ac problems

[champpydog]

I have a 2002 F250 andd I have been having this weird problem with my ac. When I accelerate the ac stops blowing out of the vents and blows up the windshield like the defroster is on, then when I slow down itgoes back to the vents. What the hell? Is it a relay or something else?

[megawatt00]

I'm not 100% sure on this one, but there is a possibility that the blower motor isn't running. Maybe when you slow down it's takeing the path of least of least of least resistance. This will bump you back to the top and some one else will chime in.

Oh and by the way WELCOME TO FTE!!!!!!


I also posted this reply in the super duty forum for ya.

[projectSHO89]

No, it's the common vacuum leak.

Click on SEARCH and enter "+vacuum +defrost" for numerous discussions, most of which ironically, are in the Heating, Cooling, and Air Conditioning section....

Steve

[NumberDummy]

Originally Posted by champpydog

I have a 2002 F250 and I have been having this weird problem with my ac. When I accelerate the ac stops blowing out of the vents and blows up the windshield like the defroster is on, then when I slow down itgoes back to the vents. What the hell? Is it a relay or something else?

This could be the problem..and it sure wouldn't be the first time one failed.

F6SZ19B888AA .. Air Conditioning Vacuum Selector Valve Assy. (Motorcraft YH-1450)

MSRP: $24.46 / ftepartsguy.com price: $14.09

This valve mounts to the back side of the A/C heater control panel-this is where all the vacuum lines connect.

When you operate the lever on the control panel, the valve opens one door in the plenum chamber, and closes another.

The little darlin' is plastic and over time, it develops cracks, which causes the valve to go haywire.

One minute air is blowing out of the defroster, the next, it's blowing out somewhere else.

[champpydog]

Thanks for the input guys....I will check for vacum leaks and check the vavle assembly....I'll let you know how it works out.

[Franklin2]

The engine has no vacuum when the throttle is open wide, such as during acceleration or pulling a hill. I would think your newer truck has the same setup as the older ones, with a check valve and a vacuum reservoir.

The main vacuum line for the HVAC comes from a tree on the firewall, and goes through a check valve. After the check valve, it hits a tee which branches to the vacuum tank or reservoir. The other part of the tee goes on into the firewall and is the vacuum supply for the HVAC. When you accelerate, the check valve stops the vacuum from being lost, and the HVAC uses the vacuum stored in the reservoir till things settle down and the engine has vacuum again.

[NumberDummy]

Originally Posted by Franklin2

I would think your newer truck has the same setup as the older ones, with a check valve and a vacuum reservoir.

Exactly, cars included.

For every one of those check valves, or reservoirs (we called 'em coffee cans) we sold, we sold 10 of those vacuum selector valves, that's why I suggested it.