i think i got hit with it!

 

If that's the case then it has to be a leak. Might be a bad storage canister or a hose off.Most common leaks I think are the hoses for the 4X4 hubs.

 

Ok, well what I learned was it could be a vac pump, if I only had one..LOL and that it could be the 4x4 hubs. However to my knowledge, there is no vac at the hubs untill you engage the 4x4. The vacuum then sucks the hub in and locks it in. dis-engage 4x4 and it cuts off the vac supply and the spring mechanism in the hub pushes the hub out of engagement. (I had a lengthy hub issue and I can rebuild em) Also, I have pretty new vac seals for the hubs as I replaced em when I did my ball joints. OYE what a pain that was, and the seals were totalled. Basically they didnt exist and I did not have this problem then, only issue was the 4x4 would not auto engage. I guess, after pouring over the truck last night, looking for a vac leak, and found zero.

UPDATE...Today I learned that my issue is VERY intermitant. Infact it is only when I get on the gass on the highway, and it is even more relevent when towing a load. When its under load and getting up to speed or when gassed it does it. SO it has to be a vac leak but how do you find one when your doing 60 to 80? Cant crawl under da hood then! Taking it to my friends garage tomorrow so he can take a gander, then ill be heading over to another buddies garage for him to take a look at becuase he insists its a vac leak too...but oh where oh where is the air coming from thats killing my vac!

 

Oh and if i disconnect any of the little damn hoses on the R/s of the X under the hood, it just goes right to defrost....

 

I would take the hubs apart , clean, and grease them first. Replace the O-ring in there also, and go from there.

 

Vac is only applied to the hubs when you activate the four wheel drive. thats what sucks the hubs in. If its not activated It should not effect it. However, I plan on doing that tomorrow. all the hoses are tight on the 4x4 checked tonight. no cracks either. ARGHHHHHHHHHHHHHHHHHH

 

Right. Check the entire vacuum system out.

 

Well, from a slightly different view....and I am assuming that the truck does not have automatic HVAC.

I have a 2000 Dodge Viper GTS....which uses the same heater controls as my '05 Ex, & 2003 Mustang Cobra. (Heck, it even has a Ford headlight switch!)

In the GTS, in 6th, cruising at highway speeds...if I merge out to pass, without downshifting...the A/C will start to blow from the defrost vents...then once the throttle comes back to the cruising position...it blows back out the vents. On a Viper...it's considered "normal". One of the Viper guys found that by placing a little check valve in the line leading from the intake rail...it holds position.

Okay...all that being said (seemingly completely off topic)..and not knowing as well how the HVAC works in the Ex compared to the Viper......I'd venture a guess that the actual problem is more like a check valve or an issue where the hoses plug into the HVAC controls, or a leak in the controls themselves? You can hear the hiss as you select different settings.

I'm sure you guys could be right...but here's another option. (and we know what free advice is worth!)

 

I thought of that! Ha great minds think alike? I pulled the dash apart to check the back of the selector switch. I thought it was all electronic actually untill I saw the back of the switch, it was all vac hoses with a slave hose which is black. No hissing. I am leaning to the vac resevoir or what ever its called. Maybe it has a slight leak and when I get on the gas, the vac goes down, and it can not keep up. However I learned fast that If I unhook ANY vac hose Ya damn skippy the AS defaults to the defroster. Im gonna put it on a vac gauge tomorrow, and maybe even try a vac pump to test in different sections of the system. ARgh....

 

Bananrama, please let us know how this works out for you. I have the same issue with a 2001 V10 as we speak...AC going out the defrost vents under throttle load. I just haven't had the time to work on it yet. I have researched it and did find this. https://www.ford-trucks.com/forums/7...lend-door.html Entry 7 by 78crewcabjohn is something I though sounded worth checking into. Hope that helps.

 

ok, well I think I know what its NOT. I by passed the 4x4 vac lines, and had the same issue. NOt the 4x4 apparently. THen, I bypassed the entire vac canister, and everything else and connected the interior cabin vac line right to the vac feed line comin of the intake manifold. Took it for a test drive. happend again. used a vac pump to suck down the vac at the the selector switch while the line was disconected from under the hood and plugged. It held vac. Then cansister, held vac. OYE. I did learn that the RED lines, do not hold vac, because they all T into the intake manifold, dur. Only thing I can think of is that I am not losing vac through a leak. I am failing to maintain vac. when stepping on the gas, you lose vac, common knowledge. I am wondering if there is a check valve that prevents the vac from back flushing (in a way) when you open the throttle gate..... But ill be damned if I can find it. Spent 12 hours today working on this with 3 of my mechanic friends. Tuesday it goes to Tasca Ford, for 91.10 an hour Diag.

 

I've been having the same issue of vents switching to defrost under load and returning when coasting. Note: This is always with the 4wd off.

I checked the vacuum motors under the dash and they all held vacuum from the vac test pump. Then I checked the hoses under the dash for obvious signs of damage or disconnection. I thought it might be the vacuum reservoir, but that tested fine too.

So finally I replaced the "T" that goes from the reservoir to the climate control and ESOF relay with a straight coupler and bypassed vacuum to the ESOF relay. Drove around for a few miles and so far, no problems.

If it continues to work this way, I'll test the ESOF lines & Relay to see what is going on.

Has anyone run into an ESOF relay leaking or sticking open? I keep the hubs manually engaged and just take the mileage hit so I may not worry too much about this for now.

Doug

 

I'm pretty sure the check valve is internal to the reservoir. If you put a vac tester on the accessory side and leave the intake side unplugged, it should hold vacuum. At least that is how other systems I've dealt with worked.

Doug

 

Yeah, mine does not hold vac. Its the resevoir. Its 39.95 direct from ford. However, the mortagage is due, along with both boat payments, SO it can wait untill next week. Ill post the results on here, if it works or not.

 

My hubs are manual, plugged of the auto to them. And my truck still does this exact thing. I don't know if cruise is on the same pump but it works fine. And my mechanic tested my pump and said it was putting out enough, and that I had no leaks. We put it back together and listened for it to shut off. So, undoubtedly, the pump is just bad enough sometimes, to replace, sometimes, I get confused sometimes, and don;t want to spend money on a pump that might not be broke, sometimes.