no heat, need help quick...

[87_crown_vic]

ok...car is up to temperature. i unplugged and capped the vac line for the flapper door. i put a jumper on the lockout under th hood so that the floor settings work. all the blower settings work. STILL NO HEAT. i flipped the glovebox down and the housing around the heater core is warm. what is keeping the blower from blowing across the heater core??? is it completely open and something could be blocking it, or is there something that keeps the fan from blowing across it??? after i use the jumper wire, do i plug it back together under the hood? i noticed there is 2 vac lines running to that.


so what is keeping the damn fan from blowing across the heater core???

[Nathan in MI]

Have you checked to see whether there's power getting to the motor or not?

[87_crown_vic]

what motor? the fan is working fine at all settings...just seems like there is something not letting it blow across the heater core.

[Nathan in MI]

Oh, okay. I misunderstood. I thought you meant the blower wasn't working.

[87_crown_vic]

where is the ATC located??? is it the black looking relay under the dash/above & behind the glove box? if so i might snag it from Deuce

[gadget73]

The ATC isn't an electronic part, its a combination of a couple of vacuum parts. . The actual core parts are the interior temperature sensor above the glove box and the vacuum servo on the blend door under the dash. You disconnected vacuum to the blend door, so it should force it to hot. If its not going to hot, you'll need to pull the dash pad so you can see whats going on with that servo. Its connected to a crank rod thing that moves a flap back and forth. Either the vacuum can is disconnected from the crank, and it happens to be stuck set towards cold or the door is jammed towards cold. There honestly isn't much in there, and the vacuum ATC, while being a little finicky is overall mostly reliable. The blend doors seldom stick or break but it can happen. I'd bet its stuck and if you get your hand in there, you can free it up pretty easily. You should see whats going on if you pull the dash pad.

A bit of ATC operational theory might help. The mode selector diverts vacuum to 2 vacuum motors under the center of the dash, directly above the trans hump. These doors are the floor/defrost motor, and the dash vent on/off motor. All those do is direct air to the apropriate hole in/under the dashboard. No vacuum at all defaults to air coming out the defrost vents.

The temperature slider operates a cable that connects to the interior temperature sensor above the glove box. All this thing does is match vacuum to temperature, and the cable adjusts tension on a spring. Its essentially a rubber diaphragm with a piece of metal under it, and a spring attached to the middle of the piece of metal. The metal warps with temperature, and allows more or less vacuum to leak across the rubber diaphram from one port to the other. The spring in the middle has it's tension controlled by the temperature lever. More tension = more vacuum, and more vacuum forces the blend door servo to the cold position.

From the interior temp sensor, there is a vacuum hose that runs to the blend door servo in the main air plenum. This is attached to 2 parts, the flap inside the air plenum that selects air to be pulled through the AC evaporator or the heater core is the device thats actually responsible for temperature control. The other thing attached to this motor is the fan speed selector for the Auto position on the ATC head. The way that works is that as the temperature gets closer to where you want it, the blend door servo moves closer to center between heat and AC. As it approaches center, the contact on the fan controller moves, and slows down the fan. Its not critical to ATC function, and can be easily overridden by selecting a speed other than Auto on the fan speed selector.

The thermal blower lockout is located in the heater core feed hose. Its function is to not allow power to the blower motor when the mode selector is placed on floor mode until the coolant reaches 120 degrees. The vacuum portion of this switch ensures that the outside air door is closed when the engine is not warm enough to produce effective heat so that cold air wont trickle through the floor vents. It is only used in the Floor position, and you can override it by using any other position.

The last motor is the recirc door which is located nearest the passenger side kickpanel. This door is attached to the bottom of the fan box, and opens when the AC is in Max Cool mode so it pulls air from inside the car instead of fresh air from the outside.

Hopefully that will explain a bit about how that disaster works. Its honestly not that complicated when you get into fooling with it. Its maybe not quite as direct as a cable on the blend door but the basic logic isn't really that different. The only big change is that it uses a vacuum motor to move the blend door instead of a cable. The rest is basicly the same as a non-ATC car.

[87_crown_vic]

i must be missing one of the vacuum servos on the passenger side. all i see is the one that operates the recirculating flap. the door is shut. so there has to be something between the fan and the heater core. i pulled/dropped the glove box in Deuce and it looks totally different. i was guessing there was a door that wasnt opening to let the fan blow over the heater core. damn, now i have to pull the monster of a dash out to see what the hell is going on. the dash pad runs down the front to just above the glove box. glad i dont have to be to work till late tomorrow. i might have to drive it while its ripped apart.

[87_crown_vic]

is this the servo that you are talking about...
http://www.grandmarq.net/vb/attachme...9&d=1164435276
i saw this pic in a post. that servo must be way up in there. i will pullthe dash pad out and see why it is sticking from letting the heat in the car. i see what you aree talking about now that i have seen that picture.

[gadget73]

That is the temperature sensor.

You dont need to pull the whole dash out, just take the dash top off. The ATC system should be just about identical for all years of box as far as I know. The later electronic ones use an electric blend door servo, and those fail all the time. The can to disconnect is directly behind the glovebox door. Open it and its straight inside. Only one you can access from the glovebox opening with reasonable ease. You can probably look in there with a mirror but I find pulling the dash top to be pretty easy on most things I've worked on, and you do get a better view.

[87_crown_vic]

but that is the rod i need to move right? that opens up another flap doesnt it to let the air flow across the heater core? if you look at the pics of Zack's waggin interior pics, my dash is set up the same. the dash in the picture i showed you is like the dash in my 87s. i saw a relay behind the glove box and a black box with numerous wires plugged into it. i am gonna take the dash pad off like you said, or at least try to and see if i can find that rod and get it to open.

[gadget73]

This is an exploded (literally) view of my dash. Blue thing up top is the interior temp sensor. The white box is the heater core box. The wide dark stripe is actually the hole the core came out of. If you look off to the left of the hole, you'll see a rusty looking metal shield. That shield is over the blend door servo where it hooks to the blend door itself.


http://www.grandmarq.net/vb/attachme...8&d=1166325824

[gadget73]

That temperature sensor is just a calibrated vacuum leak. Trace the clear hose from it. The thing it connects to is the blend door servo. Thats the part that actually moves the door.

[87_crown_vic]

so it is the blend door that is probably jammed up and not opening right? i know that the fresh air door is closed, and all my other vents work. the blend door is what actually will let teh heat in??? i hope i get this because it is really getting frustrating driving w/ frost on the inside of the windows.

[gadget73]

Yes. The blend door switches the air from blowing through the heater core or blowing through the AC evaporator.

[87_crown_vic]

ok...here is what i found out. it warmed up a little bit the other day. my guess is that the previous owner had more water than anti-freeze. it had an ice chunk blocking the heater core or the radiator and it wasnt allowing it to flow right. when it warmed up, i checked the coolant and it dropped significantly due to the ice jam being gone. added 1 1/2 gallons of 50/50 mix and it has heat now. i noticed that the 90 and 91 set up is different also from the earlier box versions under the dash also. at any rate the problem is solved. thanx for your time and help. like i said, i think there was ice in the system that was making the fluid level look correct. after it had warmed up and i let let it set to check it it was significantly low.