AC stops blowing
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Junior User
Joined: Sep 2008
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AC stops blowing
1991 F150
4x4
standard cab
Nite edition
Auto
302 HO
AC is ice cold. Blows fine sitting still. Blows fine at slower speeds and lower RPM's. Stops blowing when you get faster and higher RPM's. I cant pin it down to a breaking point in speed or RPM's. I can still feel its ice cold it just wont blow it out.
Ideas????
Thanks!
4x4
standard cab
Nite edition
Auto
302 HO
AC is ice cold. Blows fine sitting still. Blows fine at slower speeds and lower RPM's. Stops blowing when you get faster and higher RPM's. I cant pin it down to a breaking point in speed or RPM's. I can still feel its ice cold it just wont blow it out.
Ideas????
Thanks!
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
Check the white vacuum line leading to the blend door near the passenger side of the evaporator case. That lines gets very brittle with age. Also trace back and test the vacuum line and reservoir mounted to the driver's side of the evaporator case. That little reservoir can crack allowing the blend door to slam shut under low vacuum conditions, this diverts all the air to floor/defrost mode in most cases.
Hotshot
Joined: Sep 2001
Posts: 11,958
Likes: 228
Like was already stated. There is a vacuum leak. It is likely that it is the white line under the hood on the passenger side in the corner on top of the heater box. This seems to be fairly common. It broke on mine too. It could also be the little T shaped check valve that runs from the heater box area over next to the engine.
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Junior User
Joined: Sep 2008
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THANK YOU ALL!!! It was the notorious WHITE vaccum line. Was dry rotted all to crap! easy cheap fix!
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Hotshot
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Junior User
Joined: Sep 2008
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OK so had to drive the truck to the alignment shop last night. Yeah still does it. Have any of you ever had the can that the white tube goes into go bad? I have checked all the other vaccum hoses I can find and all seem ok. The only other thing I can think of is maybe the T shaped connector.....ideas?
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Junior User
Joined: Sep 2008
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Dang... I have no idea where else to look. I have followed all visible hoses and even the ones inder the dash. What about the little can in the corner of the passanger side near the door under the hood. The one that the white hose that always dry rots goes into?
Fleet Owner
Joined: Oct 2005
Posts: 20,789
Likes: 1,753
From: Kentucky
If you are referring to the small plastic vacuum reservoir mounted on the blower case then yes it is a common point of failure in the HVAC vacuum circuit. Mine was cracked and covered in epoxy in an attempt to fix the same issue as yours. Of course the epoxy jacket did not help the problem.
I was fortunate to have a different vacuum reservoir setup for the emission equipment on my F350. Instead of a single chamber coffee can style reservoir mounted on the passenger fender my F350 uses a dual chamber plastic reservoir. The AIR injection system was removed so I snagged the unused section as a replacement HVAC reservoir.
I was fortunate to have a different vacuum reservoir setup for the emission equipment on my F350. Instead of a single chamber coffee can style reservoir mounted on the passenger fender my F350 uses a dual chamber plastic reservoir. The AIR injection system was removed so I snagged the unused section as a replacement HVAC reservoir.
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