2010 E350 wagon: when going up hill or under acceleration, both my front and rear blower fans cut out. It doesn't matter if the controls are set to AC or vent. When the road levels out or the RPMs drop, both fans come back on. Since both fans are cutting in and out, I am not suspecting electrical, rather vacuum since each fan has its own relay and circuit. I do not see anything wrong (visual only) in the vacuum lines under the dash or under the hood, but then again it was only a visual.

 

I was able to resolve this issue. The vacuum reservoir was leaking. The original is in a totally inaccessible location under the blower fan. I went to my local salvage yard and got a “soup can” style reservoir out of an older Lincoln and mounted it in the engine compartment. I then ran the original vacuum line off the engine to a vacuum valve. From here, one line to the newly installed reservoir and one down through the passenger foot area (original vacuum hole) and attached to original lines. Works like a champ.

 

Thanks for the update..

Necessity is the mother of invention!