Heater fan stuck on high speed


Asked by Sep 27, 2015 at 07:06 PM about the 2004 Mercury Grand Marquis

Question type: Maintenance & Repair

Can not change the blower speed from high ---- it will even blow when the key is in the acc prosition

10 Answers


sounds like the switch is bad...anyone else out there want to add anything>?

2 of 2 people found this helpful.

Should it not cut off the power when the key is in the acc position ?

1 of 1 people found this helpful.

Is there a relay or temp-speed secencer that may be stuck ?


There is a resistor that controls the blower motor speeds. When you turn your switch low, medium, high, the resistor regulates the amount of voltage to the blower motor to acquire the desired speeds. In the accessory position the blower motor should be off. When mine went bad the blower motor kept on running on high, even with the key out of the ignitionl

6 of 6 people found this helpful.

If you have automatic climate control it's going to be the control module in the engine compartment on the firewall. When they fail you either get constant high speed or no blower motor at all. HTH. -Jim

8 of 8 people found this helpful.

Glad to learn of the above. My fan blows high even in the Off position! Does the whole control module have to be replaced, or can resistor be replaced.


Chances are the blower motor resistor would be the culprit there Colin. Not to say the fan switch may be bad without looking at it.

1 of 1 people found this helpful.

In order to keep driving without the high fan speed irritation, I removed two fuses in box under dash. There is a rather. large relay in box under hood- warning label states only qualified technician should replace, so since there are 5 male fittings and not knowing what else might be affected, I left it alone, just pulled fuses. Owner's manual shows chart of functions and placement by number. Car ran fine without fan blowing. As long as car speed was sufficient to move air, cabin was warm. Today I pulled the resistor unit to see if there was water or rust since the problem occurred when sleet and snow hit us.. .had to pull both heater water hoses. There are rows of vanes or ribs as on air-cooled engines with some type of large button in the center, all sitting on what looked like a circuit board- all looked dry. I used a hot air blower for about 30 seconds, just in case there might be some moisture in there, hoping that might cure the problem so as.to avoid buying a replacement at this time. So, put it all back together just as darkness was falling. Will know tomorrow if my climate control is back to normal.


It worked! Praise God for giving me a mind to think and reason. I replaced the two fuses, started the engine & checked fan speed & other settings. Great day! Canceled order for replacement resistor & saved myself $35 plus any potential shop charges.

Hey Colin, it appears I have the same issue with my Grand Marquis as you did. Which two fuses did you replace to fix the issue? Thanks in advance!

Your Answer

Grand Marquis

Looking for a Used Grand Marquis in your area?

CarGurus has 1,521 nationwide Grand Marquis listings starting at $995.


Mercury Grand Marquis Experts

  • #1
    Tracy Hooks
  • #2
  • #3
View All

Related Models For Sale

Used Lincoln Town Car
13 Great Deals out of 1,587 listings starting at $1,200
Used Ford Crown Victoria
3 Great Deals out of 877 listings starting at $2,000
Used Chevrolet Impala
506 Great Deals out of 32,381 listings starting at $1,000
Used Ford F-150
3,046 Great Deals out of 230,459 listings starting at $1,300
Used Chevrolet Tahoe
822 Great Deals out of 40,004 listings starting at $1,700
Used Chrysler 300
317 Great Deals out of 19,548 listings starting at $1,400
Used Mercury Marauder
30 listings
Used Ford Mustang
341 Great Deals out of 42,379 listings starting at $1,488
Used Ford Taurus
194 Great Deals out of 16,161 listings starting at $1,200
Used Honda Accord
818 Great Deals out of 88,083 listings starting at $1,444
Used Chevrolet Silverado 1500
2,684 Great Deals out of 157,095 listings starting at $1,000

Used Cars For Sale

2011 Mercury Grand Marquis For Sale
21 listings starting at $4,495
2010 Mercury Grand Marquis For Sale
7 Great Deals out of 78 listings starting at $2,290
2009 Mercury Grand Marquis For Sale
80 listings starting at $3,200
2008 Mercury Grand Marquis For Sale
3 Great Deals out of 132 listings starting at $2,990
2007 Mercury Grand Marquis For Sale
116 listings starting at $1,600

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.