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Discussion Starter #1
Hello, first post here - promise I searched all the threads...

Truck: 2014 F150 EB 3.5L FX4 with Dual Zone

Last week, temps dropped where I needed the heater. Set the thermostat to 71 and made it all the way to work before noticing the cabin did not warm up. I fiddled with the thermostat, cycling from hi to lo and the truck warmed right up.

Further diagnosing the issue, I have found that the air will be cool on lo and hot on hi with no steps in between for the numbered degrees between. When cycling from hi to lo you can hear the actuator move the door, followed shortly thereafter by blowing warm or cool air depending on the selection of hi or lo.

No matter the combination, starting at hi and moving to lo or from lo moving to hi, the numbered degrees make no impact on the temp of the air being blown throw the system.

The blower seems fine, blows as it should at different fan speeds.

The vent selectors work fine as well, defrost, front, and footwell.

Does this seem like a blend door issue to you guys? from the reading I have done, most have other symptoms (clicking or stuck at a certain temp)

Looking forward to the help, I appreciate it!
 

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There is some degree of intelligence to the HVAC system. My manual system set to hot and high fan will not blow at max speed until the engine warms up enough to actually heat the cab, then automatically ramps up the fan to the high speed setting on its own. Perhaps the same issue with yours and only setting it to max temp overrides the smarts trying not to blow cold air on you. Maybe hunt down the coolant temp sensor that feeds the brain of the HVAC system. I don’t think it’s a blend door. The sensor may be unique to the HVAC system and be in the heater core coolant line, on the heater core itself or in the air box by the heater core. It may be giving false readings. Hypothesis only.
 

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You may have already checked your coolant level but I figured its worth a mention. Last month when my heat didn't come on I then realized my coolant level was low... Which then lead me to discovering I had the inevitable and costly to repair coolant line fitting leak on my driver side turbo. And now that I repaired the driver side, the passenger side has begun to leak two weeks later. I'm guessing the coolant pressure found the next weakest link in the system. I'm at 60k miles, 2014 XLT crew cab. Anyhow, best of luck with yours.
 

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Thanks for the replies. I took the opportunity today to tear into the dash to work on it. My best guess was that it was the lower blend door actuator, since it is the actuator that’s controls temp for the dual zone trucks.
Got the trim tore out and noticed that my little one had stuffed all my dimes into the cracks and crevices. One of those crevices was the vent in the dash for the in cabin temperature probe. My little one stuffed a dollar-twenty worth of dimes in there. I pulled them all out and voila it works as designed. Temperature blends as it should.
my guess is that the dimes were shorting the circuit board as the contacts are exposed.

thanks again for the replies guys.
 

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Discussion Starter #5
You may have already checked your coolant level but I figured its worth a mention. Last month when my heat didn't come on I then realized my coolant level was low... Which then lead me to discovering I had the inevitable and costly to repair coolant line fitting leak on my driver side turbo. And now that I repaired the driver side, the passenger side has begun to leak two weeks later. I'm guessing the coolant pressure found the next weakest link in the system. I'm at 60k miles, 2014 XLT crew cab. Anyhow, best of luck with yours.
goodluck with your fix!
 

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Thanks for the replies. I took the opportunity today to tear into the dash to work on it. My best guess was that it was the lower blend door actuator, since it is the actuator that’s controls temp for the dual zone trucks.
Got the trim tore out and noticed that my little one had stuffed all my dimes into the cracks and crevices. One of those crevices was the vent in the dash for the in cabin temperature probe. My little one stuffed a dollar-twenty worth of dimes in there. I pulled them all out and voila it works as designed. Temperature blends as it should.
my guess is that the dimes were shorting the circuit board as the contacts are exposed.

thanks again for the replies guys.
Haha

Great story, and I bet relief that you didn't have to tear any further.

Sent from my SM-N950U using Tapatalk
 
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