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?

14 Answers

Rich Optional

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

28 out of 28 people think this is helpful.
Best Answer
Tracy Hooks

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.

9 out of 9 people think this is helpful.
Ron Glowen

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

5 out of 5 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

2 out of 2 people think this is helpful.
Ron Glowen

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.

4 out of 4 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.

Ron Glowen

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.

4 out of 4 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.

1 out of 1 people think this is helpful.
Ron Glowen

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.

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