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BlkRauderMatt
06-07-2012, 04:13 AM
So, under normal or hard acceleration, around 50-65 mph when I have my air conditioner on, it will switch from my a/c blowing in my face to going to the defrost vents..

Nothing on the dash changes when this happens, the air just switches from blowing out the vents to the defrost vents. Not sure why this is happening.. Any thoughts?

Thanks!
Bluerauder
06-07-2012, 04:16 AM
So, under normal or hard acceleration, around 50-65 mph when I have my air conditioner on, it will switch from my a/c blowing in my face to going to the defrost vents..

Nothing on the dash changes when this happens, the air just switches from blowing out the vents to the defrost vents. Not sure why this is happening.. Any thoughts?

Thanks!

Common problem. It is the O-rings on the EATC (Electronic Automatic Temperature Control). PM "fastblackmerc" or "03mmmonroe" for info on the fix. Takes about 20 minutes to replace all 8 O-rings for a pro like Russ.

Here is some info here >>>> http://www.mercurymarauder.net/forums/showthread.php?t=74634&highlight=O-rings

Do it yourself fix >>>> http://www.mercurymarauder.net/forums/showthread.php?t=36922
BlkRauderMatt
06-07-2012, 04:22 AM
Awesome! Thanks for the quick response Bluerauder!
fastblackmerc
06-07-2012, 04:45 AM
Common problem. It is the O-rings on the EATC (Electronic Automatic Temperature Control). PM "fastblackmerc" or "03mmmonroe" for info on the fix. Takes about 20 minutes to replace all 8 O-rings for a pro like Russ.

Here is some info here >>>> http://www.mercurymarauder.net/forums/showthread.php?t=74634&highlight=O-rings

Do it yourself fix >>>> http://www.mercurymarauder.net/forums/showthread.php?t=36922

I can replace the o-rings for you.

FYI.... Russ (03mmmonroe) doesn't do any repairs via mail....... I do.
CBT
06-07-2012, 06:17 AM
So, under normal or hard acceleration, around 50-65 mph when I have my air conditioner on, it will switch from my a/c blowing in my face to going to the defrost vents..

Nothing on the dash changes when this happens, the air just switches from blowing out the vents to the defrost vents. Not sure why this is happening.. Any thoughts?

Thanks!

How long does it stay that way? Doesn't the computer cut parasitic load under pedal stabbing time? If it just happens and switches back, mine does it. If you stomp the gas and it does it but does not return to normal, I don't see how that is the o-rings. But changing them is cake, go for it.
fastblackmerc
06-07-2012, 06:56 AM
How long does it stay that way? Doesn't the computer cut parasitic load under pedal stabbing time? If it just happens and switches back, mine does it. If you stomp the gas and it does it but does not return to normal, I don't see how that is the o-rings. But changing them is cake, go for it.

The A/C shouldn't switch from vents to defrost under acceleration. The computer will shut off the A/C compressor under heavy acceleration though.
CBT
06-07-2012, 06:59 AM
The A/C shouldn't switch from vents to defrost under acceleration. The computer will shut off the A/C compressor under heavy acceleration though.
And the factory safety default is to defrost the windshield, correct? That's why I asked him it it switches back.
fastblackmerc
06-07-2012, 07:02 AM
And the factory safety default is to defrost the windshield, correct? That's why I asked him it it switches back.

Correct... fail safe is heat & defrost.

Probably the o-rings.... just like the headlight relay in the LCM.... just a matter of time till they go bad.
BlkRauderMatt
06-07-2012, 08:32 AM
Yes it does switch back after I let off the gas.
CBT
06-07-2012, 08:55 AM
Yes it does switch back after I let off the gas.

Then I don't see how this is an o-ring issue. But, the swapping of them is easy enough to try it and see if you just want peace of mind, go for it.
IwantmyMMnow!
06-07-2012, 09:02 AM
I seem to recall mine doing the same as OP's, then within a couple weeks, air was coming out of defrost/floor vents only. Had my EATC o-rings fixed by FBM and haven't had any issues since then...WOT or 'normal' driving...
Bobmiddle
06-07-2012, 10:03 AM
under hard acceleration the motor pulls more vacume and the EATC is vacume controled. With more vacume it is pulling air through a cracked o-ring and when you let off crack seal up makes sence to me???
IwantmyMMnow!
06-07-2012, 10:23 AM
under hard acceleration the motor pulls more vacume and the EATC is vacume controled. With more vacume it is pulling air through a cracked o-ring and when you let off crack seal up makes sence to me???

I'll buy that for a dollar.

...or 8....or over 9,000....
Blackened300a
06-07-2012, 11:08 AM
Then I don't see how this is an o-ring issue. But, the swapping of them is easy enough to try it and see if you just want peace of mind, go for it.

The engine is a air pump, the vacuum it produces is used to hold open the doors between defrost,vents and floor. Thats why you sometimes hear that little burst of air when selecting. Now if you have leaking O rings, the spring will overcome the vacuum pressure and close the door and activating the default defrost setting. Trucks use air to actuate the doors. If there is a leak in the dash, it goes to default defrost.
It's very likely the O rings are at fault.
marauder410
06-07-2012, 11:13 AM
just give the o-rings a try, i just did this 4 days ago and took me a little over a hour.

it was only 4 o-rings not 8 like osme1 has said above
Bluerauder
06-07-2012, 11:16 AM
It's very likely the O rings are at fault.

My MM had the exact same symptoms as the OP last year. Russ did the "O" ring fix for me at MV9 in Harrisburg/Hershey in front of the hotel on Sunday morning. In and Out in 20 minutes and not a problem with A/C since.
Richy04
06-07-2012, 09:01 PM
What kills the O rings is the 10 percent Ethanol in the gas, when you take them out they are hard as a rock. The minor amount of fumes which make their way into the EATC when the vehicle is off definitely makes em hard.
Vortech347
06-10-2012, 05:33 PM
The one in my car does this. I have a backup I'm going to send to fastblackmerc and see if he can fix it.
RF Overlord
06-10-2012, 07:00 PM
What Bobmiddle and Blackened300a said is exactly correct.

When you open the throttle, intake manifold vacuum goes down, all the way to zero at WOT. The square plastic box on top of the driver's wheel well is a vacuum reservoir to maintain vacuum to the EATC system. If the o-rings in the EATC leak (or the check-valve is bad), vacuum will bleed down during acceleration causing the various doors to go to default position. Common problem...