F-250 a/c vent issue??

[zztex]

a/c went from blowing out the proper vent to blowing out the defrost vents? This happened within 10 seconds of turning the 4x4 switch on. Any ideas? Thanks

[Smart]

You have a vacuum leak zztex. Blowing out the defrost vents is a tell tale sign. The vent doors are controlled by the vacuum.

I would check your hoses for leaks starting at the hubs on the front if you have a 4x4.. They tend to crack right where they go into the hub. The hose is cheap and easy to get to if you take off the tire. It basically just slips over the teet on the hub. Also check all the other black hose in your vacuum system. I just did the same for my ESOF 4x4 which is controlled by the same vacuum system.

Second, make sure you vacuum pump motor is working. It will be on the passenger side wall of the engine area right above the passenger tire. It sounds like a plug in air compressor when it is working.

Third will be your vacuum air storage box which is right next to your vacuum pump. In my readings, these leaking are rare but it does happen.

[kfd82]

You have a vacuum leak zztex. Blowing out the defrost vents is a tell tale sign. The vent doors are controlled by the vacuum.

I would check your hoses for leaks starting at the hubs on the front if you have a 4x4.. They tend to crack right where they go into the hub. The hose is cheap and easy to get to if you take off the tire. It basically just slips over the teet on the hub. Also check all the other black hose in your vacuum system. I just did the same for my ESOF 4x4 which is controlled by the same vacuum system.

Second, make sure you vacuum pump motor is working. It will be on the passenger side wall of the engine area right above the passenger tire. It sounds like a plug in air compressor when it is working.

Third will be your vacuum air storage box which is right next to your vacuum pump. In my readings, these leaking are rare but it does happen.

Spot on.
Had the same issue with my 99 F-350.

[Rudey]

Yep. Vacuum problem. If you really need the 4x4, manually lock the hubs instead of using the switch. But fix the leak and you'll have best of both worlds.

[zztex]

From my research, it appears to be the ESOF valve. This sound right to y'all?

[Shiner]

since this happened when you engaged your 4x4, most likely its the hubs leaking. You can take off hoses at your wheel hubs and plug them. then see if your vents come back. You can still lock in hubs manually and have 4x4 until you can repair it properly

[bowpete]

Vacuum pump issue, eaasy fix.

[zztex]

since this happened when you engaged your 4x4, most likely its the hubs leaking. You can take off hoses at your wheel hubs and plug them. then see if your vents come back. You can still lock in hubs manually and have 4x4 until you can repair it properly

Thanks, I tried that and still had issue. Vacuum pump runs constantly with key on which tells me there is a leak. Trying to determine next step. Had a new stereo installed a couple of months ago. First time in 4x4 since then. Also had vehicle detailed before the weekend, mats pulled out, etc. Looking for something knocked loose? Not sure about pulling my dash loose

[Palmetto]

Plug it off at the Vaccum Pump. That will eliminate all the hose from the pump to hubs.

[BigL]

as others said vacuum leak. I had a small pin hole in a vacuum hose and it would do the same thing.

[ltljohn]

ALSO note (experience is a cruel teacher ) that 4 wheel drive will not engage automatically when you have a vacuum leak. It will still work if you manually lock in the hubs though.

ltljohn

[Gator]

Look for a small loose hose on top if the block passenger side, same thing happened to me and that was it

i quit culling when i found out i was a cull..sent via tapatalk

[BigL]

ALSO note (experience is a cruel teacher ) that 4 wheel drive will not engage automatically when you have a vacuum leak. It will still work if you manually lock in the hubs though.

ltljohn

that is true. I found out when I got stuck in mud because of it. It's what caused me to take the truck to the mechanic. That was a wet year when it happened. I was at like 75k miles now I have 225k miles if it tells you how long ago that was...

[zztex]

Been troubleshooting today. What I know is it's not the hubs and not the vacuum pump. Will continue tomorrow

[Iolabowhunter]

ZZTEX,
Look on top of motor, next to firewall on passengers side. Round Module with vaccum hose. Same thing happened to me after oil change. F350