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

22 Replies

Gdetrailer
Explorer III
Dec 01, 2018
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..
Mike_Schriber
Explorer
Dec 01, 2018
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

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Diagnosing a HVAC vacuum issue on a Ford F53

22 Replies

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