No heat?

Tiny
VMORRILL
  • MEMBER
  • 1999 MERCURY MOUNTAINEER
  • V8
  • 2WD
  • AUTOMATIC
  • 13,000 MILES
How do I determine the culprit. The fan works, but there is no heat. There has not been any leaks. The heater core or the blend door actuator or simply a fuse?

Thank you,
Vic
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Friday, December 11th, 2009 AT 11:34 AM

47 Replies

Tiny
BLACKOP555
  • MECHANIC
  • 10,371 POSTS
Only way to find out is feel the heater core hoses.

cold or warm heater core hoses possible plugged core, air in lines or bad heater control valve if equipped.

This guide can help us fix it

https://www.2carpros.com/articles/car-heater-not-working

if theres a difference in temps between hoses could be a bad/plugged heater core, air in lines or plugged lines.

if both hoses are hot its in the dash.
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Friday, December 11th, 2009 AT 3:19 PM
Tiny
VCLINE
  • MEMBER
  • 1 POST
  • 1999 MERCURY MOUNTAINEER
Heater problem
1999 Mercury Mountaineer V8 Automatic

We have replaced the coolant and the thermostat but still have no heat in this vehicle. It blows cold air only. Can you suggest what else we should look at?
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
WRENCHTECH
  • MECHANIC
  • 20,758 POSTS
With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both hot to the touch. If they are.

The temperature is controlled by the use of an air mix door that is operated by an electric motor/actuator. This door can be jammed or the actuator can be inoperative or have stripped plastic gears internally.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
GREGLOKEY2002
  • MEMBER
  • 1 POST
  • 1999 MERCURY MOUNTAINEER
Heater problem
1999 Mercury Mountaineer V8 Two Wheel Drive Automatic

I turn my heater on it only blow cold air, no heat. What could cause this to happen?
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 107,922 POSTS
Hi:
First, is the engine warming to a normal operating temp? Second, with the engine running, hot, and the heat on, feel both heater core hoses. They should both be hot. Finally, is the coolant level full?

Let me know what you find. IF these things are all ok, we will need to look at the blender door.

Joe
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
GABBY529
  • MEMBER
  • 2 POSTS
  • 1998 MERCURY MOUNTAINEER
  • 5.0L
  • V8
  • AWD
  • AUTOMATIC
  • 220,000 MILES
I had my heater core replaced. Now when I turn heater on it only blows from defroster even when I have the setting on floor
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,606 POSTS
Take it back to the people that fixed the heater core or you can do this yourself. Check to see why mode door isn't getting vacuum as it may be disconnected or a hole in line from heater core replacement.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
GABBY529
  • MEMBER
  • 2 POSTS
Ok thank you
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
2CP-ARCHIVES
  • MEMBER
  • 4,544 POSTS
  • 1997 MERCURY MOUNTAINEER
  • 175,000 MILES
No heat. Ballpark figure for fixing
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,606 POSTS
First do soem stuff yourself, see if both hoses leading to heater are hot it could be no vacuum to water valve on engine. Check for a vacuum leak and check to see if vacuum motors on heater are getting vacuum or are working if they are. Then you need to go from there. Pic enclosed on lh side.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
JUSTINW1
  • MEMBER
  • 1 POST
  • 1997 MERCURY MOUNTAINEER
Heater problem
1997 Mercury Mountaineer V8 All Wheel Drive Automatic 190k miles

After letting my truck warm up this morning I got in and turned the heat off because it was insanely hot, and after I got about ten minutes down the road it cooled off enough to turn it back on and when I did it worked for about 30 seconds and went to cold air. I believe it was just blowing outside air because my a/c has been torn up since last summer so it obviously wasn't a/c air coming out. After the heat went out I noticed a soft, constant clicking coming from what seemed like deep in the dash just to the right of my steering wheel, but it very well could have been coming from under the hood, it was hard to tell. This clicking noise goes whether the heater is on or off, constantly as long as the car is running. My first thought was thermostat but I drove the truck for 3 hours after that happened without stopping and the engine temp never fluctuated so now I'm thinking it may be my heater control valve. Does this sound like a decent assumption? If so is there a way to tell if it is bad by just looking at it? I'd hate to buy one and put it in for nothing. Any info would be much appreciated, if you think it could be something else please let me know. Thanks in advance for any advice.

EDIT:
There is a possibility this clicking noise was present before the heat went out, but I didn't notice it if that was the case.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 107,922 POSTS
It sounds like the blend door is stuck. It is what determines if you get AC or heat. It is under the dash and half of the dash needs to be removed to access it. That is my first guess based on your discription.

Let me know what you find.
Joe
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
BECKYCOLLINS
  • MEMBER
  • 1 POST
  • 1997 MERCURY MOUNTAINEER
  • 80,000 MILES
I turned the heater on one morning and was working fine. The next day I turned it on and it was blowing cold air. I have replaced the thermostat and still won't blow out hot air. Fan works fine. A hose was also replaced due to wear on hose. Still won't work. I can't figure out what is wrong, could it be the core in some way and how would I know that is the problem
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Do the heater hoses get hot? Does the engine reach normal operating temp? Another possibility is an actuator under the dash.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
Just to add, if both heater hoses are hot, I don't think it is the heater core. You could flush the heater core if you wanted?
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
RJMILLSBJKL
  • MEMBER
  • 2 POSTS
  • 1997 MERCURY MOUNTAINEER
Heater problem
1997 Mercury Mountaineer V8 Four Wheel Drive Automatic 125k miles

1997 Mercury Mountaineer, Heat problem. Occassionally a delayed flapper could be heard opening from underneath the dash and then the blower would come on. The Blower had only worked on high speed setting. Now Nothing! No Blower, No Flapper noise. No Heat At All. Any Cure?
It appears to me the blower motor is controlled by the flapper opening. Sometimes the rear heat will blow warm without the front blower actually operating.
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
RICKMAR
  • MECHANIC
  • 170 POSTS
When your blower motor was working in only one speed "High". It is very possible your blower motor resistor is either stuck or needs replacement.
If you can repair it yourself that will save you some money. Here is what you need to do.

Remove the speed control servo.
Disconnect the electrical connector.(1)
Remove the bolt. (2)
Position the speed control servo (3) aside.


https://www.2carpros.com/forum/automotive_pictures/433905_Servo_Motor_1.jpg



Remove the coolant/washer reservoir.
Remove the two screws and the two nuts. (1)
Move the coolant/washer reservoir (2) aside.


https://www.2carpros.com/forum/automotive_pictures/433905_Windshield_washer_res_1.jpg



Refer to the sketch below for the blower motor resistor location.
You will see the blower motor resistor (1) just below the vent hose. The arrow is pointing at the blower motor housing.

Turn the heater fan speed selector on "High".
Turn the ignition "On" but do not start the engine.
Get a long screwdriver or something similar and place it against the resistor housing.
Give the resistor a slight tap, listen to see if the blower motor is working. If it isn't, give it another tap.If it is not working, give it one final tap.

If the blower motor is still not working the resistor needs to be replaced.

To remove the resistor:
Disconnect the electrical connector from the resistor.
Remove the two small bolts.
Remove the resistor and replace it with a good one.

You can buy the resistor "new" at an automotive parts store or if you have a "Junk Yard" or "Auto Salvage Yard" near you, you can pick a used resistor up from them and save some money


https://www.2carpros.com/forum/automotive_pictures/433905_Blower_motor_resistor_copy_1.jpg



I hope that helped you out;
Rick
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
RJMILLSBJKL
  • MEMBER
  • 2 POSTS
Thank you Rick for your detailed response. I had to run to the junk yard to grab a three knob controll for inside the vehicle because I had broken one of the knobs, As I was there I did grab a resistor from that vehicle and installed it. The problem continues! No Fan. So, I ran a wire from the battery to the blower motor as it was in place and spliced into the positive wire of the blower to see if the blower would work. The blower works. (High Speed of Course)
Some where between the inside fan control and the blower I've lost power to the blower. I followed the blower motor wire to the frame of the vehicle to a black box with three or four contacts inside, which is located on the passenger side closer to the front of the vehicles frame. Could my problem be locate in this black box? And would the resistor I replaced it with be bad too?

As I said I spliced into the blower motor wire from the battery and the blower can be controled from off to on (high speed) from inside the vehicle. I naturally want to control all the speeds and I'm still looking for a solution to the blower not responding to the setting inside the vehicle. As I mentioned before I believe, the blower does not operate on any speed that was set inside the vehicle. It use to work only on high speed before, it stopped working completely.

Fuses inside have been checked

Thank you in advance for your help and expertise!
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Tuesday, July 21st, 2020 AT 11:56 AM (Merged)
Tiny
RICKMAR
  • MECHANIC
  • 170 POSTS
Hi rjmillsbjkl ;
The problem "possibly could" be in that black box.

The resistor is usually always the case 9:1.
There just might be "very slight" chance of (1 out of 9) you did pull a bad relay out at the junk yard.

You mentioned that you grabbed a three knob control so you "do" have the correct resistor that goes with that configuration.
Some mountaineers have a digital "EATC" (Electronic Automatic Temperature Control) and the resistors electrical connector is a little different than the knob type.

I'm thinking the electrical connector may be giving you a problem but not sure... The (resistor you took out of the junk yard)... is it identical to the one you replaced ?
It is now narrowed down to the resistor/ wiring harness/ black box. We have not ruled out the blower motor completely but we should throw that in too just in case.


https://www.2carpros.com/forum/automotive_pictures/433905_1997_explorer_blower_motor_1.gif



Just giggle electrical connector (2) in the sketch above and see what happens.... I will be back later on today.

Rick
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Tuesday, July 21st, 2020 AT 11:57 AM (Merged)
Tiny
SBINGHAM
  • MEMBER
  • 2 POSTS
  • MERCURY MOUNTAINEER
I have a 1997 Mercury 95000 miles it has no heat, and also shows no engine temp on the dash I have replaced the coolant temp sensor. Thermostat and checked the coolant level in the radiator. The blower works properly and Both hoses that go to the heater are hot what next?
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Tuesday, July 21st, 2020 AT 11:57 AM (Merged)

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