Air Vents Cutting Out in '03 CV

Hi All, My air vents sometime switch flow to defrost vents. This seems vacuum related as is more likely when going uphill and gets restored under
lighter load conditions. Any idea where to look for problem? 2003 Crown Victoria.
Thanks, Kent
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Is this a new behavior in a car you've owned for quite a while or is it a problem you've just noticed in a car that you recently bought? Or bought since winter began and you've been using the defrost vents continuously since you acquired it?
Does the A/C compressor, if it was engaged, cut out and does the air from the defrost vents come out hot?
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I have had this car for a while and is new problem and only happens occasionally. If the AC compressor is running it will still be cold when dash vent switches to defroster port. I am thinking a vacuum hose may be leaking as engine load effects problem., the question is where?
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We had a Ford with a similar problem. The dealer never could reproduce it. Which was aggravating, because, once the car was warmed up, driving up any hill would exhibit the symptoms. In our case, whenever this happened, the A/C would cut out and the heat would come on (this was very unpleasant in the summer).
Of course, why would engine load affect interior ventilation port selection? This problem is sort of crazy. However, your idea of vacuum leak sounds like as good a place as any to start. Are you getting decent fuel economy?
Here's a thought... have you checked your coolant level? Maybe it's not so much engine load as having the car pointed up hill? If you had a coolant level/sensor issue, maybe tipping the car uphill would make a difference? Of course, I'd expect an idiot light in that case. Maybe it's something really weird, like the idiot light or sensor is wired incorrectly and the engine management thinks something other than coolant is misbehaving.
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"DH" wrote: (2003 Crown Victoria)
My air vents sometime switch flow to defrost vents. This seems vacuum related as is more likely when going uphill and gets restored under lighter load conditions. Any idea where to look for problem? ____________________________________________________________
I had the same problem with two older cars - a 72 Olds and an 86 Buick. In both cases it was a leaking vacuum distribution valve. This was a valve behind the dash that connects to engine vacuum and distributes the vacuum to vent flaps and heater valves in accordance with drivers settings.
In one case, I installed a replacement valve which worked fine. In the other case I just lived with it, knowing things would settle back after I let off the gas.
If you can find the valve, try pushing all the vacuum lines on firmly, in case one has come loose.
Good luck.
Rodan.
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In this case, the valve is actually mounted to the rear of the air control. It does sound like a loss of vacuum as "Defrost" is the "default" no vacuum state.
I would check the lines at the back of the control head and at the vacuum manifold under the hood. It will be a block that will have 4-5 vacuum hoses coming from it. I would try putting a vacuum to it. If it holds, then your valve on the control head is fine. You need to find the leak leading between the intake and that manifold you just disconnected the a/c vacuum line from.
If it dont hold, then you need to think about tracing that vacuum line all the way back to the control head to find the leak. If you cant find one in the line, it will be the valve on the back of the control head.
Ford Tech
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