I've posted this in the HVAC section, but haven't gotten a whole lotta help. Anywho, my 2000 F-250 PSD is stuck on defrost. A/C works when you turn the selector to it, but still on defrost. Off = fan off, but you can still feel some air coming through the vents. Everybody keeps saying its a vacuum leak, however, my auto hubs STILL lock. Any ideas? I found this connector today on the driver's side floorboard, and its unconnected. Didn't see where it went either.

 

I know my parents had the same issue on their 2000 PSD and the small air compressor under the hood that builds up the vacuum for the diesel was gone. If you turn on all the vents and rotate the selector **** back and forth with the engine off you will empty the reserve. After have some one turn the key on but dont start the engine while you go out under the hood by the passengers fender and see if you hear the pump humming. Ours would work if you tapped on it with a screwdriver but would stop again. I know the part is like $135 and is an easy install. The easiest way to replace it is to remove the compressor and the base it is on. Then remove it from the base and mount the new one by pushing the 3 rubber mounts into the holes in the mounting plate. Hope this helps.

 

Where is this compressor? Any pics of it? I've tried looking but can't find anything, and NONE of the local parts stores have a service manual... I ordered one off ebay, and it should be here this week....

 

If I remember correctly it is between the a/c compressor and condensor and the battery on the passengers side...it is about the size of your fist and has a wire coming to it and a small air line. I will see if I can find a picture.

 

I think this picture will help you. The green circle is where the pump is.



Also sometimes when the pump goes it will blow the fuse it is run by so if you replace the pump and it still dont work check the fuse. I know if you turn the key on you will hear it run to pump up the vacuum...It is ford part #6C3Z2A451A....hope this helps

 

Also there is a TSB out for this issue that may help...

here is a link:

http://www.ford-trucks.com/tsb/fullt...hp?tsb=05-17-4

 

AWESOME! That is exactly what I needed..thanks a ton!

 

Update... replaced the vacuum pump today, and that DIDN'T fix the problem... Any other ideas?

 

Before you replaced the pump did you see if it worked?? Also did you check the fuse for it? Other than this I dont know what it could be unless that harness goes to something to run the vent doors.

 

I got to thinking today... could it be my selector switch? It does select A/C, but not MAX A/C. Is there any way to test it? And the vacuum pump is operating normally. 4x4 auto hubs are working too...

 

Finally got around to getting a vacuum pump tester from Advance Auto. Turns out my check valve mounted on the passenger side fender was broken.... My front hubs were engaged the whole time. Guess thats why I could only get 15 MPG if I was easy on it. Got a new valve, and everything works great. Truck feels much quicker now too without the front axle engaged.

 

I've been having the exact same problem with my f250. The A/C will operate through the defrost vent, and will periodically switch back and forth. Can you post a pic of the check valve, and how much did it cost you? Thanks

 

The valve was like $20. No pics yet. Go follow your vacuum lines, there's only 2 if you have 4x4. 1 if you don't. Its mounted right by the vacuum reservoir.

 

I think I've gotten this thing fixed and believe it was just a sticky valve or something inside the pump. I pulled the outlet hose, put my finger over the outlet, and held it there until the pump shut off. It ran for about 30 seconds before it finally did shut down, but once it did, I replaced the outlet hose and it has been running normally ever since. I don't know if that was a permanent fix or if the pump will go haywire again soon, but I've been driving it for 2 days now and haven't had another problem with the intermittent switching from vents to defrost. You guys might want to try this before buying a new pump.