I had the strangest thing happen yesterday - we were returning from a weekend camping trip and had been driving for about 1.5 hours witht he A/C (front and rear) running full blast in the 92 degree heat. We had stpped to pick a bite to eat and I sat with the X running while the wife went in a grab some burgers. We pulled away and about 10 minutes later (driving at about 35 mph), the A/C switched from the panel to blowing only through the defroster. It stayed like that for a few minutes, then switched back. It did this few more times later in our trip at different speeds with no real rhyme or reason to it.

My first assumption is a vaccum leak/failure, but I don't know where to begin.

Any thoughts? Has experienced this?

 

Might not be much help.... but I had the same thing take place
in a Ford conversion van recently. It switched during moderate
to extreme pull on the engine. As in going uphill or accelerating
heavy. Turned out to be some type of switch in the dashboard
that had to be replaced.

 

MarkMoore .... There was a thread on this issue either in the Ex forum or the Superduty one. A couple guys referenced to vacuum issue with the 4X4 selector on the axle I think? Seemed to be a common issue with the 4x4 guys.

 

Interesting. I just had the same problem on our '03 4x4 PSD.

We are enroute to San Diego and it is pretty hot in New Mexico. Ford dealer in Santa Fe was booked when we got here, so they could not help.

By studying this issue here on the forum, I was able to isolate my problem to what I believe to be the 4x4 vacuum switch(?). This unknown switch is right in front of the vacuum motor on the passenger side wheel well arch. By plugging the lines going into / out of this switch, I stopped the system from blowing through defrost vents. We lost Auto 4x4, but small price to pay for cool air in our faces. Everything else appears to work OK.

Tomorrow, we drive on west, towing out big travel trailer. Hopefully, I have found the root cause (external leak in this vacuum switch?), and we can travel in comfort.

By the way, the first thing I noticed was this weekend when the 4x4 would not switch automatically.

Another clue: With hood up, turn on the key without starting engine. The vacuum pump should run but stop within about 60 seconds once vacuum is established. If you have a major leak (like mine), it will run continuously.

 

Just a note to let few visitors know about my vacuum fix--it worked. We had A/C for our >3000 mile trip to San Diego and back via Las Vegas. Good thing, too as the temperature was 122F in Laughlin, NV.

This week I hope to find the real source of problem (vacuum switch? Hubs?).