Why does my heater fan only blow cold air?

Asked by Sep 14, 2008 at 05:05 PM about the 2001 Mercury Grand Marquis

Question type: Maintenance & Repair

When I turn the heat on in my car it only blows cold air. The AC works just fine and the fan does blow at full power but no matter how long the car has been running for the air still remains extremely cold. We have taken the whole dash area apart and everything works fine so i assume the problem is coming from under the hood.

13 Answers

1,025

If both heater hoses under the hood are hot, the blend door in the hvac plenum is not moving to direct airflow through the heater core. If one is hot and one is not, you have a plugged heater core. If both are cold, you have an air lock in the heater core. Check the coolant level and run veh at 2000 rpm in park with heater on full till you get heat, then top up coolant again. If this continues to happen you are getting air in the cooling system. Only comes from one place -- the head gasket(s) have failed and you are getting combustion pressure pushed into cooling system.

77 out of 77 people think this is helpful.
9,785

You have a heater conrol valve that directs hot water to the heater core. If that valve is faulty it would cause your problem. I would first inspect all the hoses under the hood to ensure that a previous owner has not disconnected the heater core. Also inspect coolant level as low coolant level will effect proper heater function.

24 out of 24 people think this is helpful.
540

I have had this same problem. My car will blow hot air for awhile, then suddenly it will be stone cold. I have had it checked by 2 different garages (one was the dealership). The first garage identified a problem with the rheostat (sp?) which was truly broken, so they put in a new one. Due to the on and off again nature of the problem, this seemed to fix it. When it started blowing cold again, they referred me to the dealership, where they replaced the thermostat (which the first garage had said was okay, but the dealership showed me it wasn't working). The first garage is the guy I trust, and he told me if it wasn't the part he fixed, it was probably the diverter up under the dash and he referred me to the dealership to have that fixed. I think the dealership messed with the thermostat (which worked fine at the first garage) and just replaced that, since it was quick and easy to do and would also be the obvious place for the problem to be. What I get sick of, is being treated like a "girl" who has to take them at their word. I asked to see the non-functional thermostat, but they already had it off the car, so how do I know that was even my thermostat? I asked to see the manager of the service department, and he assured me his staff is honest. Yeah, whatever. The car was blowing hot air at that point so I paid the bill and left. That was early spring, I haven't used the heat again until now and it is STILL DOING THE SAME THING it was doing before I had ANYTHING fixed. I am frustrated, and don't know who to take it to. My father was a career auto mechanic, so I grew up around this stuff and find it infuriating to be treated like a stupid woman who doesn't understand the difference between an diverter, a heater core, and a thermostat. Grrrrr.

54 out of 54 people think this is helpful.
450

11/15/2011 would like to know what you found. I'm now having the same pblm I have not used the heater since last winter...worked fine then. Turned it on for the 1st time this fall season....nothing but cold air. coincidentally the A/C on my vehicle wld not trun off this past Aug. It was repaired/wks good. now 1st time use of Heater. I dont like the where this is going. do not know if these 2 wk independently of each other or if there is a common link.

45 out of 45 people think this is helpful.
365

I had a problem like this w/ my '01 Gr. Mq. Would say first that your vent system air diversion door is not operating properly b/c the vacuum-operated door motor is bad or the vacuum hoses are not all connected, or not properly connected. My vacuum motor went bad and would only open part-way. I first thought it couldn't be the vacuum motor b/c I could hear the door moving when I started the engine. This is the door that deflects air across the under-dash heater coils so you get heated air (or not). So, if the door doesn't move to deflect air across the heater coils you get little or no heat into the passenger compartment. The second possibility may be the most probably if you get no heat whatsoever b/c that means the hot water diversion mechanism (out under the hood) is not functioning, hence hot water is not even reaching the under dash heater coils in the first place. I purchased a vacuum motor at the local Ford dealership ($25 or so)and easily replaced it myself and I'm sure you could do the same with the hot water diversion mechanism under the hood.

34 out of 34 people think this is helpful.
660

How do you determine if its the vacuum motor or a broken door itself?

66 out of 66 people think this is helpful.
340

how come i hear my a/c pump clicking while the heater is blowing. heater works fine just clicking is anoying .my a/c is out of freon but the heater and a/c shouldn't be running at the same time right?

34 out of 34 people think this is helpful.
60

i have a 97 ford explorer xlt 5.0 and tried the door blend and both were cold air no matter what setting the heat was on so i disconnected the ac power under the hood, and it works great so try that bc your ac may be constantly running and if u do the door blend make sure the door is shut for heat :) hope i helped

6 out of 6 people think this is helpful.
40

The A/C compressor will kick on when you engage the defrost to keep the compressor from seizing throughout the winter.

4 out of 4 people think this is helpful.
110

Having the same problem but head gasket is ok, thermostat is ok no water in the oil but when I press on the Gas it blows hot when I let off cold again

6 out of 6 people think this is helpful.
70

SAME issue! I have a 200 merc mountaineer. This is the second time this season. I replaced the following the first time, rad cdp, thermostat, heater core, then finally the control module <-- that was the issue the entire time. So this time i started there, still blowing cold air. My heat was working, i noticed my cap went bead again and i was low on coolent so i topped it off and put a new cap on it. Then My heat went out.. I need help!'

7 out of 7 people think this is helpful.
110

I figured mine out I ran water through the heater core hoses and noticed they were clear, on alot of ford's there is no valve to let the air out. So I ran my truck until I knew the thermostat was open with the radiator cap off , I applied the gas pedal and of course it started blowing antifreeze out I did it twice everything went back to normal immediately. Topped off the coolant haven't had a problem since

3 out of 3 people think this is helpful.
10

yes on some models air will build up and block heater core make sure coolant is full raise front end off the ground rev engine till heat comes on shut engine off lower car van etc fill to top with coolant

1 out of 1 people think this is helpful.

Your Answer

Add photo

Related Questions

  • Cold Air from Heater 3 answers

    I replied to another post regarding this topic but wanted a new thread so maybe I could get a quick reply. I have had my car in twice for this problem and it still isn't fixed. I don't want to take ...

    1997 Mercury Grand Marquis 4 Dr LS Sedan

    -

    Maintenance & Repair

  • why does my air condition keep blowing heat when i turn it on air condition 2 answers

    the air condition keep blow heat even when i turn in on air condition. the compresser is turning, and the lines are cold but the air want come out cold

    1997 Mercury Grand Marquis 4 Dr LS Sedan

    -

    Maintenance & Repair

  • heater blows cold air 2 answers

    1986 Mercury Grand Marquis

    -

    Maintenance & Repair

  • heater fan will not stop blowing 6 answers

    When i turned off the heater the fan continues to blow on my 2001 grand marquis. The display panel turns off but not the blower.

    2001 Mercury Grand Marquis

    -

    Maintenance & Repair

  • Heater 2 answers

    Heater blows cold air replaced heater core and thermostat And flushed radiator and still cold Don't know what else to do

    1999 Mercury Sable 4 Dr GS Sedan

    -

    Maintenance & Repair

Grand Marquis

Looking for a Used Grand Marquis in your area?

CarGurus has 1,796 nationwide Grand Marquis listings starting at $500.

ZIP:

Search Mercury Grand Marquis Questions

Mercury Grand Marquis Experts

#1 Tracy Hooks
Tracy Hooks
Reputation 5,250
#2 kbro
kbro
Reputation 2,050
#3 Js08016
Js08016
Reputation 1,660
View All

Related Models For Sale

Used Ford Crown Victoria
12 Great Deals out of 976 listings starting at $2,990
Used Lincoln Town Car
28 Great Deals out of 1,818 listings starting at $1,995
Used Chevrolet Impala
618 Great Deals out of 29,205 listings starting at $1,300
Used Ford Taurus
194 Great Deals out of 19,158 listings starting at $1,495
Used Cadillac DeVille
6 Great Deals out of 1,606 listings starting at $2,000
Used Chevrolet Tahoe
610 Great Deals out of 27,569 listings starting at $600
Used Ford F-150
2,406 Great Deals out of 208,534 listings starting at $895
Used Ford Mustang
303 Great Deals out of 45,095 listings starting at $2,000
Used Honda Accord
688 Great Deals out of 81,550 listings starting at $1,200
Used Chevrolet Silverado 1500
2,042 Great Deals out of 158,133 listings starting at $1,995
Used Lincoln Continental
3,672 listings starting at $31,815

Used Cars For Sale

2011 Mercury Grand Marquis For Sale
3 Great Deals out of 43 listings starting at $3,900
2010 Mercury Grand Marquis For Sale
4 Great Deals out of 91 listings starting at $4,100
2009 Mercury Grand Marquis For Sale
97 listings starting at $4,299
2008 Mercury Grand Marquis For Sale
6 Great Deals out of 142 listings starting at $500
2007 Mercury Grand Marquis For Sale
3 Great Deals out of 148 listings starting at $2,500