On a 2002 F150 the A/C will only blow out the defroster, sometimes it will kick back to the vents but then it goes right back. Is this electric controlled or vacuum?

 

the selector for defrost, vents or floor (the ****) is vacuum controlled. two vacuum cylinders pull doors to direct the air up or down to these vents. the vacuum line starts in the engine compartmet right side, rear of the motor. it is a small black line about 3/16 diameter. has a TEE at the firewall about where the glove box is. Goes thru a rubber gromet at that point. Normally the TEE has a bad rubber fitting on it. the TEE also goes to an accumulator tank between the battery and the fender. Look for the TEE and inspect it. Pull the TEE apart and check that you have vacuum at that point. If so, you might have a leak on the backside of the control ****.--- the default position is to defrost (no vacuum) so you can defrost the windows if it fails.

 

My vents are also stuck on Defrost. There's a group of vaccume hoses (color codes) that run to a connector just to the upper-right of the throttle. I think that's where my leak is (I accidentally pulled the lines out of the housing when trying to disconnect it when I was replacing my heater core).

 

Thanks for the info. I'll look at it today.

 

Same exact thing happened to my 98. It turned out to be a vacum hose behind the battery..It was pinched off.

 

Mine ended up needing the whole A/C Control Unit replaced. Over $400 for part at local dealer.

 

OUCH!!

 

The accumulator tank (vacuum reservoir) on Econoline vans leaks eventually for almost everyone. Check yours (it's impossible to change in vans). This tank stores vacuum for periods when the engine is under high load. The system defaults to defrost when vacuum is low.

 

On a F series
By 2002 most do not have a vacuum mode switch or any vacuum controls whatsoever for the HVAC
His 2002 should have a mode door actuator on top of the hump below the HVAC case
Most common is broken gears and then being stuck on defrost or wherever it was when the gear broke

 

You older -timers should know better when a relative noob uselessly necros a thread from almost 20 years ago.

The original thread was about the F150, not a van.

Ford switched to electronic mode door actuators beginning with the 2004 NBS F150. Anything 2003 (including '04 Heritage) and older still used vacuum motors.

 

I apologize for mentioning a van, but I assumed the failure mode would be similar on a truck. I thought this item was applicable.

 

I think of the plenum case design and sometimes forget what model line has what
IIRR
By 97 no Expedition or Explorer ran vacuum to the HVAC case They, Taurus, Mustang and Crown Vic all used the same case

 

It makes me wonder if one could spray, paint, dip something on the outer surface of that little tank to seal it, or would one just have to buy another vacuum tank?

 

That sounds like a possibility to seal that tank, but on my ‘03, what went sideways is the vacuum line that tees off the vacuum tree and darts right into the firewall. That hose was all chewed up. Heat must have broken it down over time.

You can smoke test the setup just to make sure the issue doesn’t go farther than that, which I am confident of in my case after doing some looking with an inspection scope. One of these days, I’ll pull the battery and tray and try to stab a hose back in there before it gets too toasty outside.