I'm not new to cars in general, but absolutely new to this one... Whenever I accelerate my wife's 2003 Grand Marquis (at a lite of coming off a stop) the Air Conditioning air flow switches to defrost. It returns to normal after the throttle is backed off and the engine builds vacuum back up. Most cars have a vacuum storage canister or tank with a check valve to supply vacuum during the engine gaps. I've looked everywhere and can't find the tank or check valve... Can anyone help me out.

 

The check valve for the AC system may be under the dash. The vacuum reservoir may be tucked under the bumper cover up front or mounted to a wheel well under the hood. Usually when I've had that problem with any vehicle, there's a massive vacuum leak somewhere around the engine (usually in the air injection system on the vehicles I drive). since it's a later model, you may need to check all the vacuum lines to make sure nothing broken/disconnected as well as breather lines and PCV valve(s). If any of these are letting a lot of blow-by or leaks happen, ten you'll need to fix/replace it.

 

Found it, the vacuum reservoir is a 6 X 6 X 3 black plastic box mounted on top of the left side wheel well. It had a crack next to the mounting stud. Trying JB Weld, may or may not work on plastic.. If not off to the dealer... Thanks, Bob D.

 

as long as the surfaces are properly cleaned off and then allowed to cure completely, it should work.

now whether or not the plastic will be good enough to not break again is anyone's guess.

 

Hello,

Can you send a picture of the location of the vaccume reservoir? I have exactly the same problem with my 2003 Grand Marquis.

I appreciate the help.

 

Here's a pic, it's the box on top of the wheel well. It has two studs on the bottom with 7/16 nuts accessible by reaching in over the tire. What happened to me was the car hit a curb, blew the tire, bent the wheel and apparently the suspension design allows the wheel to hit the plastic wheel well. You can see the crack, the tire also hit the reservoir mounting stud and cracked the reservoir. If your reservoir looks OK, you can pull the vacuum line into it (lower left of box). If you apply a vacuum (suck in) to the hose it should hold vac if the check valve is OK. The check valve located directly behind the engine on the firewall prevents vac bleeding back into the intake manifold when the engine is under load or turned off.
IMG_0452.jpg?t=1242226920

 

Thank you for the picture. I assume I need to take out the module, to look for cracks in the bottom ? I checked the top portion of it, and the part looks intact. Another thing I noticed is that the control starts acting up only when the car has been idle for a while (at night, after I get out of work). After a while, the control returns to normal. It may be a useless clue, but you never know.

Thanks again!

 

i just went though simuler proublem with my 03 it was the control head vac valve was leaking ..under accell it would go from vent to def .got use one did same thing so got new one all fixed

 

Thank you! Where is the control head vac valve is located? If you have a Ford P/N to share, it would be great.

Thanks Again! You guys are awsome!!
Frank

 

its the control panel for your cilmate control in the dash ..and bummer part is ya cant just change the valves gotta change the whole thing $1000 cdn