The dreaded Defrost only air flow problem.

[xtriggerman]

I'm finally getting around to fixing all the small issues on this 97 and this one needs seasoned in put. I have the shop manual with the extensive trouble shooting procedures but there is an issue the manual does not address. Every thing works and lights up as it should aside from the air flow is in the default as in defroster vent only no mater what you push. I can't get the EATC to go into self test! I tried a dozen times.... push OFF and FLOOR together and in 2 seconds push Automatic. Nothing happens in the window aside from what ever was going on before the 2 button push. When I start the car, it looks like all the LED characters light up in that split second but no way can I initiate the self test to see if there are any DTC's. I had read some where that these things can go into default simply because of a battery disconnect and you can restore the air flow registers by simply clearing any DTC codes. Is this a indication that the module is shot? Any ideas? This car only has 69K miles on it.

 

[germansheperd]

Heater blend door actuator.
The Pros: fairly inexpensive part.
The Cons: a ROYAL PAIN IN THE A$$ to do.

 

[xtriggerman]

The blend door is working fine. I have plenty of heat and cold AC in the air flow. I already fixed that. But thanks for your response.

 

[Scallywag]

Have you checked the vacuum hose that runs along the top of the engine to the passenger side and through the firewall?

Lincoln Mark VIII defrost only air - Google Search

Even though you already fixed the blend door issue(replaced?), I figured I'd quote this post and bold a secondary function besides allowing heat to pass through.

dude the blend door is either broken again or the grey arm that the blend door linkage goes to is broken. there are 2 arms that move with the blend door, one is actually on the blend door motor, the other is lower and right behind the glovebox door, i bet one of them is broken, if they dont move together, it wont work right, one of the arms moves the door to ac or heat, the other door is a diverter door for the different areas of duct work for the air to go to , vents, floor, defrost ect.....

A/C not blowing out of vents

But more than likely it'll be the vacuum hose.

 

[xtriggerman]

Thanks Sw. I looked the black line over at first and it was in tact. The google link had some good info in it. Namely bypassing the Vac Reservior at the 3 port check valve. Im sure I'll find it eventually but every tip like that can be a time saver. It still bugs me that the Ford shop manual's first move is do the self test and then the vac testing. I guess that's another question. Does the EATC need black line vac in put to initiate the self test procedure? I'm going to find out one way or another when I get more time to play with this issue.

 

[Scallywag]

That I'm aware of, the EATC does not need the black vacuum line to run the self-test as it is an electronic command performed on the control module.

However, since I haven't had the need to mess with the HVAC in either of my Marks for such a long time, I forgot whether the codes from the self-test can indicate a loss of vacuum or if it's merely electrical testing. And of course, now that I'm curious to see what the codes indicate, I can no longer find the section for the DTCs in the CD manual where I thought they'd be(Climate Control System — Diagnose & Troubleshoot)...

Also, to clarify the self-test, AUTOMATIC has to be pressed within 2 seconds as opposed to in 2 seconds. The difference being that if you're counting 2 secs before pressing Automatic, then you could possibly be pressing a bit too late and the EATC ignores/cancels the test rather than if you press it immediately after pressing the OFF/FLOOR combo.

 

[xtriggerman]

Yes, it is with in 2 seconds. Trust me, I'v tried it in every conceivable combination of push, let up push hold and push, before & at 2 seconds..... every thing and it simply ignores what should be a very simple input. Clearly, something is bad inside the module. I have a used one coming in the mail just in case the Vac pans out OK. This week the car gets a Dynotech drive shaft and sending unit/fuel pump. The darn fuel gauge takes about 50 miles of driving before the needle on the gauge gets up to where you just filled up with gas earlier. Getting rid of the bugs that bug me is just going to take a little time and help from the fans here.

 

[xtriggerman]

End of the road on this problem. The EATC control was bad. I bought a used one off Ebay for 55 bucks and with fingers crossed, it all works perfectly now except for the self test! This new used unit will not respond to self test either. I would mention tho that the vacuum reservoir's purpose is to keep the dash/floor vent air flow from migrating to the defrost vent under WOT acceleration. I have read a number of folks have asked about that issue.