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where do I add freon to my air conditioning unit on a 1997 chevy truck?
no
to the low side
R134a
You can add Freon to your 1999 Chevy cooling system through the low pressure port. Connect your Freon bottle to the low pressure port and release the Freon into the system.
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You have the drain the lower radiator hose, 6.0 liter do not have a drain valve.
Which do i hook to to charge the freon in a 2004 ford expedition
Freon is a very touchy thing to work with. The EPA bans its release into the atmosphere, so only experts and professionals know how to add and subtract Freon from the car safely. Take your car to a mechanic or a Chevy dealer for this.
The schrader valve on the low pressure side of the system.
This is what I did for my Chevy prism 2000, it works fine: http://www.id-usa.com/how_to_recharging.asp