Odd behavior in HVAC system.

[sledboy]

There is something happening to our HVAC system that doesn't seem normal. While we are cruising down the road at 70ish mph, we will periodically and suddenly get a very high volume of air flowing through our vents. A quick check to the fan speed shows it is still set on 1. But the amount of air flow is equivalent to the fan being on high.

I believe there is "valve" of sorts (not sure what it is called) in the ducting system that opens and closes to allow outside airflow. When the valve is open, the higher the vehicle speed the higher the air flow through the vents. The odd behavior is that this "valve" seems to randomly open and forces a dramatically high amount of airflow through the vents. Playing with the buttons and turning the recirculation button on/off will usually return the system back to normal. Then 5 to 10 minutes later, it happens again.

Is anyone else experiencing this behavior?

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[acnp2022]

I have heard others talking about it and I have experienced it too before. Doesn't happen that often, but on a longer shift it does happen

 

[Ksjrb03]

The term your looking for is blend door.

 

[sledboy]

The term your looking for is blend door.

Ah, thank you. So my guess is that the blend door randomly opens and allows high air flow through the vents when the vehicle is traveling at highway speeds.

 

[PapaWE]

If you are in auto cool mode then it could be sensing a higher temp and trying to compenate

 

[WuNgUn]

The term your looking for is blend door.

Blend door is the actuator for hot/cold I believe... Damper door is outside/recirculate

 

[da_jokker]

Pay attention as to if it correlates to your throttle. I had a weird issue like that (not a Bronco) and turned out to be a leaky vacuum line that operated the hvac doors. On throttle would lose to much vacuum and the door would open, off throttle there was enough vacuum to overcome the crack in the line.

 

[LAbronco]

I’ve been driving a dealer demo for a week. It randomly does this also. It’s a base and doesn’t have a auto feature that I have seen.

 

[604Bronco]

trying to compenate

You mean, we didn’t all buy Bronco’s with Sasquatch package to compensate for something??!

 

[M&M Beer]

Isn't there a damper on the grill that might be modulating?

 

[kurkowski41]

I wonder if, since you're on the lowest fan speed, it's sensing the evaporator start to freeze up so it's increasing airflow to prevent that from happening.

 

[Bob 07064]

Ah, thank you. So my guess is that the blend door randomly opens and allows high air flow through the vents when the vehicle is traveling at highway speeds.

The blend door is to seal off the heater from the ac and vice versa when one or the other is not in use. The air flow thru it is controlled by the blower fan. Maybe that's the issue... Some how it surged?

 

[MileHighCitizen]

This truck is turning out to be a peice of shit. Im starting to feel dumb for staying on board with my order.

 

[WillyB]

I have the same issue. No correlation to speed, throttle, temp, or anything. Sometimes barely blows air and sometimes blasts full on Speed 1. For now I am simply keeping a list of things and will have it all checked out when I go in for my first oil change.

 

[Wanted33]

Just to throw this usless bit of information out there. My '20 Ranger with the manual system has so many little odd things going on I won't try to list them here. But, just a readers digest version is the little HVAC lights come on when I start the truck that I know I haven't pushed. Sounds like Ford is using the same system in the Bronco.

BTW, I haven't taken it in as I know I'll hear the dreaded words, "They''ll do that".

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