I hate it when I type a long, detailed post, and it does not show up.
Short (for me) description of vehicle dash ac starting with the compressor (pump)
Gas (vapor) is compressed, causing it to 1: Get very hot and 2: Turn into a liquid, this is then pumped, through lines to a CONDENSER which is a high pressure radiator usually located in front of the vehicle's raidator. Here it sheds much of the heat and is pumped through lines, still as a liquid, to the EVAPORATOR, which looks like a high pressure heater core, only it's a cooler core, and is often next to the heater core. Somewhere in this line there is a can, called a dryer or accumulator, it may have a glass eye called a sight glass. During normal operation this sight glass should be about 1/2 full of liqud and the inlet and outlet fittings on the "can" should be about the same temperture (NOTE: test with caution HOT is one of the tempertures)
In the Evaporator the liquid turns back to a gas, which makes it very cold, it picks up heat from the air passing over the evaporator's outside, it it then returned back to the pump for re-compression and the cycle starts again.
Possible problems. If there is not the right amount of coolant in the system, then the liquid will turn to gas either before entering the evaporator or after leaving, thus not cooling the right things. If you have no expierence with fixing this professional help is recommended. I have fixed it many times and have the tools, but I don't do it professionally.
Next we have the air handeling system This may be simple or complex. In the simplist system air enters your intake grill (on cars this is normally at the bottom of the windshield, a very stupid place to put it, motor homes it can be in many places) and then passes first over the Evaporator and then over the heater core and then to a diverter assembly that sends it to either the Dash vents, floor vents or defroster vents (windshield) or some mixture thereof.
This is the simple one,,, A much more complex system uses multiple diverters
First there is the "Source" divereter (Recirculate air from inside the car, or take in fresh) normally a vehicle with AC has this option somewhere (MAX ac is all recycled air, normal is mixed, and heat is all fresh air, unless you have a manual source selector like my wife does)
Then we decide if we are going to heat, cool or bypass
Then we decide where to deliver (Dash, floor or windshield)
This system may be controlled by cables off sliders or knobs on your dash, or it may be controlled by vaccume solonoids which are in turned operated by either the dash controls or thermostats.
My guess is that the problem is either in the AC charge (amount of coolant) or in the vaccume controls for the air flow.
That said, I have symptoms simular to yours, I can clearly hear the pump cycle on and off when SWMBO changes the switch position, however the dealer told me it was a low pressure sensor....
In my case, warranty applies