2005 Mercury Gran Marquis air conditioning

[B.G. Smith]

The system is charged and cools fine when the air is going where it is supposed to go. With the switch on automatic when I accelerate a little hard the doors switch to the floor and no air from the dash, get to cruise speed and it comes back to dash vents. I think the controls are electric operated rather than vacuum. Any ideas? bg

 

[DonFitzwater]

Sounds like a classic vacuum leaker. You'll likely have to hook it up to a smoke machine and find the leak....................some cars can be a royal pain in the arse so good luck!

 

[Wayne M.]

If you do have a vacuum problem, and it relies on the engine for the vacuum, you'll have a MIL for lean banks.

 

[PBJ2500CTD]

I'll go along with DFitzwater and say there is a vacuum issue; more than likely a bad vacuum check valve in the HVAC's vacuum syatem. Years ago I had the same experience with a few older model Fords. A couple of them had the 25 cent check valve built onto the $25 "can-o-beans". Easy fix, once you find it.

 

[PBJ2500CTD]

BG,

Check this out - http://www.justanswer.com/mercury/5671n-mercury-grand-marquis-a-c-vent-does-not-blow-vents.html

Check valve is item 17 on one of the diagrams.

 

[B.G. Smith]

Thanks for the replies, I went out last night with a flashlight and looked for a vac. line or the reservoir. No find. Went back this morning and still can't find it. It does have vac. booster for brakes. I ran the self diagnosis and got the 888. Anyone know where the line enters the dash? Thanks again. bg

 

[PBJ2500CTD]

BG, here is a link describing the location on a 2004. Maybe this will help locate the elusive stuff.

http://www.cargurus.com/Cars/Discussion-t30595_ds595042

Tracy answered 2 months ago You can't. What's going on is a loss of vacuum to your HVAC controls. It's likely that you have a vacuum check valve, vacuum line or vacuum reservoir that is leaking or that has failed. Just left of center, under the hood and attached to the Firewall is a vacuum canister and a "T". Usually, the problem is the check valve (the "T") but could be a broken vacuum line.

Maybe something in this link will look familiar

http://www.justanswer.com/mercury/3pm6u-2008-grand-marquis-ls-when-put-ac-sometimes.html

Better detail here: http://www.fordparts.com/Commerce/C...and+Related+Components&scatId=32211014#Search

 

[B.G. Smith]

Thanks for the links Bruce. I found the vac. cannister, it is directly behind the engine down low and is rectangular in shape rrather than round as I was looking for. Some design engineers must have spent a lot of time figuring out a place to put it so you can't have access to it. I am in the process of trying to find a leak or the problem. The vac. lines enter the cabin on the drivers side just to the left of centerline. Thanks again. bg

 

[PBJ2500CTD]

Your symptoms showing up under load put the check valve under suspicion over most other possibilities. Kind of like the older cars with vacuum wipers; worked great at cruise and coast...but accelerate from a stoplight or hit a long hill in a deluge - and experience a super-pooh-nugget moment if you are lucky enough to see that ol' semi crawlin' up the same hill. Some cars and trucks even had a manual lever to use in low vacuum situations.

 

[B.G. Smith]

I got under the dash (some) enough to check the vac. at the brake release, shows about 15" and holds when I kill the engine. I also checked it at the recirculating door and it only has about 6" with engine running and goes to zero when I kil the engine. I'm thinking it may be in the control module. If I remember correctly it was replaced under warranty when it wouldn't put heat to the floor in winter. And yeah, I'm old enough to remember the vac. Wipers. bg

 

[B.G. Smith]

Back on the AC problem today. I pulled the control module and unplugged the vac. connections, hooked vac. gage to the black line, ran engine, pulled about 17-18" vac. shut down, held vac. So I decided the problem is in the module. Not having access to a new module or repair parts I re-installed the module. Woops, no air out the vents at all, everything going to defrost/floor. Pulled module back out ond noticed that the rubber connector with all the vac. lines in it was bowed out away from the module. Repositioned it and now everything works like it is supposed to. The car sits outside in the sun and I suspect the heat caused the rubber connection to soften and warp. It doesn't fit very tight and I suspect I may have to revisit it again. Thanks for the help, saved me a trip to the dealer. bg

 

[PBJ2500CTD]

BG,

That's great! The best fixes are the zero $, or low cost ones.

 

[B.G. Smith]

Update: Repositioning the vac. manifold only worked a short time. When car was cool inside it worked pretty well/often but when you got into car and it was hot inside you had to ride with the air going to floor and defrost a few miles. Bruce, in looking at your suggestions/help I found a youtube vidieo on replacing the "O" rings in the module. I ordered the "O" rings and did the repair and all is well for about ten day now. Spent less than ten dollars but if my labor was worth anything the bill was pretty high. Thanks again. bg

 

[PBJ2500CTD]

That's great to hear. Quality labor does have its price. At least you know the job was accomplished to the highest standards.

 

[fest3er]

That's great to hear. Quality labor does have its price. At least you know the job was accomplished to the highest standards.

Well, at least to his own standards.