Hi, hoping someone can help me out here. Its hot in St. Louis and my windshield sure is staying cold (ac blows from defrost vents only).

1999 Ford F350 7.3 diesel 4x4 (4x4 lever on the floor). About a month ago, the ac starts blowing out of the defrost vents only. I assumed it was a vacuum issue.

Lines looked good; very plyable still. Canister looked fine. The vacuum pump on the pass fender well smelled burnt, so I replaced it. Got the new pump in and it didn't work. Checked the fuse panel and found two blown fuses, replaced them and the pump worked.

Here's my issues: if AC max is used, the vacuum pump stops working and air blows through defrost only . If the dash switch is in the off position and then turned back on, air blows through defrost vents again and vacuum pump will not work.

Is there a solenoid or switch to this vacuum pump that I'm not seeing? Thanks for your help, Dave

 

Had the same problem about a week ago. Mine was just a fuse. But there is a vacum actuator below the glove box on the firewall. Just a guess.

 

sometimes in 4x4 systems when you turn the switch it will go to defrost indicating a vacumn leak usually at the hubs.

Kind of don't think this applies in your case but worth a look.

 

Thanks guys. I'll need to take a closer look. I see a vacuum line leading down, but haven't seen a vacuum line near the hubs.

I keep reading different forums about this same issue, but it seems to only apply to trucks with the 4x4 switch on the dash, unlike my lever operated one.

Also wondering if the new vacuum pump is defective. When the pump stops working a little tap on the housing will turn it back on and then air blows from the vents...

 

If you have a manual 4x4 then that is not your issue.

 

Senix, thats sort of what I was thinking. So, manual 4x4 means, no vacuum?

 

No vacuum. Just the lever on the floor.

 

The only way to go. IMHO.

 

Firefighter, thanks for letting me know about the actuater behind the glove box. That was the cause of my problems. There is a white vacuum line leading to that and a passenger must have kicked it off.

Plugged it back in and its been good so far (two days); all back to normal. Thanks again guys-Dave

 

Sweet deal. Glad you got it fixed.

 

Great outcome