There could be several reasons why your AC turns on but no air is coming out. It could be due to a clogged air filter, a malfunctioning blower motor, a blocked air duct, or a problem with the compressor. It is recommended to have a professional HVAC technician inspect and diagnose the issue to determine the exact cause and provide the necessary repairs.
i hear a noise every time i turn the rear ac
If the ac is on and no cool air is coming out you may not want to turn the ac on at all. When you put the ac on, verify that the compresor is actually coming on, if you can see it spiining whne turned on, you may have low refrgernet in the sytem or a blockage. It is best to have it look at. If it is run when it is not working properly, you can severly damage the ac sytem if its being run when somthing is wrong.
you would turn the temperature down for cooler air temperatures in a car, in a house the air temperature coming out the vents does not change based on the thermostats set point
most likely it is out of freon
is it because of a lack of vacuum pressure?
You can tell if your AC is frozen by checking for ice buildup on the coils or pipes, reduced airflow, warm air coming from the vents, and unusual noises. If you suspect your AC is frozen, turn it off to allow it to thaw and contact a professional for assistance.
replace? why not fix it?
The temperature difference between the air coming out and the air going back in.
Actually you can't, because an ac unit does not cool the air, it removes the moisture from the air that in turn cools it. An ac unit is actually a de-humidifier.
Many auto manufacturers engage the AC compressor when the defroster is used because the AC system also dries the air. In a humid environment the drying effect of the AC can help keep the windshield clear.
This usually happens because the AC is set to heat and not cool. If it is set to cool then get it checked out by a qualified AC technician.
Have you checked it's switched on?