My dodge caravan is losing all its freon. I hear

Well the hissing sound could be a vac leak or the freon flowing thru the system.
Someone needs to check the freon charge in the system with a gauge and the electrical circuit to the compressor clutch.

Have someone check the freon charge in the system with a gauge, and voltage to the ac compressor clutch.

needs regas aswith the hissing it has a leak

probably the evaporator core under the dash leaking

Blower motor not working , do you feel an air movement out the front vent's ? ( I just did a self-recharge on my refrigerant ) Too much of a charge can work as not enough of a charge . The back or AUX HVAC system works off the same compressor as the front . The noise you hear is just refrigerant moving through the system . Temp .door actuator maybe . Your best bet ,mite be to take to a qualified repair shop. Doesn't sound like you know about automotive A/C systems . .

Just a suspicion: hissing noise comes from failed/jammed/malfunctioning motor to move the door
in the ducting to route heated air to the hoses/ports for "heater" and "defrost."
Problem: failure of motor/linkage to heater/defrost selector door under the dash on the passenger side.
Also sounds like you have not blown fuse to this selector door.
Also - hissing noise could be air being forced against the closed door (which should be open) - in this
case, you'd want to check the fuse to the heater/defroster actuator door.
The rear heater works since its function is not related to the operation of the front heater/defroster.

probably the evaporator leaking the noise may be just the freon going through the system, you have to remove the entire dash to access the hvac box to remove it to replace the evap seek a professional

you dont have to seal line as long as you are going to b putting back together, however u will have to have ac vacuated, and recharged, normally 1oz oil for everypound freon hope all this helps

may have bad idle air control valve,is check engine ligt on? also check for vaccum leaks/ you will hear hissing sound.

change the evaporator coil on the a/c. As for the window, I have the same problem and I was told it is with the motor in the door.