Why is this happening??

[Blackened300a]

For the past 5 days, Everytime I turn on My A/C It Will Blow out the dashboard Vents then stop and start Blowing out the Defrost Vents!! I turn it Off then back on and it will work through the vents for a little while then go through the defrost Vents on its own. If I turn the A/C on Norm and keep the fan low, It will work fine until I go Full Throttle, then it go out the Defrost Vents once again! I was driving on the highway today, the A/C was blowing through the Dash Vents and I noticed that when I give it a little throttle, the A/C wouldnt blow out as much, then when I Let off the gas it will Start Blowing normally. Now Im aware that it has something to do with the Vacuum. But Im Not sure if any of my Mods may be the cause of it. I have installed the PHP Airbox and the PHP Intake Spacer. I have also installed a SCT tune From DR. I wonder if this would create a vacuum problem?? I have Checked all the vacuum lines coming off the Intake Cover As well as following the Vacuum diagram and checked all the hoses. I dont see any leaks or cracks in any of them so Im Puzzled. Before I make a trek to the Dealer, I want to be sure that It wasnt My Mods that cause this. Any Help is appriciated

[bigjohn]

Definitely the signs of a vacuum problem. I've had a number of Fords over the years do this. Since I've only had my MM for a few days I can't begin to tell you where to look. But the way Ford's HVAC controls usually work, no vacuum sends airflow to the defroster outlets. At WOT there is little to no vacuum. When you let off, vacuum returns and your system returns to normal.

There is usually a vacuum resorvoir (the ones I've seen are about coffee can sized) with a check valve on it to supply the HVAC controls with vacuum during WOT so this doesn't happen. Not sure where it is on these cars but it sounds like yours may not be working properly.

[Blackened300a]

Thank you Very Much, I shall try to hunt for the canister. Anything to save me from leaving my car laid up at the dealer.

[Smokie]

Think back to just before 5 days ago, did you do anything under the dash? You may have disconnected a vacuum line, same question for under the hood, any work prior to 5 days ago? There may be nothing broken, just something disconnected.

[fastblackmerc]

Think back to just before 5 days ago, did you do anything under the dash? You may have disconnected a vacuum line, same question for under the hood, any work prior to 5 days ago? There may be nothing broken, just something disconnected.

Yep, it's a vacume leak.

[MENINBLK]

The Vaccuum Canister is on the Driver's Fender liner.
It looks like a component cause it's square, but it has a hose connected to it.
If it is cracked, or the hose is disconnected, then that is the reason
why your vents are acting up.

[ckadiddle]

You guys are way off base with "vacuum leak". It's one of these reasons:
1. Alien abduction of the Marauder to probe it's inner workings.
2. Sunspots.
3. Gamma Rays.
4. Parked too close to a Honda and was affected adversely by Evil Ricer Energy Field.

[CBT]

You guys are way off base with "vacuum leak". It's one of these reasons:
1. Alien abduction of the Marauder to probe it's inner workings.
2. Sunspots.
3. Gamma Rays.
4. Parked too close to a Honda and was affected adversely by Evil Ricer Energy Field.

Just when I thought it was safe to take off my aluminum foil hat!

[Blackened300a]

Thank you Very Much for the Tidbits of Info, I dont think the List of 4 Possible reasons would qualify as Help but it was funny lol

[scareme]

I've been having the same issue and can't find anything disconnected anywhere. Please keep posted if you find the problem, I've actually given up on it since it does work after a little driving for whatever weird reason.

[Blackened300a]

I've been having the same issue and can't find anything disconnected anywhere. Please keep posted if you find the problem, I've actually given up on it since it does work after a little driving for whatever weird reason.

Yeah I will keep you posted. I plan to go through all the vacuum lines and the canister to make sure there is nothing cracked or leaking, then Im off to the dealer for a controller probably. Have you Tried Putting on the Vents, then Switch to the Defrost, then Switch to the Vents again??? On my Car it stays on Defrost and dont switch back to the vents even at idle. I been putting up with it since Its coming out the vents and I have some AC at the time but I do plan to get to the bottom of it Very Soon

[scareme]

Mine won't change do to me playing, only when it feels like it. Once it starts to work it's like nothing is wrong. Usually starts after a few miles of driving???

[Sinister]

When it stops blowing out dash, I figured out that you can turn fan all the way down and when air starts blowing out dash vents again, you can sneak it back up. Sometimes.

[Marauderjack]

HVAC controller......Just had mine replaced for the very same reasons!!

Out of warranty it is over $400......Luckily mine is still a warranty fix.....took me all of 10 minutes to pop it in!! My dealer likes for me to do things like this as in keeps me out of the shop!!

Marauderjack

[Blackened300a]

Nothing like Following up over a year later. I went to the dealer and it was the electric heater control. Basically the dashboard temperature control unit.
Has been perfect since.

I forgot I even started this thread, I started reading it like it was new until I saw my avatar