A gas particle analyzer, sometimes called a Freon Leak Detector; depending on how small the traces are.
The Freon probably needs to be recharged. Any repair shop should be able to do this. They should also test the system for leaks to see why the Freon leaked out to begin with.
You are out of freon. Go to your regular mechanic and ask him to test and fill your system.
freon is just a brand name
Answering "Where do you add freon to your air conditioner in your ford ranger?"
The air conditioning Freon capacity for your 1999 Chevrolet Tahoe is five pounds. The manufacturer recommends that you never overfill the air conditioning Freon.
To know when an air conditioning unit (non-window unit) needs to be charged (needs freon), it will not cool properly or you can test it with the appropriate gauges (see related link below).
Your 1993 Ford Taurus air conditioning system has a Freon capacity of 5.5 pounds. You should never overfill the air conditioning Freon.
If you are talking about removing the freon in the a/c system then you will need a freon reclaimer.............
NO
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Whenever the freon filled system is opened air gets in and to remove it you attach a vacuum pump and empty the entire system before adding replacement freon. HOWEVER, if you have already added freon and do not have access to a vacuum pump, just bleed out the air and freon at any convenient point, the freon will push out the air leaving only freon vapor, then recharge with new freon and you will be air lock less!
low on freon