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rock 5/13/2010

2002 Ford F-150 King Ranch 8 Cyl 5.40L

Body & Interior

Air (AC) comes out of the defrost vents when I am loading the engine or going up hill etc.

When i am just cruisin down the hwy and am keeping up with traffic the AC blows normal, but when I go faster or put any strain on the engine it tends to blow out the defrost.

1 Answer


Your a/c in your dash works on vacum, more you give it gas, less vacum at the port for your A/c ducts.
You may look and see if you have a vacum line leaking or half off. Be on the Pass. side around the windshield wipers
and the fan motor area. Some have a vacum ball or canister to save vacum for just times like this. Do you hear
a hiss under your dash while sitting still at a red light>??? May be under there. High mileage cars don't make
as much vacum as newer ones, and you can get a one way valve and put in line to help stop this. It sucks one way,
and won' t let the vacum go back the other way, and it helps.. Look for a leak first, and listen for a hiss while truck
is running and all is quite, may have knocked something loose if put in a new radio also.


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