My heater is stuck on the defrost mode. I checked the vacum lines, they are fine. I have a 3 prong sylinoid with two vacum line conectors which I replaced with a new one that is located next to the battery on the firewall. I have read it was supposed to engage to create vacume when I switched from different settings like floor to defrost. I never hear the sylinoid work. This same sylinoid is also supposed to engage my ESOF. The ESOF does not matter cause I have switched to manuel hubs. Any thoughts from the experts or ones gone down this same road.
I'm far from an expert, but from what I've read here trying to get my ride up to snuff (99 F250 SD 6.8L CC XLT 4x4) it does sound like there's a vacuum leak. When you said you checked the lines, did that include the ones for the ESOF you don't use anymore? If they were removed when you changed to manual hubs, could any plugs/new lines have come loose?
Like I said, I'm not an expert, just trying to help.
I s there vaccumn available at the soliniod or climate controls? What engine do you have? Depending on the year the diesels have an electric vaccum pump on the right fender underhood that fails occasionally.
Random question but, does ur overdrive switch still work? I had a 96 tbird that i bumped my od button and the defrost would only turn on. Turned out to be a bad fuse... my fuse was the ACC fuse. Just a thought.
Guys...not sure this is vacuum related. My 2003 has been switched to manual hubs, and the vacuum lines are not plugged, and my heat/ac controls all work fine. My father in law's 99 has ESOF with NO lines or plugs, and his heat/ac controls all work fine. If I recall, the defrost/floor/dash door is actually electrically controlled and there is an electric servomotor on the heater box under the dash that controls it. I know for sure that is how the temperature is controlled, because I had to replace it on my old 99. So you may want to look into that.
I checked my vacum lines, they are fine. The vacume for this truck is held in a canister behind the battery passenger side. I believe the vacume is created with a sylinoid on the firewall next to the battery. I also believe this same sylinoid engages the auto hubs for the ESOF. It is a new sylinoid and does not make a peep. The sylinoid on the transfer case that engages the 4x4 is an aftermarket. Would that have anything to do with the sylinoid on the firewall not responding.
Repaired a Jeep Wrangler for a friend one time.
Battery acid had dissolved the 4x4 vacuum hub
hard line tubing. Put in a couple thick walled rubber
tubing splices, the dealer wanted over $300 to
fix it, I did it for free.