form in the engine bay on the AC pipes going into Evaporator, which means ice is also forming inside heater box on Evaporator fins which WILL block air flow from the fan into the cabin
So if the noise is pressure related it would be there until pressure is equalized
Could be dirty filter or clogged/failing orifice tube
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