Diagnosing a HVAC vacuum issue on a Ford F53
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...
Forum Discussion
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!
