The AC/heat is switching to the defroster under higher RPM conditions on my 2006 F53 chassis Damon. It actually seems to be doing it now under low throttle steady state conditions as well. Obviously a vacuum issue but I'm not finding any obvious leaks.The leads me to focus on the vacuum accumulator but I'm not sure how to test it. I can't even figure out how to remove the lines going in and out and I don't want to break anything fumbling around. Any suggestions?Thanks!Mike

Actually... I just unplugged the hose from the accumulator where it connects to the dash controls. The baffle for the defroster immediately dropped and the line was hissing. The engine has been off for a half hour so that tells me the accumulator is fine. It would also suggest there's no leak elsewhere in the system which makes no sense.Any thoughts? It could be between the manifold and the accumulator but as near as I can tell that line is fine. The other vacuum line from the manifold goes to a device with an electrical connector on the driver's side valve cover. I'm guessing this is a valve related to the PCV system and if it was bad I guess it could deprive the whole system of vacuum but I don't want to go down that road without more information.Thanks (again)!Mike

Sounds a lot like a chaffed or cracked vacuum hose, may not hear the leak depending on the location of the leak.Most likely will need to start inspecting all of the vacuum hoses, not sure what engine you have but there are a few well known issues with vacuum lines and hoses on the modular engines which have a history of chaffing and or cracking from heat in the engine bay..

Take a small propane torch and unscrew the head leaving just the valve and pipe, then slip a piece of tubing over the end of the pipe. With the engine idling and the valve on the torch open (but not lit obviously) run the end of tube along every vacuum tube in the HVC system. When you get to the vacuum leak the engine will inhale the propane and the extra ‘fuel’ will cause the engine to speed up a little, when you pull it away it goes back down again. It makes finding vacuum leaks super easy.

I have heard of adding a vacuum pump to run the dash.

This is a common problem on Ford Class A chassis going back over 20 years. The ONLY sure fix is to install a 12 volt vacuum pump and plug the vacuum line from the engine. You will have people tell you to test this and test that and add another accumulator, and check all the vacuum lines and motors on the dash evap system. The plain fact is, the aftermarket Dash AC systems on Ford Class A's have inherent vacuum leaks and cannot overcome the engine going to zero vacuum on full acceleration or climbing hills. You can do a search for this problem on this forum and see all the silly things people are told to do, when the plain fact is, you need the 12 volt pump. I speak from over 38 years and still working on Motorhome Dash systems and YES, I have installed a few of the 12 volt pumps, even years ago when the Coach Maker paid for the pump installation when the RV's were under warranty. Doughttps://www.amazon.com/APDTY-015325-Vacuum-Pump-Supplemental/dp/B00BVQZSKO

Diagnosing a HVAC vacuum issue on a Ford F53 | Good Sam Community

pwn
Explorer
May 30, 2021
Well, I'd like to thank JimDandyAZ for his post. It has helped me tremendously with a problem that has been plaguing me for almost two years. THANKS FOR reviving this thread and reposting this information.
Gdetrailer
Explorer III
Sep 02, 2019
Jeeze JimDandy, nothing like reviving a LONG DEAD thread, OP found their problem and fixed it RIGHT nearly one year ago.. AND it didn't require a bunch of hokey aftermarket parts..
JimDandyAZ
Explorer
Sep 02, 2019
APDTY 015325 Vacuum Pump -... https://www.amazon.com/dp/B00BVQZSKO?ref=ppx_pop_mob_ap_share

APDTY 112687 Wiring Wire Harness... https://www.amazon.com/dp/B00UG9VZDG?ref=ppx_pop_mob_ap_share

E Support 12V 24V Standard Add A... https://www.amazon.com/dp/B0146EB8EM?ref=ppx_pop_mob_ap_share

https://www.dormanproducts.com/c-98-vacuum-

Hose from local auto store

Parts
JimDandyAZ
Explorer
Sep 02, 2019
dougrainer wrote:
This is a common problem on Ford Class A chassis going back over 20 years. The ONLY sure fix is to install a 12 volt vacuum pump and plug the vacuum line from the engine. You will have people tell you to test this and test that and add another accumulator, and check all the vacuum lines and motors on the dash evap system. The plain fact is, the aftermarket Dash AC systems on Ford Class A's have inherent vacuum leaks and cannot overcome the engine going to zero vacuum on full acceleration or climbing hills. You can do a search for this problem on this forum and see all the silly things people are told to do, when the plain fact is, you need the 12 volt pump. I speak from over 38 years and still working on Motorhome Dash systems and YES, I have installed a few of the 12 volt pumps, even years ago when the Coach Maker paid for the pump installation when the RV's were under warranty. Doug

The truth was in the middle. I found a vac leak with a pump tester. And Doug Rainer was right .. the F53 dash is inherently leaky. Installed the vacuum pump Doug cites. Bought the wiring harness while only using the black and green. Tied power to an ignition- on piggyback fuse. Unit shuts off when vacuum is correct. Does not run when ignition is off due to choice of where to tap 15 amp fuse.

***Link Removed***
kmb1966
Explorer
Dec 04, 2018
dougrainer wrote:
This is a common problem on Ford Class A chassis going back over 20 years. The ONLY sure fix is to install a 12 volt vacuum pump and plug the vacuum line from the engine. You will have people tell you to test this and test that and add another accumulator, and check all the vacuum lines and motors on the dash evap system. The plain fact is, the aftermarket Dash AC systems on Ford Class A's have inherent vacuum leaks and cannot overcome the engine going to zero vacuum on full acceleration or climbing hills. You can do a search for this problem on this forum and see all the silly things people are told to do, when the plain fact is, you need the 12 volt pump. I speak from over 38 years and still working on Motorhome Dash systems and YES, I have installed a few of the 12 volt pumps, even years ago when the Coach Maker paid for the pump installation when the RV's were under warranty. Doug

https://www.amazon.com/APDTY-015325-Vacuum-Pump-Supplemental/dp/B00BVQZSKO

I chased this problem down for over 10 years! Went to Ford dealers, a/c mechanics, auto mechanics, so many people looked at this problem and could not fix it for real. Finally, I took Doug's suggestion, installed the pump and problem was fixed for good.
I'd go the aux pump route as suggested. it fixed it and worked without issue after that!
Mike_Schriber
Explorer
Dec 04, 2018
Wow. This got going. My issue is solved. As I posted, there was still vacuum more than a half hour after the engine was turned off so all the other lines are good and so is the accumulator. I've had an issue with this line before. It's not shielded and it's exposed to heat, etc. Looking to replace the entire thing.

I've put 50,000 miles on this rig with plenty of high throttle extended uphill running and I've never run out of vacuum. YMMV.

Mike
JaxDad
Explorer III
Dec 03, 2018
wolfe10 wrote:
Doug's answer IS spot on for any driver of a gasoline powered vehicle who expects adequate vacuum to operate the dash HVAC system under heavy load= low engine vacuum. Suspect a number are fit after a first drive in real mountains where sustained high throttle/low vacuum conditions are encountered.

No question, it will not magically fix other leaks in the system if they are large enough to overcome the supplemental pump.

BTW, that is the standard vacuum pump on a large number of diesel vehicles, since diesel engines have no vacuum. VERY common pump.

And yet those smarty-pants engineers with the coke bottle-bottom glasses and pocket protectors found it entirely adequate to just add a big vacuum accumulator to the system and all is good.....

Unless you have a mechanic who’d rather throw parts at the vehicle instead of actually fixing the problem.......

As a wing-wiper I served with used to say, “maintain it, or you’re in for a looooong walk home.’”
Pirate1
Explorer
Dec 02, 2018
Look for this vacuum reservoir under/near the front right area. They have a tendancy to implode near the plastic welds. It will impact your ac controls.
westend
Explorer
Dec 02, 2018
The leads me to focus on the vacuum accumulator but I'm not sure how to test it. I can't even figure out how to remove the lines going in and out and I don't want to break anything fumbling around. Any suggestions?

As was posted, using an accelerant next to the vacuum hoses is an old school diagnostic technique. I've used ether (starting fluid) for this as I usually have a can of it in the shop.
wolfe10
Explorer
Dec 02, 2018
Doug's answer IS spot on for any driver of a gasoline powered vehicle who expects adequate vacuum to operate the dash HVAC system under heavy load= low engine vacuum. Suspect a number are fit after a first drive in real mountains where sustained high throttle/low vacuum conditions are encountered.

No question, it will not magically fix other leaks in the system if they are large enough to overcome the supplemental pump.

BTW, that is the standard vacuum pump on a large number of diesel vehicles, since diesel engines have no vacuum. VERY common pump.

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