Dash A/C blows out of defrost when climbing or head wind

[kmb1966]

My dash a/c blows cold air, but at times when climbing hills/overpasses or traveling in a head wind, the air will decrease out of the vents, and blow out of the defrost vents. Upon slowing down, the air will return to the front vents. I've brought it to nearly every shop in town, with most scratching their heads after replacing lines and check valves and saying 'just live with it'. No. I don't want to live with it. I want it to blow out of the front vents. I've heard (on this forum) that a secondary vacuum pump could be added to solve this problem. My question is WHERE do I find this pump, and WHERE would it be installed? I'm clueless on where I would put this auxiliary pump for additional vacuum. :h
2000 Ford F53 Chassis

[dougrainer]

FIRE UP wrote:

bakedalaskan1 wrote:
Ford has a technical service bulletin that addresses this. It fixed this situation in my 2001 Winnebago. I replaces the vacuum reservoir with a larger unit. TSB 02-07-02 AC COMING OUT DEFROST.pdf

Hmmmmm, imagine that, a fix WITHOUT the addition of an auxiliary vacuum pump. I surely understand that Diesels do not produce vacuum therefore, there is a need for a vacuum pump. But, gas engines DO produce vacuum and, have stored it in one or more storage vessels forever. To me, this situation would similar to a diesel coach with a fair sized air leak. And folks would just add an auxiliary air compressor to augment the engine driven one, to keep up with the air leak, rather than fix the leak. Same thing, only pressure instead of vacuum.

Now, maybe the OP has taken his coach to various techs and, so far no luck in finding the culprit but, the fact remains, there's a leak SOMEWHERE and, all those techs just haven't found it. Seen this kind of thing many times where multiple attempts to repair an issue
failed and then, someone comes along and jumps right to the problem.
Scott

Interesting. FORD put out a TSB for a problem that had NOTHING to do with a FORD part or install. Sorry, this problem will NOT be fixed by a larger Reservoir. I have installed dual Reservoirs 20 years ago to attempt to fix the problem. It just Delay's the time it takes for the problem to happen. The ONLY sure fix is the 12 volt pump. Doug

[Sastma]

This is very timely. Great posts!!
We are having the same problem with our 2010 F53, but I can’t seem to find the TSB. I’m just reading this this evening so not looked under the hood yet. Just doing my typical online research. That said, can I order the replacement canister online? Where?
Looking forward to getting this resolved as well.
Thanks!

[mowermech]

keefr wrote:
Anyone remember the old vacuum-operated windshield wipers that stopped going uphill and flapped like crazy coming down?

Yes, and I also remember the "fix" that was done back then: The double diaphragm fuel pump. One diaphragm to pump fuel, and one to create vacuum for the wipers. It didn't completely solve the problem, but it helped.

[kmb1966]

dougrainer wrote:
The Pumps ALL make the noise, even Diesel motorhomes. It IS that inherent vacumm leak present in the system that causes the motor to cycle. You can insulate the mount with rubber or foam to minimize the noise. Doug

yes. Will do that next. I mounted directly onto the metal. some rubber washers may help. So glad to have it working again. I have had this problem since it was new, and have had so many techs look at it, try to fix it, with little to no improvement. Thanks again!

[dougrainer]

delete

[dougrainer]

The Pumps ALL make the noise, even Diesel motorhomes. It IS that inherent vacumm leak present in the system that causes the motor to cycle. You can insulate the mount with rubber or foam to minimize the noise. Doug

[kmb1966]

UPDATE: 09/02/2018:
I am the original poster. I ordered the new vacuum reservoir and harness as indicated in the Ford Technical service bulletin (as suggested in this thread). But I also went forward with installing the 12volt vacuum pump (also as suggested in this thread). I connected the 12 volt pump to the fusebox (protected it with a 3 amp fuse) and connected it up to the existing vacuum reservoir, plugged the vacuum hose that originally was connected from engine.
I put a dash switch on the vacuum pump so that I can turn it off in the event I want to.
Tested in a 150 mile trip so far:
A/C vents blow correctly and much better than ever. So far, it has not blown thru the defrost vents unless it is in defrost mode.
The only drawback that I have seen so far is that the pump is NOISY. I can hear it come on and off at times. I can deal with that as long as the a/c blows correctly. We use the dash a/c and at times has saved us because the Onan was being problematic and could not run the main a/c system. Besides sometimes in the hot weather, it feels good to have the dash a/c blowing nicely up front for relief.
Will report more on this as I continue to test, but so far what Mr.Doug suggested works perfectly (although a little bit noisy).

[MrWizard]

Yes and no
Manual valves on vacuum actuator seals well, vacuum motors leak

[FIRE_UP]

bakedalaskan1 wrote:
Ford has a technical service bulletin that addresses this. It fixed this situation in my 2001 Winnebago. I replaces the vacuum reservoir with a larger unit. TSB 02-07-02 AC COMING OUT DEFROST.pdf

Hmmmmm, imagine that, a fix WITHOUT the addition of an auxiliary vacuum pump. I surely understand that Diesels do not produce vacuum therefore, there is a need for a vacuum pump. But, gas engines DO produce vacuum and, have stored it in one or more storage vessels forever. To me, this situation would similar to a diesel coach with a fair sized air leak. And folks would just add an auxiliary air compressor to augment the engine driven one, to keep up with the air leak, rather than fix the leak. Same thing, only pressure instead of vacuum.

Now, maybe the OP has taken his coach to various techs and, so far no luck in finding the culprit but, the fact remains, there's a leak SOMEWHERE and, all those techs just haven't found it. Seen this kind of thing many times where multiple attempts to repair an issue
failed and then, someone comes along and jumps right to the problem.
Scott

[Dutch_12078]

keefr wrote:
Anyone remember the old vacuum-operated windshield wipers that stopped going uphill and flapped like crazy coming down?

Yep... We used to make our own vacuum reservoirs from large juice cans. Back when the cans were actually made from tin that we could solder homemade fittings to. That made a big difference unless it was a really long uphill climb.

[BigRabbitMan]

keefr wrote:
Anyone remember the old vacuum-operated windshield wipers that stopped going uphill and flapped like crazy coming down?

Yes, I could play with the wiper speed with the throttle! On long uphill grades you had to momentarily lift the throttle to get a quick wipe of the windshield.

[keefr]

Anyone remember the old vacuum-operated windshield wipers that stopped going uphill and flapped like crazy coming down?

[MrWizard]

according to my ford chassis manual revised 1994 version

class A MH fuse box

fuse number 8, 15 amp. run only, for body builder add-on circuit

i have no idea what your builder used that circuit for or IF it is the correct fuse for your 2000 chassis, but load should be minimal and able to handle the extra vacuum pump
it is a place to start looking/testing

[Dutch_12078]

Adding a second reservoir helped with the low vacuum problem on my coach, but mostly just delayed the inevitable on long, hard pulls. As Doug said, adding the pump was the real fix. My pump came from a wrecked F-350 diesel pickup.