Heater Problem

I have a 92 F-150 with a heater (or might be a vacuum problem). When I drive faster than a certain MPH (about 55) then the air that is coming from the heater switches from blowing on the floow (where I want it) to blowing
on the windshield (the defrost setting). I have no control over this other than lowering my speed. No combimation of settings seems to make a change (other than off).
I am pretty sure this also happens when the air is cold, but haven't tested with the a/c as I don't use the a/c.
Anyone have any idea what I can fix? I would really like the air to blow here I want it to blow.
Thanks,
Joe.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

You have a vacuum leak somewhere. The engine has less vacuum at higher speeds, and the vacuum switch isn't getting enough to operate properly.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
qwest wrote:

long time.. probably a vacuum line leaking on the back of the heater... when you speed up you loose vacuum(just like the old time vacuum controled windshield wipers would stop when you speed up and you would have to ease up on the gas to let the wipers work so you could drive)... your vacuum system is probably controling the heater and you either have a leak or bad vacuum motor??? hope this helps.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It is most likely a vacuum leak. Look under the hood first. The heat of the engine will cause lines to harden/fail.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
All-
Thanks for the info. I will take all the suggestions and look to see what the problem is.
Joe.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.