Why does my 2005 Marquis blow high heat no matter what setting I have it on?

Asked by Mar 30, 2014 at 07:33 PM about the 2005 Mercury Grand Marquis

Question type: Maintenance & Repair

My 2005 Mercury Grand Marquis had a clicking sound with the heater blowing and then it quit but now I only get really hot air blowing out.  Even when I put it on A/C, Max A/C, Vent, etc.  Also, changing the temperature setting doesn't change the workings.  It is just always really hot air.  The only way to stop it is turn it all off.  What is the problem?

28 Answers


Press the OFF and FLOOR buttons simultaneously, release, then within two seconds press the AUTO button. if you get a code that says 24, 25 it is your blend door actuator control. of it says 888 it is not the blend door .If you press vent , floor and the hot air still comes out of the defroster then i would think that your control head went bad. which can be found e-bay at a reasonable price its normally a repair service running from 150 and up . still better than the 800.00 the dealer wants If it is your blend door the entire dashboard has to come out to repair it.. As i had to do with mine

33 out of 33 people think this is helpful.
Best Answer

Well, the dash doesn't have to come out but it isn't pretty. Remove the Glove Box, the passenger side air bag, the passenger's side vent and the ducting to the vent for access. (Here's the ugly part) drive a 3" wedge between the evap case to lift up the case enough to get an 8mm wrench. There's 3 screws that hold the actuator in place: 2 you can get to - the one in the back is another story. You can remove the 2 screws and break the tab off of the motor. Leave the screw in place but back it off a couple of turns. Cut the loop on the new actuator for that 3rd screw. Don't worry about cinching it down - it will stay in place. Plug in the new actuator and reverse the disassembly of the dash and off you go - with sore fingers, scratched up arms and saving several hundred dollars - in less than half the time to remove the dash. I said it wasn't pretty.

17 out of 17 people think this is helpful.

My initial problem was when I turned the temperature control from 60 to 72 degrees (automatic a/c heater unit from Mercury). It immediately turned to hot air and wouldn’t change temperature even though I turned it back down to 60 degrees. It just blew out about 90 degree air. I figured it wasn’t low Freon as it happened too quickly and only with the flick of the switch. I’ve turned the car on, off, pressed all the buttons, and then went back to the car a day later and no success. I flipped on all the buttons, raised and lowered the temperature control, and nothing worked. Like many other times I’ve had problems, I disconnected the battery terminal for ½ hour to reset the black box. After the ½ hour the A/C came back to normal operation and ice cold air once again. Disconnecting the battery terminal for ½ hour has worked in so many occasions, whether it’s a high idle or another malady. I’m not saying it is the problem with your car but it’s the cheapest way to see if it works for your problem. Don’t pooh pooh it until you try resetting the black box.

15 out of 15 people think this is helpful.

Rich, I press the button sequences and it went into its diagnostic mode. I got an 888. I had to shut the car off to get it out of the diagnostic mode. When it restarted my ac was working!!! I don't know if it was just an electronic hicup but we'll see how long it stays fixed Thanks for the great input.. Ron

7 out of 7 people think this is helpful.

I'm taking my car to the dealer to make them do it. I don't care what it cost. I want my shit working exactly the way it's suppose to work F that.


To the guy above who said to press the floor button and the off button at the same time and then press auto… What in the hell are you talking about… That does nothing… Cargoes of the dealer

3 out of 3 people think this is helpful.

ATMTH400 Those instructions are for one of those climate control center units. May be different for other units. (see attached image) My climate control center was also stuck in the heat only mode. no matter what it was set on except off. Before I put mine in the diagnotic mode I unhooked the negative battery cable for 5 minutes. Then I turned the power on and followed those instructions and the screen of the unit went into a rotating circle mode for about a minute before it showed a code. Once I finished the unit went back to working properly and has for the last 6 weeks now. The dealer looked at mine prior and charged $150 to say it would cost at least another $650.00 to tear apart the dash and replace a part (the blend door actuator) that wasn't even bad. I'm glad I didn't waste the $650.00. I picked up a spare climate control unit at the bone yard prior to it fixing itself. If yours doesn't self diagnose then your unit might be bad. I would try a bone yard.

7 out of 7 people think this is helpful.

Hi Ron. Sorry to them other guy for the harshness but I just rebuilt my climate control by putting in new o rings. My issue is when I press defrost only it comes out of vent and does not switch to floor only at all. I need my blend door or the motor for it replaced. I'm just taking it to them I don't care about the cost. Lol. My limit for this is $1000.00!

2 out of 2 people think this is helpful.

I could live with it cuz I still have ac and I do get enough air to defrost the windshield but want it to be perfect. I just got this car and it's in perfect condition. It's the Ultimate LS with the handling package.


As I understand, the O-ring replacement will fix the problem of switching from defrost to floor to vent. Those doors are vacuum activated. The door that closes to prevent the heat from coming into the car is electric operated. To replace that the dash has to be taken apart. The diagnostic check codes tell you if your blend door needs to be replaced. Apparently the dealership that looked at mine didn't know that as they took some of the dash apart before they mentioned the cost to do the whole job. Later when I ran the diagnostic test it told me the blend door was ok and it turned out it was. I think the computer in the system had a static charge throwing it off and when I unhooked the cable for 5 minutes it dissapated. Letting it run diagnostics let it reset. Similar to what you do when a home appliance gets confused. Unplug for 5 minutes.

5 out of 5 people think this is helpful.

I ended up haviing the dealer replace my air box. $1300.00 later. So i rebuilt the head unit dealer did the air box. But when i got my car back they damaged my door jams. They fixed them tho.


I lost the AC last summer so the control was off until recently. When I turned it on for heat, I got gobs of heat at full fan with no temp control. Thanks to this thread, I pressed the buttons and it came up 888 so I disconnected the battery for 1/2 Hr. Everything is fine now. Thanks to everyone, you have saved the day for at one person.

3 out of 3 people think this is helpful.

CalSteve. Glad to hear it worked for you too. My AC has worked all summer and it was a hot one this year so I was glad. Ron

1 out of 1 people think this is helpful.

A bad battery or battery connection can cause this problem. That was my problem.

Mine is a 2007. Same problem with constant heat. I took the dash out. When I was too tired to continue I went in and sat at the computer. Browsing around I ran across a guy that had his battery go bad and it when he replaced it the problem was fixed. The next morning I disconnected the negative (ground) from the battery for longer than 5 minuted. When I put it back and started the car the diagnostics gave me another code 25. The heater door was still stuck. I shut the control off and back on and the problem was fixed. If I tried the battery first I could have saver 12 hours.

I have repaired the climate control on a 2005 and on a 2010. takes about 1.25 hours and costs about $2.00 dollars for the o-rings. They both worked perfectly when I was done. Now a have a friend that keeps getting hotter after it reaches its desired temp on a 2010. I will try some of the knowledge I have learned here. Don G


Don, Glad to hear you solved your problem. Most of the climate controls doors are vacuum operated, and you can usually hear them open and close as you change the settings. of the climate control from defrost to floor to vent. If the doors are not switching, the o-rings will likely fix that issue. When you look at your friends car, check to see if his doors open and close when changing the settings. If they do, then try the battery cable and diagnostic option mentioned above before rebuilding the o-rings. Might save some time. The door that closes off the heater core and opens to the AC is electric and rebuilding the o-rings will not have any affect on controlling that. In some cases the climate control computer seems to loose contact with either the door or the temperature sensor in the climate control unit and it just stays in the heat mode no matter if in vent, defrost, AC, etc. Unplugging and rebooting seems to work in some cases, just like your home computer like appliances.

1 out of 1 people think this is helpful.

Mine has had both the control module problem: A/C blows through defrost or floor not from mains then after replacing that(which really only requires 4 new o-rings) it started blowing full heat out of the vents, not warm air, but full heat. It originally happened with a flapping/clicking sound, then the sound stopped after a few weeks and it was just full heat. I disconnected the positive battery cable and waited 5 minutes or more, reconnected it and started her up. Cold air came out of the vents and the clicking sound is back! So at least I can be confident that it's the blend door actuator for ~$45. The dealer says out-the- door cost for the job is 2.2 hrs labor and $109 for the part, total $384. Not sure they know how hard it is to do this job. I was totally impressed that disconnecting the battery had an effect like this. I don't know what that diagnostic mode thing is, mine wouldn't do that. It's an '04 LS premium Grand Marquis by the way with the automatic temp control.


I am amazed that everyone doesn't just do the easy step first ( disconnect battery cable for 15 minutes, then reinstall), then proceed if they want more work done. Many problems get fixed by just disconnecting the battery cable, rebooting the memories of many parts in the car. Fast, slow, or rough Idle, rough running, A/C/heat problems, and a bunch of other problems get fixed by simply disconnecting the battery cable (rebooting the systems). It may not relieve your problem but then, it may....

2 out of 2 people think this is helpful.

Most of the blend doors are vacuum accuated however the louver that shuts off the heat is electronic. This one is very difficult to get to and requires the dash to be taken apart. Usually about a $900 job. Make sure they do not just do that without your blessing. There may be something in your ductwork blocking the door from closing causing the clicking. Also try running the diagnostic check on the climate control just in case it just needs to reset. (Press the OFF and FLOOR buttons simultaneously, release, then within two seconds press the AUTO button. if you get a code that says 24, 25 it is your blend door actuator control. of it says 888 it is not the blend door )

thanks, that diagnostic thing (pushing the OFF and FLOOR, and so on) doesn't seem to happen on my '04, I tried it with the engine running, in accessory mode, off, etc... Pretty sure the blend door actuator is the problem. This guy shows a way to take it off with minimal headache. I know it's a big job, but oh well https://www.youtube.com/watch?v=7RFH0Ue-bnQ


David, I'm surprise the diagnostic test doesn't work as it worked on my 2004 Grand Marquis. Before I learned of the test I spent many hours at junk yards experimenting with trying to remove the actuator. The screws that hold it in place have to be access from on top of the actuator and there was only about 3/4" to work in. I could not get my hands let alone hands with tools in there. I looked at cutting the duct work and that still did not get me anything. If you are getting a clicking sound it does sound like a broken tooth on a gear in the actuator, Remember you are working in the area of an airbag so be sure to disarm that. I'm glad I did not have to replace mine in the end.

Wow richs answer,pressing off floor then auto,reset my ac .


My 08 Merc was blowing cool air last Thursday and then it stopped and began blowing hot air. Could not stop it. Checked out all relays with meter with the use of my car self help maintenance manual picturing all the fuses and relays. Watched YouTube sites and this site. Decided to pull the neg. cable off like I did in the past with other vehicles. I did check my AC coolant level with my gauge hose and put a few more ounces in but the clutch did not engage on the compressor. So I went online and read some views.Thanks guys for the reminder and heads up on that DYS task.Pulled the neg. cable for 1/2 hour. Started the car. Set AC on Max @ 65' not 60' The outside temp was 70' and the clutch engaged and super cool air started pouring out! The computer rebooted itself and I'm sure the extra coolant helped also. It needed to reboot just like my laptop when it freezes up. Forced shut down and restart brings it back from the dead. Thanks guys for the reminder. I was ready to go to the Dealer. Hope this helps other people with hot air pouring out of their vents. Check coolant level, examine the clutch on the compressor, check out the appropriate relays tied to AC and then pull the neg. cable and go from there. Of course it could be something else. Trouble shoot! Mike in upstate NY


Gurunqfl, glad the removal of the battery cable worked for you. My feelings are always "KISS". The old saying, "K"eep "I"t "S"imple "S"tupid. We all have to do the easy solutions first. I always remove the battery cable first for all problems with the car. It fixes a multitude of running problems. Too many years doing the complex stuff first.


My rejoicing has ended. My 08 Grand Marq is back blowing hot air through the AC. Removing the Neg. cable only worked for two days. I think its something else. I will see what the Dealer says. Unhappy. Mike in upstate, NY

1 out of 1 people think this is helpful.

Mike, The good news is your AC is still working. Besides unhooking the battery cable, after you reconnected, did you try running the diagnostic check? (Press the OFF and FLOOR buttons simultaneously, release, then within two seconds press the AUTO button. if you get a code that says 24, 25 it is your blend door actuator control. of it says 888 it is not the blend door ) That way can tell you if it is the actuator for the blend door. I suspect your Control module is bad since the actuator worked for a couple of days. Sometimes you can find a used control unit from a "you pull it" like junk yard for $20 or so and they usually guarantee them for 30 days. Pretty easy swap out. Hell practice at the junk yard. I just feel the dealerships will run up a bill and not fix anything. That was my dads experience with this problem.

I just tried disconnecting the battery and the button press and the A/C came on for about a minute then the little heater door started opening and closing repeatedly. Then hot air again. Is this something I can fix myself?

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