Strange Air Conditioner symptom

[Richard McAlister]

Not really a problem, more of a curiosity. Three times in the past few months (today the last), the the A/C air flow has spontaneously changed fron the dash vents to the defrosters for about 8 seconds, then back again. This happened on straight, level roads without acceleration. Truck has the dual zone digital controls. Air stays cold.

Any thoughts?



:driving:

 

[Joe Marek]

This happened on my old ranger, it got progressively worse. Turned out to be a small vacuum line connected to the AC system was broken in the engine compartment.

 

[Gavin Allan]

Vacuum line check valve probably leaking. You can test it quickly with a Mi-T-Vac. Very cheap and easy to replace.

 

[Richard McAlister]

Thanks for the replies,

I couldn't see any leaks under the hood, where might the vacuum line check valve be located?

thanks