Vacuum Troubleshooting
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Freshman User
Joined: Feb 2004
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From: Crestview, FL
Vacuum Troubleshooting
I have a '94 F-150 and could use some help troubleshooting what I believe to be a vacuum problem. When operating the A/C everything works fine until I put the engine under a load. When the engine is under a load the A/C will stop flowing out the vents in the dash and will switch to the defroster. I think the problem is some type of check valve but don't even know where to look. Any ideas?
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The default (without vacuum) for the A/C system is the defrost position. When under a load your engine looses vacuum supply and the air comes out the defrost vents. So, you have a vacuum supply problem. I have seen the supply lines get porous, a smoke machine works great for this, or if somebody you know smokes, try having them blow smoke into the vacuum supply lines and fix where it comes out. Check supply to reservoir, and all lines going into the cab. As I recall, the white nylon line is prone to porosity.
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Freshman User
Joined: Feb 2004
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From: Crestview, FL
Thanks, I should be able to track it down tomorrow. I was hoping this would turn out to be a common component that goes bad on the 94's. Getting old and it hurts to think in the troubleshooting mode....
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Freshman User
Joined: Feb 2004
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From: Crestview, FL
Didn't need to look too hard at the white vacuum line to tell it was bad. I touched it and it fell apart in my hand. Replaced it with some 5/32 rubber vacuum line and it works great. Thanks for the info, it's nice to have the A/C work right when I step on the gas.
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Murf's
I am haveing a simular problem on my 96 f-150.It seems the switch that directs the vacuum to the proper vacuum switch is leaking. I can hear the air leaking from inside of the switch. I will order a new one tomorrow. It is easy to put in.