I have both a 99 F-250 SD and a 01 F-350 SD both with ESOF, both 7.3 PSD.
The 99 will not do a ESOF but works when hubs are put in LOCK.
So I did a search of this forum and started to track the vacuum system for leaks or failed parts. In fact the vacuum pump never stops pumping and the defrost is always on. All indicators of a failed vacuum system per posts on FTE.
No leaks found, vacuum pump working, checked vacuum at each connector starting at pump. There is NO vacuum at anytime from the output port of the hublock vacuum actuator located on the "shot gun" (right) side of the truck. If I plug the RED input line to actuator the vacuum pump will shut off and heating system works correctly. If I plugged the output port of the actuator the vacuum pump never shuts off, on matter what possition 4WD switch is in, heating system is on deforst only.
Switched out actuators from 01 to 99. Retested items listed above. Every one of them tested OK! Plus the heat system is working correctly. The 99 installed in the 01 failed the same tests as I used on when it was in the 99 and the heating system fails in the 01 with 99 actuator installed.
So it looks like it is this actuator has failed.
Does anyone know the correct Ford part number this darn thing! I have look all over the internet and can not find it. I could go to my local Ford dealer and pay his retail price, but I am a little Scotch and would like to see if I can buy it for less from one of the online Ford parts places. I think it is a Ford ONLY part.