Join Our Ford Truck Forum Today

Document your Ford truck project here and inspire others! Login/Register to view the site with fewer ads.

Defrost Only AC Operation (Vacumm Leak???)

Beachbumcook

Kansas Chapter member
I need some assistance guys...

1) My AC works fine and blows air out the front vents as normal.

2) When I put my truck into 4WD (ESOF) the hubs lock in (can feel it in the steering wheel) but the AC diverts to the "defrost mode".

3) I can shift out of 4WD but the air still blows out the defroster vents... but if I turn the environmental controls off and then back on... everything works fine and air blows out the front vents again.


I think this is a vacumm leak... but where (based upon the facts above)?

My local Ford dealer just removed and repainted my front bumper and I picked it up today... and now this? Would/could they have knocked something loose (anything is possible)... but how or why???

I am sure they will look at it for nothing... but in the interest of time... where would I tell them to look to save on their time as well as mine?

Thanks,
 

Skandocious

Post Whores Make Me Sick
19,070
651
California
Well your hubs are vacuum actuated, so that would explain why it might be affecting your vac powered vents. Are you sure that both hubs are fully engaging? I'm thinking perhaps there might be a leak in the lines (or possible 1 of the lines got pulled off) in the vac lock hub system. Wild guess-- I don't really know much about those newer rigs.
 

Beachbumcook

Kansas Chapter member
Well your hubs are vacuum actuated, so that would explain why it might be affecting your vac powered vents. Are you sure that both hubs are fully engaging? I'm thinking perhaps there might be a leak in the lines (or possible 1 of the lines got pulled off) in the vac lock hub system. Wild guess-- I don't really know much about those newer rigs.

No idea if both hubs are engaging... just assuming they are?

I guess if one did, then it would still feel the same???

Guess I will find out tomorrow when I go in and have them give it a quick once-over. Darn... and Vince Loney is not on-line tonight to speak with.... of all nights????

Thanks,
 

Skandocious

Post Whores Make Me Sick
19,070
651
California
If you're anxious or you can't get it to the dealer, jack up one tire, lock the hub, turn the tire by hand and watch the axle shaft u-joint through the steering knuckle-- it should spin with the tire at 1:1 ratio if the hub is engaged. Repeat on other side.

Also I would assume you'd have to have the engine running for the vac pump to create vacuum for the hubs-- not sure about that cuz I don't know how that system works.
 

Beachbumcook

Kansas Chapter member
If you're anxious or you can't get it to the dealer, jack up one tire, lock the hub, turn the tire by hand and watch the axle shaft u-joint through the steering knuckle-- it should spin with the tire at 1:1 ratio if the hub is engaged. Repeat on other side.

Also I would assume you'd have to have the engine running for the vac pump to create vacuum for the hubs-- not sure about that cuz I don't know how that system works.

Great...

I have beer but no floor jack.

I have peanuts to munch on but no time this evening.

I have my good looks but no rich women to chase me.

I have 3WD but no 4WD.

Dam... what a night!!!!
 

DNFXDLI

The Token Canadian
Staff member
I just went through something similar with the 750...if there is any sort of low vacuum the heating system defaults to defrost as a protective measure for winter driving....I haven't figured out what's wrong yet...the dealer gave me that info on the vacuum system....so a leak or the vacuum pump faulty.
 

blacksnapon

Moderator
Staff member
Because its diesel, it has to have the vacuum pump for any vacuum at all. The esof hubs get their vacuum source from the hvac (see any pattern developing here?). Making sure the hubs were in fact locking all the way would be a good first step. When you select 4x4, the front driveshaft will turn. Then its up to the lockouts to provide the power to the wheels. It will still fell somewhat like they are locked in even if they're not. The solenoid for the lockouts should be under the passenger side battery. From there its just tracing the vacuum to find a leak. They're right when they say it defaults to defrost when it gets a vacuum leak.
 

Beachbumcook

Kansas Chapter member
Because its diesel, it has to have the vacuum pump for any vacuum at all. The esof hubs get their vacuum source from the hvac (see any pattern developing here?). Making sure the hubs were in fact locking all the way would be a good first step. When you select 4x4, the front driveshaft will turn. Then its up to the lockouts to provide the power to the wheels. It will still fell somewhat like they are locked in even if they're not. The solenoid for the lockouts should be under the passenger side battery. From there its just tracing the vacuum to find a leak. They're right when they say it defaults to defrost when it gets a vacuum leak.

Hey Vince.... do you make house calls?

I know you do not drink... so I'll supply the Coke's and steaks (KC Strips of course).

My local Ford dealer is filled up with truck work and does not have a heavy duty truck lift available... which also means no truck mechanic available.... dam.... it's +80F outside... and I may need my 4WD at a moments notice!!!!

I have a spare room you can even stay in... it will be like a dinner, bed and breakfast weekend for you and the wife.
 

Beachbumcook

Kansas Chapter member
Don't tempt me, Beach! I have to figure out a way to vent the top of my house, or I would.

Wow.... you would put the venting the top of your house ahead of helping me get my 4WD working in July???

Wow... just get the wife to get out the ladder, climp up and cut and install whatever it is you need done.... finished!!! When she is done with that, you guys can come here (with your tools and spare parts of course) and help me fix my truck.

See... it's that simple when you think through the situation!!!!

:beer: :beer: :beer: :beer: :beer:
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
Im gonna take a guess here and say one of your vac hubs might be leaking. I would pull the vac line off one side at a time and plug it, then see if your vents work. If you have both lines pluged and still defrost only the vac pump itself may not be able to pull enough anymore. I'd recomend looking at the lines around the pump and the vac can right next to it to make sure the connections are all good and tight, also make sure your vac line is hooked up to the coolant shut off valve if so equipt and if your truck doesn't have one make sure the that gray vac line is plugged off.
 

Beachbumcook

Kansas Chapter member
Im gonna take a guess here and say one of your vac hubs might be leaking. I would pull the vac line off one side at a time and plug it, then see if your vents work. If you have both lines pluged and still defrost only the vac pump itself may not be able to pull enough anymore. I'd recomend looking at the lines around the pump and the vac can right next to it to make sure the connections are all good and tight, also make sure your vac line is hooked up to the coolant shut off valve if so equipt and if your truck doesn't have one make sure the that gray vac line is plugged off.

All the vacum lines look tight around the pump area... but hey, I am not a mechanic. Where or how do I find or remove the vacum lines on the hubs? What looks like a plastic line (I am not sure what it is for)... or it goes into the universal looking nuckle/joint... is that it?
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
All the vacum lines look tight around the pump area... but hey, I am not a mechanic. Where or how do I find or remove the vacum lines on the hubs? What looks like a plastic line (I am not sure what it is for)... or it goes into the universal looking nuckle/joint... is that it?

There will be a rubber line that goes from the frame to the nuckle, pull it off and plug it with something, see if it makes any difference, then do the other side if one side or the other makes a difference with the defrost then you'll know what hub is leaking. It could also be the solinoid that turns the hubs on and off leaking also, it's kind of hard to do at home I use a smoke machine usually to find the leaks.
 

Beachbumcook

Kansas Chapter member
There will be a rubber line that goes from the frame to the nuckle, pull it off and plug it with something, see if it makes any difference, then do the other side if one side or the other makes a difference with the defrost then you'll know what hub is leaking. It could also be the solinoid that turns the hubs on and off leaking also, it's kind of hard to do at home I use a smoke machine usually to find the leaks.

Thanks.... I'll smoke a cigar while looking at it (ha, ha).

I may attempt to look at it this weekend... or I may just take it to my dealer and have them do it. Spent so much money on another car I have that I hate knowing that my truck is not 100%, but I guess I can live with this issue for a few weeks.

When not in 4WD, my AC works just fine... if it didn't, then I would be at the dealer right away.
 

Beachbumcook

Kansas Chapter member
OK, I think I have narrowed down my problem... so here is a recap so our resident mechanics can confirm if I am doing it right or not?

1) AC works fine and blows out the front vents as normal.

2) When I shift into 4WD, the AC defaults to the "defrost mode" (due to vacumm leak)?

3) When I turn the 4WD knob back to 2WD and shut off the truck or let it go for a few minutes, the AC will return to blowing out the front vents and not defrost.
______________________

Here is what I did to test:

1) I disconnected the vacumm line going from the PVHS (Vacumm Hub Solenoid) to the front hubs at the first 90-degree connection and plugged it with a golf-T.

2) I repeated the same steps above and got the same results!!!

_______________________

My conclusion is this:

1) The problem is with the PVHS (solenoid) and is not related to leaking hubs as the problem repeated itself even with a golf-T in the line going to the hubs?

_________________________

I called my local dealer and they quoted me $73.45 for this PVHS. How does this price sound to you guys? Was my approach to figuring out my problem the proper way to "look at it"?

Please let me know your thoughts....

Thanks,
 

Attachments

  • Vacumm Lines.jpg
    Vacumm Lines.jpg
    46.3 KB · Views: 9

blacksnapon

Moderator
Staff member
That sounds about right, Beach. You've eliminated the hubs as the issue, the only thing left would be the solenoid or the hoses/connections.
 

d-kuzmen

Master Ford Tech
2,109
79
Connecticut
Sounds like your on the right track. If you disconnect the hubs and plug off the line out of the solinoid that feeds the hubs and you get the same results im with you on suspecting the solinoid. As far as the price I don't know i'd have to check, did they give you a part #? I, not working tomorrow but i'll call and check for ya.
 

Beachbumcook

Kansas Chapter member
Sounds like your on the right track. If you disconnect the hubs and plug off the line out of the solinoid that feeds the hubs and you get the same results im with you on suspecting the solinoid. As far as the price I don't know i'd have to check, did they give you a part #? I, not working tomorrow but i'll call and check for ya.

I think it is part # 6C3Z-9H465-BA.

2003 Excursion ltd, 4X4, 6.0L

Please confirm that this is indeed the part I need for my truck referenced above.

Thanks,
 
Top