A/C blower output
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Senior User
Joined: Feb 2000
Posts: 390
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From: South East Alabama
A/C blower output
When I go up a slight grade in my 96 F150 300/5spd with the A/C blowing out the dash it will cycle and blow out the defrost and floor vents. When I crest the grade and let off the throttle slightly the A/C returns to blow from the dash.
I was just driving my Dad's 96 F150 302/E4OD and we noticed his does the same thing. Is this normal operation? Or do we both have vacume leaks? Has anyone else had this problem?
I was just driving my Dad's 96 F150 302/E4OD and we noticed his does the same thing. Is this normal operation? Or do we both have vacume leaks? Has anyone else had this problem?
Senior User
Joined: Apr 2000
Posts: 188
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From: Latrobe USA
A/C blower output
That's fairly common, the controls are sprung to the defrost and vacuum to pull anywhere else. the manifold vacuum drops when you're on the throttle and your defrost comes on. If there's actually a problem....I don't think there's a fix.
Anyone know?????
Anyone know?????
Postmaster
Joined: Jul 1999
Posts: 3,172
Likes: 4
A/C blower output
Shotgun ,
Depending on the A/C , Heater combo you have , there are a few different setups , there is a vacuum motor that controls the air flow to the defrost / floor that is most likely the problem . Either its leaking down or its vacuum line is leaking . All the control doors to direct the air flow are vacuum controled . Going up a hill the engine vacuum is reduced so in turn the vacuum motor is also not getting full vacuum . Best thing to do is trace all vacuum lines from their source to the vacuum motor . This may involve some disassembly . If you have the air selected for the vents it should stay there regardless of engine operation .
Paul
Depending on the A/C , Heater combo you have , there are a few different setups , there is a vacuum motor that controls the air flow to the defrost / floor that is most likely the problem . Either its leaking down or its vacuum line is leaking . All the control doors to direct the air flow are vacuum controled . Going up a hill the engine vacuum is reduced so in turn the vacuum motor is also not getting full vacuum . Best thing to do is trace all vacuum lines from their source to the vacuum motor . This may involve some disassembly . If you have the air selected for the vents it should stay there regardless of engine operation .
Paul
Senior User
Joined: Mar 2000
Posts: 360
Likes: 0
A/C blower output
There is a one way check valve under the hood, in series with the vac line to engine. Also a vac res. on the side of the A/C evap. under the hood. The vac. res. should hold vac on the dash controls when the check valve closes due to lower (less) vac in intake manifold when engine is under load. If check valve leaks, or leak in res. or hoses, then stored vac will be lost, and not hold the controls in the set position.
