When i use my heater or air conditioner on my 98 f150, it only blows air through the windshield defrost no matter what setting its on (floor, panel, ext.) Help! I can figure out what the problem is!

 

I'm pretty sure you have a vacuum operated system. This topic comes up alot so do a search for the detailed answer. But basically the problem is you have no vacuum and your HVAC system resorts to defrost when there is a complete loss of vacuum. Most likely one of your lines is disconnected or broken............

 

Inspect the small vacuum line that runs between the battery and the firewall.

It usually is the culprit (gets rotten from battery fumes).

 

I found the cracked Vacuum line, like you said it was the one behind the battery that runs into the firewall. Does anyone know where i can find a replacement??

 

Go to the parts store and buy a vacuum line connector/splice. A lot cheaper than buying and installing the OEM part.

 

I have an 02 King Ranch and it only blows through the defrost vents on Max. I can't find any broken vacuum lines. Any ideas?

 

What about the rest of the outlet positions?

 

The air conditio works properly in all other settings except for Max. Whenever it is on Max/auto it will only discharge throught the defrost duct. pan/floor and vent etc. discharges throught the proper ducts. when on pan/flr, the air discharges throught the floor ducts and the dash/panel ducts. this is what confuses me. If the vacuum pushes air throught these ducts on these settings, why not on max.....HELP!

 

Sounds like the EATC flaked out. Sorry.

 

this is what i found when i pulled the battery. ;just before the T the line coming out of the dash has been burned open, the other line comes out of the T to this box mounted to the battery hold down. I will fix this leak and see what happens.
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I also like to vacuum test the multi line connector that goes into the fender. Test it from both sides of the connector. Occasionally you'll find a small leak there. I've started watching it for some time, and have had to replace two of the lines. They get dried at the end and can crack open. You know you have the best seal when you get in your truck after it sits for a day, and there is still enough vacuum to move the mode door.

 

Here is the fix that I did. I used a vacuum line that sliped over the one that i cut out the bad spot. then i used hose clamps just to make sure it did not slip off. not too tight though. the under hose is kinda brittle.
checked the AC and it worked perfectly,.
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Great i don't feel so bad now knowing this is fairly common!

I have an 03 Screw and mine only blows AC out the windshield not matter what setting unless i switch to "vent" then it works in the normal vents.

I'll double check the vac lines and will pull the battery just to be safe....but are there other vac lines to worry about inside the cabin under the dash???

Also if that isn't it i'm guessing i may need to pull the EATC and follow the re-build instructions in the other thread i just posted in...........sux because i still need this ABS light to go off i've already replaced the rear abs sensor but no luck......now this AC thing

 

Hey all, I just bought a 1996 F250 today and have this problem. I checked the vacuum hose coming out of the "vacuum motor", but neither the hose nor the "motor" had suction. I'm not sure where the vacuum would be coming from. Can you guys help me out? Many thanks!!

 

vacume line is off or pinched check that first