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Random intermittent problem with little to no air blowing thru vents...

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Fan motor is blowing, doesn't matter if recirc or not or if cold or hot selected, same outcome. This problem occurs every few trips and never close to a dealer. It clears itself usually after restart(s) of the engine or just waiting some time after an off/on cycle of the fan. When this occurs, it sounds as if a vacuum has occurred all of a sudden like you would hear in older cars when mechanical mixer doors would close or blend. After, the fan has a deeper sound like air is being blocked. I managed to grab video just after this problem occurs.

Video of problem

I took this to the dealer (still under warranty). They ran some diags, and of course since they couldn't reproduce it, they sent me on my way.
I already knew there were no historical codes or pid logging that indicated any problem because I checked before going to the dealer with forscan.
Anyone have a diagram of the internal mixer doors with condenser and heater core path? I'm convinced I can fix this because I would suspect it can only be a few components in the path of air that would affect both hot and cold, or maybe there is some sheet of paper that dislodges every now and again?. I've visually inspected the pathways from hood to fan, and fan to vents as far as I can get a light/mirror inside.

Any one experienced this? Any help would be appreciated.

Thanks
Scott
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That is bizarre. Thx for the video to demonstrate the issue. You might pull the glovebox down and open the cabin filter box to see if any air is moving there when it does this.
Another place to check might be the air intake for the cabin under the hood.

I assume you've played with all the adjustment settings with the same results. Intermittent problems are sure frustrating especially since most dealers aren't persistent enough to ferret them out.
 

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Discussion Starter · #3 ·
That is bizarre. Thx for the video to demonstrate the issue. You might pull the glovebox down and open the cabin filter box to see if any air is moving there when it does this.
Another place to check might be the air intake for the cabin under the hood.

I assume you've played with all the adjustment settings with the same results. Intermittent problems are sure frustrating especially since most dealers aren't persistent enough to ferret them out.
Thanks, hopefully it I can get it to happen when I have all the tools with me and can stop to isolate.
 

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Discussion Starter · #4 ·
I have determined this problem to be icing of the evap core. After reviewing the diagrams of the repair/service manual, the only common air path for both hot and cold air is the evap core. I also now recall seeing a lot of condensate coming from the drain tube when this happens. Makes sense that it happens 2-3 hours into a drive and then eventually thaws and starts working again. Also explains why the sound of the fan changes as it’s blowing up against a wall of ice. Now on to troubleshooting why evap core ices....low side pressure?, moisture in the system? Low side cycling switch? I’ve ruled out a clogged filter or drain tube.
 

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Yes, good call, an iced over core would block the air as you describe. In the meantime, when it happens on a residential or commercial AC, I've run the fan without cooling to thaw it out faster. This would be the first instance of a Transit AC freezing up that I've read about.
 

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Discussion Starter · #9 ·
Did you ever fix that problem???
I believe this problem was fixed (and by fixed I mean good enough that it hasn't happened again since the (temporary) fix?...yet). I did a few things. The effect was an iced over evap core. Both times this happened when it was raining heavily just prior. The trigger seemed to be rain each time and I believe each time the air intake was set to external. I installed a filter in the unit under the dash, double checked all of refrigerant pressures, vacuumed the refrigerant and extracted amount was well in range, leaked tested the system, no leaks. Added new refrigerant to reach target. Since then the A/C has been running with no problems.
 

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Since you can not turn the coolant flow to the heater core off, I am thinking the blend door directs heated air to the frozen evap core to de-ice it. Some people report the Ac blowing alternating hot and cold air.
 

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But I have same problem on AC and hot air
Computer controlled... It could be anything.
The wiring diagrams show 3 blend door motors, So there are three doors and any possible combination.
Many peoples problems are trace back to the ambient temperature sensor in the left front engine compartment.
 

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I also have these issues. 2017 transit 150. 3.7. No rear heat. Basic hvac controls.(3 knobs). Hot air out drivers side middle vent, but Luke warm air out of passenger side radio vent. This is like 30-40° f difference! And it seems to blow alot less force or cfm from the passenger side vent too. If I hold rpms 2500 it will heat up to match the drivers side but still lower CFM output.

There is a ford service bulletin on this issue. It has techs taking temp readings out each side and if different by 15° f or more they say the factory ford coolant has plugged up a heater core. It needs to b changed asap. My van has 70k miles thats it. Ive had new resistor twice and blower motor. And the replacement motor also got stuck and would not turn. Until I loosened the screws 1/4" and let it drop down. Ridiculous.
 

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Yep I’ve experienced the same thing on both of my Ford expeditions - a 2007 and my current 2018 which has the same engine and drivetrain.
It random but usually happens hours into a trip and alway clears itself up after a short period of time. I never sweat it and it alway pops back on.
I love this problem as it always fixes itself!
 
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