EATC acting funny, no trouble codes

[Grand Marquis GT]

So, my EATC doesn't do the right thing. I have on Auto, A/C or whatever it will blow nice and cold out the vents for a moment or two then switch full blast to the defrost vents. If I pop it on vent, it won't always switch back.

I get no trouble codes (888). What gives?

[FordMan77]

Does the switch to the defrost vents occur along with acceleration?

[86VickyLX]

You most likely have a vacuum problem. They still use vacuum doors on the positions iirc.

[FordMan77]

That's what I'm getting at. My 03 Sport had this issue and I had to mod the EATC unit to fix the issue. Either that or get a new one from Ford for $500, which will probably have the same issue again. I also showed no codes in the EATC module.

The issue with mine is that one of the vacuum heads in the unit was not sealing, so when engine vac. dropped (accel), the EATC would loose vac and go to defrost setting, which is the default setting in the event of a failure.

I took mine apart and used an explorer EATC just for the vac. guts, added 2 wires to match the old unit and away she went. No issues so far and I did that last year. I can get details if needed.

[Grand Marquis GT]

UPDATE!

I did the o-ring fix to the stock EATC, to no avail. So, I got a used one from a '00 GMQ. Works like a champ.

Then, my I see my dog is chewing on something. It's one of the plungers from the EATC that I rebuilt. No wonder it didn't work