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Heater changes to defrost under throttle

sgoulden76

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Joined
Aug 7, 2022
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Location
Nova Scotia, Canada
Vehicle Year
2010
Make / Model
Ford Ranger
Transmission
Automatic
My 2010 4cyl auto Ranger has shifting issues where when I give it throttle say to pass someone or climb a hill it doesn't shift. It'll sit at 4.5k to 5k.
When it does this the blower switches from the console to the defrost. I let off the throttle and it'll shift and the air returns to the correct vent
My thought was some kind of short or ground issue with the TPS.
Thoughts?
 


RonD

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Jun 2, 2012
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Location
canada
Vehicle Year
1994
Make / Model
Ford
Transmission
Manual
Switching to Defrost vent is a Vacuum issue, not related to transmission shifting

The defrost, panel and floor vents are vacuum operated
Defrost is the default(low or no vacuum) selection
On the passenger side front down low, of the engine bay, is the Vacuum reservoir "ball"
It has a vacuum line to the engines intake manifold
It has a vacuum line thru the firewall, below heater fan, and to the dash selector switch

Most common place to start when you have this common issue is the vacuum line from the "ball" to the firewall in engine bay, hard plastic black line, looks like a wire
Anywhere near exhaust system this line can crack or melt, so system can not hold vacuum long, when you accelerate vacuum in the intake drops to almost 0, if there is No Reserve, then vents change to Defrost until vacuum returns to intake manifold

The "ball" can also crack, not common but can happen, its behind the inner wheel well in front of passenger side tire


Its a long shot but possible that there is a vacuum leak on the engine side of the "ball", do you have a higher than normal idle?
Computer uses a few sensor to calculate engine LOAD and engine load is used for when to shift gears
Calculated engine vacuum is part of the load on engine, lower vacuum = higher load
Although I would guess these two things are unrelated
 

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