jennkent5454

it has to be a vacuum leak some where, where should i look first? under hood, under dash? i just had a used engine installed so im betting they missed a vacuum line somewhere

lifted98_f150

are you sure its not a bad switch?

trusourud

I'm very interested! I would love to find out more inforamtion related to this topic. Thanks in advance.
me too, I need more detailed info.

Good old Bill

When there is a vacuum problem, the system defaults to the defrost position, with you only coming out the floor, leans toward the funtion door broken or stuck in that mode.

The area of vacuum line breakage is under the battery near the vac reservoir.

Worf

x2

jennkent5454

There are 2 reservoir behind the battery, I tested both and both hold a vacuum, I tested the 2 lines and they hold a vacuum, where else or what else should I try? I'm now leaning towards the blender door but how can you test it?

Good old Bill

Its the function or mode door you are after, can't answer the question as I have not had the opportunity to work on one. FYI, the blend door is how they mix the air for more AC or more heat. Have been other posts here about this subject, I know the search button will help out if the right words are used. Let us know how you fixed it, or better yet, put up your procedure in the "How to section".

jennkent5454

ok is thie function/mode door the one that makes the ac or heater blow from panel vents to floor vent to defrost? if so, under the dash to the right of the steering column there is an acctuator, i can opperated that by hand and it will switch to blow out the panel vents when i let go it blows back on the floor and defrost. is this what you are speaking of?

Good old Bill

Yes Sir, thats the puppy. Is that actuator vacuum actuated? If so, with no vacuum, it should go to defrost position (spring loaded). If that seems to be correct and still doesnt function properly when you change positions, perhaps the vacuum switch is at fault.

Good old Bill

Please excuse me for the incorrect input. Just checked my 02 manual air, my mode door is not spring loaded to the defroster mode, it needs vacuum for it to operate. Naturally now I'm doubting my truck as well. I run on max AC, 24/7. I put it to defrost and vacuum was necessary to move the actuator. Guess we need better input from others. But, you still could have a vacuum leak around the battery area where it splits from reservoir to line going thru firewall. Have been alot of confirmed leaks in that area.