Strange HVAC issue onmy 98

[BlackIceLSC]

I bought it and the seller fully disclosed "the blend door is broken"

Yesterday I decided to just open the top of the dash(remove message center screen) so I could see the broken blend door actuator.
To my surprise, it is NOT broken, the arm is intact and the motor works as it should.
The metal rod is off because the lower gray arm is broken.

I can move the lower arm about 1.5" down towards the floor/glove box but it hits a "stop" inside the HVAC box...almost like a door hitting the end of its travel.

while working the climate control, I can see the black arm move as it should...and when manually pulling the gray arm down until it stops like the flap/door has "closed", yet I still get no heat. It feels like the temperature is getting warmer a few degrees when I have the gray arm pulled fully closed/against whatever is stopping it.
But what is odd is, if I let go of the gray arm, it returns to the UP position like it is on a return spring =it doesn't stay where I pull it to....and the temperature is only 5 degrees warmer than ambient(if I had to guess)



any suggestions?

 

[billcu]

I happen to have a spare gen 2 HVAC in the basement so I took a look.

The lower door just closes from gravity when the arm is disconnected. The hinge point of the door is where the grey arm attaches. Mine's broken, but I can put a 1/4" extension in and open and close the door manually, it does feel like it could be a spring at the shaft, but it's just the weight of the door.

The door only opens about 2 inches at the far end of it, not many degrees of rotation at the shaft.

Here's a couple photos, open, then closed.

 

[BlackIceLSC]

thanks Bill....I wonder why, then when I have the door DOWN, it still only blows luke-warm air, not HOT....
any thoughts?

and THANK YOU for the photos! It helps me grasp WTH is going on.

I'ts going to be in the 20's this week in the AM and I'd like a little heat...plus I hate to take the dash out to repair it, without knowing exactly what part is borked.

 

[billcu]

I think the lower door needs to be in the up position when heat is selected?

Edit: Wrong, the lower door needs to be in the down position for heat

 

[Mad1stGen]

It sounds like normal blend door operation to me. The lower door has to be fully shut to get full heat. As Bill pointed out, the weight of the door will drop it down, and feel like a spring loaded mechanism.

The black arm might have a slight crack in it that you're not seeing from the top. But if it's only the gray arm that's broken, you can easily replace it without removing or pulling the dash at all.

 

[BlackIceLSC]

I am with you guys...I know I can swap out the broken arm. I'll try to clear up my description:

when I inspected the operation of the black arm, it is intact, no cracks, and no slippage on the axis. The actuator rotates the black arm as it should.

the metal rod was OFF both arms when I got the car. He handed it to me...it's in the glove box.

the gray arm has the curved retainer part broke off and the pin that the metal rod slides on to is also gone, but the gray "arm" is still there.

when I say "I pull down on the arm and rotate it towards the floor/glove box", it moves full travel, according to Bill's pictures and when I let go, it rotates back up from the weight of the door.

Here's my concern: with the climate control ON, and set to 90 degrees (full heat), the air is cold. With it ON at 90 degrees, when I rotate the gray arm to full travel (down) to get HEAT, the air temperature only increases slightly...definitely NOT HOT.

That's my concern...the gray arm DOES move the door. I CAN attach it with the rod if I replace the arm but what concerns me is even if it was attached, and connected to the black arm, there still is not FULL HEAT.
So it seems although I do have a broken gray arm, and the two arms are not connected, even if I replace the gray arm and connect the two, I am wondering why there still wont be HOT AIR coming in?

Perhaps an explanation as to which arm does what?
Does the black arm actually switch the TEMPERATURE from COLD to HOT? Maybe, although the black arm is rotating fully if it is stripped then perhaps it isn't going to full HOT?
(not sure which of the two arms actually controls the air temperature, the black or the gray)

thanks for all your input guys...I don't mind working on this baby, just don't ant to go swapping out parts that wont fix it.

Lastly, any suggestions how I can get the door to stay UP *if* I do somehow figure out how to get the system to blow heat?

 

[soclose]

Hopefully it's not what I'm dealing with. No heat so I thought it was the blend door. Not so lucky-it's a broken door on the heater box. So, Carlos to the rescue and looking forward to getting everything replaced (heater core & blend door) when heater box gets replaced. Then, MAYBE, the dash will not have to come out again.

 

[billcu]

Someone once posted a drawing or picture that showed the action of the 2 doors. The heater core is in the middle of the 2 doors, and they work together for the heat. I can't seem to find that pic.

Is it possible your thermostat is stuck not allowing the car to warm up properly? Maybe feel the hoses above and below the thermostat to make sure they are both hot?

 

[billcu]

I found the drawings, in a great post by Mark:

http://www.lincolnsofdistinction.or...php?35012-blend-door-actuator-Revisited/page5

 

[BlackIceLSC]

awesome!!!! thank you Bill!!!

I read the threads linked, stared at all the drawings and photos and read the text....answered so many questions for me.

I have one more question though:

what if the car thinks it's 110 degrees inside and it's only 55?
will the EATC *always* go to FULL HOT if you select 90 degrees on it, regardless if inside temps?

perhaps my ambient temp sensor is faulty, thus not allowing the black arm to close all the way?

I watched my black arm full sweep and it does hit the stop when I select full hot. I then reach under the dash and pull the gray arm down to close the lower door fully, yet luke-warm air is all I get.

puzzled, to say the least...

 

[billcu]

If you are sure that the doors are fully open to the heater core and seated where they should be for full heat, and your thermostat and coolant level is ok, you might want to check the temperature of both heater hoses in the engine compartment.

My brother's S10 had no heat, it took a flush of the heater core to get it flowing again. It's a common problem with those, but I never heard it happen to a Mark VIII.

 

[BlackIceLSC]

t-stat and coolant level are fine, full, and clear-flowing.
I suspect it to be HVAC or ambient temp sensor-related.

 

[BlackIceLSC]

UPDATE
so today I took the glove box down and the message center and screen out(testing my luck with not breaking things as I remove things AGAIN)

CONFIRMED:
black arm IS not broken, has been reinforced and is doing what it should
metal rod NOT connected to gray arm
gray arm has a broken tip
both heater hoses are warm/hot and coolant level is full and flushed

I watched the black arm do AS IT SHOULD when I change the temperature
I manually move the gray arm to its full travel and put a good load on it to ensure the door is CLOSED.

the air temperature does not get warmer than ambient.
when I select MAX A/C the black arm moved clockwise to extent and air is frigid cold
when I select 90 degrees, the black arm goes counter clockwise to its maximum extent. I manually pull the gray arm WITH FULL CLOSURE and still get no heat.


I am lost now.

I have gloves....that's all I know

 

[driller]

If the doors are functioning and there is still no heat, then the heater core must be plugged(inside) or blocked(outside)?

The only thing to do from here in my opinion is to investigate the heater core. You could remove it and replace it (which is what I would do if I went through the trouble of removing it) or you could disconnect the heater hoses and try to flush it.

 

[chris2523]

seeing as you are in Cali, the previous owner may have bypassed a leaking heater core.

 

[tixer]

Another thought. my '86 Town Car had a valve in the inlet line to the heater core that would allow the car to stop the flow of coolant in that direction while running the A/C. Eventually, that valve failed and I replaced it with an open brass fitting. Worked great.

Do our Marks have something similar? I've never even looked. But I'd think that the lines to the heater core shouldn't be "warm," but rather "Hot.." I agree with the others that there's a "lack of flow" for one reason or another..

 

[BlackIceLSC]

Heater core has not been bypassed, and by "warm", I meant "at proper operating temperature.
Coolant flows through the cross-over as pretty much all other Mark VIII's I've owned/worked on.
Engine temperature is correct, and I see absolutely NO evidence that the heater core has been leaking, or has been bypassed.

I suppose it could be plugged, but I am inclined to doubt it. This car is so immaculate, I suspect nothing but proper care and maintenance its whole life.
Previous owner only disclosed that the heater did work, then one day the gray arm broke and he gave me the metal rod that was left hanging off the black arm when it did.

 

[tixer]

Hmm....

mouse nest in the ductwork?

This is me, grasping at straws..

 

[BlackIceLSC]

My other thought is this:
the black arm is rotating, but the shaft it attaches to that goes through the HVAC box is broken, so in turn, the black arm, while rotating properly, is not closing the door inside the box.

Is this plausible?

 

[driller]

My other thought is this:
the black arm is rotating, but the shaft it attaches to that goes through the HVAC box is broken, so in turn, the black arm, while rotating properly, is not closing the door inside the box.

Is this plausible?

Plausible.