heater and a/c problems 1998 ford expedition.

Nov 17, 2005 1 Replies

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delvil 20 years ago

when heat is on and i speed up it switches to a/c and vis versa. you can here the heater box shut when it happens.

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Backyard Mechanic 20 years ago

you have a vacuum leak, or a bad check valve (vcv) in that line.

check all the way to the intake manifold tap.

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