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Discussion Starter #1
My brother has a 2013 F150 EcoBoost 3.5L crewcab 4x4. The truck just hit 75,000 miles. He has the ford dealership rotate tires and changes oil every 5000 miles.
The fan that cools the engine kicks on as soon as he cranks the truck. Fan cuts on immediately when he first cranks truck that day. It used to kick on after motor built the temperature up. Last week the air conditioning evaporator sprung a freon leak. He put freon and leak seal in it because ford dealer wants $1700 to replace evaporator. Ford says they have to remove dash to replace evaporator. Just wanted to throw out the only issue he has had with truck.He is original owner.
Any ideas on why the fan cuts on immediately before truck builds temp?
 

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Normal, its part of the starup sequence depending on environmental factors and HVAC setting.
 

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May have over filled the freon. My buddy overfilled his once and the fan acted all funny for a few days til he drained out enough.
 

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Agree that it’s probably something to do with the ac. Fans are usually triggered by a pressure sensor in the ac circuit
 

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update op?
 

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I overfilled the Freon on my 5.4 expedition and it did the same thing.

That was an expensive lesson.


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Discussion Starter #10
I'm gonna have my brother recheck the freon level. I understand it could be a low/high pressure switch causing it.
 

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R134a is very sensitive to temperature changes, and thus its pressure (when contained inside the AC system) is dramatically affected by it's temperature. In short, high temperature = higher pressure, low temperature = lower pressure.

Our engine ECU can read the pressure of the refrigerant via a pressure transducer. When the pressure is excessively high, the ecu doesn't know that the system was overcharged, so, it turns the fans on to flow more air through the condenser which in turn cools the refrigerant faster which in turn will lower the refrigerant pressure.

Tell your brother to stop messing around with AC systems - not only did he overcharge the system, that stop leak crap he put in there often causes more problems than it solves. His $1700 repair will probably cost more like $2500 to $3000 once the dealership disassembles the system and finds it full of goo.

PS: I am a professional mechanic by trade and I am AC certified
 

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Discussion Starter #12
R134a is very sensitive to temperature changes, and thus its pressure (when contained inside the AC system) is dramatically affected by it's temperature. In short, high temperature = higher pressure, low temperature = lower pressure.

Our engine ECU can read the pressure of the refrigerant via a pressure transducer. When the pressure is excessively high, the ecu doesn't know that the system was overcharged, so, it turns the fans on to flow more air through the condenser which in turn cools the refrigerant faster which in turn will lower the refrigerant pressure.

Tell your brother to stop messing around with AC systems - not only did he overcharge the system, that stop leak crap he put in there often causes more problems than it solves. His $1700 repair will probably cost more like $2500 to $3000 once the dealership disassembles the system and finds it full of goo.

PS: I am a professional mechanic by trade and I am AC certified
I agree with you 100%. I am a HVAC tech and have dealt with freon every day for the past 20+ years. I'm not a fan of leak stop in a system. I told him it contaminates a system. It clogs orifices and other metering devices in a system. Sometimes people have to learn from there mistakes. Instead of learning from others experiences.
 

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I have 2014 f150 ecoboost and when I step on the gas kinda hard sounds like heater starts blowing full blast???
Cool story. Mine doesn't make a lot of sound but it sure moves out fast!
 
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