94 SC Climate Control Issues - No Heat

I spent several hours today trying to troubleshoot a "no heat" condition in the subject vehicle.

A self-test run on the automatic climate control unit called out a code for a blend door issue which would make sense.

I removed the head unit from dash and disconnected the vacuum connector (6 port connector but only 5 of them are active, with the 6th port in the connector being sealed). I confirmed the vacuum lines are all holding vacuum and they are colored as follows:

Black - Supply vacuum, presumably coming from off of the tee
on the passenger firewall next to where the A/C lines come
through the firewall to the evaporator.

White
Red
Yellow - When vacuum is applied to this line all air output is diverted to
the panel vents.
Blue

I couldn't tell exactly what was happening when I applied vacuum to the White, Red, and Blue lines in the connector but they all held a vacuum. At this point, I'm thinking the problem is not vacuum related.

I then started evaluating the electrical connectors on the back of the unit. There are 3 of them, 1 red connector (4-pin next to the vacuum connector), 1 grey connector (13-pin only 10 pins used), and one black connector (13-pin only 10 pins used).

I did do some testing of the 4 wires coming into the red connector adjacent to the vacuum block (behind the rotary dial to control air distribution to the panel, defrost, floor, ac, etc.):

Rotary Switch Position
Max AC AC Panel Off Panel/Floor Floor Floor/Def Defrost
Wire
W/LtBU 12v 12v 12v 12v 12v 12v 12v 12v
PU 12v 12v 12v 12v 12v
BR 12v 12v 12v 12v 12v 12v 12v
PU/O 12v 12v 12v 12v 12v 12v 12v 12v

Where W/LtBU = White/Light Blue, PU = Purple, BR = Brown, and PU/O = Purple/Orange for the wire colors.

The wiring schematics for 94-97 T-Birds in my Haynes manual show climate control wiring, but it does not appear to be correct for the automatic climate control vehicles.

I dropped down the glove box and could not see any signs of a blend door (or associated motor) behind it for controlling mix of hot air across the heater core with outside and/or A/C cooled air.

From the location where the heater hoses enter the firewall, I suspect the heater core is almost directly behind the center of the dash, which I can not see much of at all even with the glovebox dropped down and the climate control unit pulled out of the dash. I probably should pull the stereo head unit out as well and see if I can find anything behind it.

Has anyone else experienced this issue with a 94 or newer T-Bird with automatic climate control (mine has hot (red) and cold (blue) buttons and an outside temperature button, a lcd display of the temperature, a rotary dial for selecting max ac/ac/panel/off/panel-floor/floor/floor-defrost/defrost, and a rotary dial for selecting fan speed that also supports an "Auto" setting).

With the fan speed selector switch set to "Auto", as I manually change the temperature set point toward the low end (60 degrees) or the high end (90 degrees), the fan speed will inrease to the maximum regardless of what setting the max ac/ac/panel/panel-floor/floor/floor-defrost/defrost rotary selector is in. As I adjust the temperature set point back the opposite direction from the maximum hi or minimum low positions the fan speed will consistently decrease until around the low to mid 70s when it will begin increasing in speed again.

At this point I suspect the blend door motor is electrically controlled as opposed to being vacuum controlled.

I did find a door behind the glove box low back against the firewall that was hinged on the firewall edge and opened upwards from the floor, however, none of the controls seemed to change its position and even when I manually pushed the door upward to a different position it did not change the air temperature output from the vents. Based on its position I doubt that it would be used to control a blend of hot air from the heater core anyway with exterior or A/C cooled air anyway.

If anyone has photos of the heater core and ideally the blend door and its motor (or vacuum connections) I would greatly appreciate it. If anyone has experience with how to fix this issue that would be ideal.

Best Regards,

Ted

you are correct, the blend door is controlled by a small worm gear assembly. Its located right next to the heater core access panel. I have a good working one off of my 94, figured I'd save it for just the issue.

Rpdboss said:

you are correct, the blend door is controlled by a small worm gear assembly. Its located right next to the heater core access panel. I have a good working one off of my 94, figured I'd save it for just the issue.

Click to expand...

Hi Rpdboss,

I take it the blend door worm gear is driven by an electrical motor then? If so, is it typically the motor that fails or the gear on the blend door?

Where is the heater core access panel on a '94 SC? What portions of the dash need to be removed to gain access to it?

Did the behavior I described match with the symptoms you encountered when your blend door malfunctioned?

Thanks,

Ted

dash removal how to

I will have pics up of the heater/ac assembly as it can be removed as a whole by tomorrow. That way I can show the motor assembly and where the heater core access panel is.
When replacing the heater core the first time i was able to unbolt the dash as swing it back a bit allowing access from the passenger side. This time when I stripped the car of its parts I did it faster and smarter.

1:There is a trim strip that runs the length of the windshield, it has a photo sensor for both solar load (ac) and dusk sensor on it. Gently pry it up and disconnect the connector for said sensor. Remove whole strip and store safely

2: remove all the bolts the the strip revealed, 8mm. This hold the dash along the top to the firewall area.

3: on each side by the door hinge area just under the dash to the side you will encounter a stud with a nut on it, remove them, 3 total I believe. This holds the main support member inside the dash. 13 mm i believe. The second one on the drivers side is tucked up a bit and only allowed me to turn 5 degrees at at time

4:Remove the panel that's directly under the steering column to allow access to the more bolts. Along the steering shaft near the firewall you will spot a pinch collar with a bolt to hold it tight. Just loosen this one bolt, nothing else on the shaft. ( never tried leaving the steering column firmly attached to the dash just to replace the heater core but MAY be possible) I found it best to remove the air duct directly below the column to allow more access and for it to drop low enough fro removal .There are four nuts on studs closer to the steering wheel itself that need to be removed to allow the whole assembly to drop and clear these studs. Carefully remove/unplug and tight/short wire connections. Removing the whole steering assembly is your choice, there are more wire connections to remove and 2 torx screws that hold the auto shift lock cable. When removing the whole assembly hold it low and gently pull back, careful of any missed connectors.

5: Locate a L bracket on the drivers side close to the tranny tunnel that hold the the bottom of the dash to the front of the shifter console. remove both bolts. Remove the shifter console screws and move back enough to allow access to the lower dash. There you will find 3 screws along a plate that hold more of the dash to the car's body/shell. If the car is an auto there is also a trans wire harness to unplug.

6:On the passenger side of the car there are numerous wire harness connectors for various systems that are part of the dash. These need to be unplugged. The antenna one I have not found a connector for, there may be enough slack to allow room to swing the dash out, if not unplugging it from the rear of the radio may help. I cut this during dash removal.

7: Only for dash removal: There are two large wire harness connectors for the dash and the fuse panel. The one under the dash close to the fuse panel can be separated by removing the center nut and pulling apart. The other must be removed in 2 steps. The bolt holding the firewall connector must be undone from the exterior of the car next to the brake booster. When that is undone there are small tabs that must be squeezed in order for the connector to release from the firewall. Then there is the matter of the boost/vacuum line to the dash. there is a small connector that can be simply pulled apart when the dash is pulled back some to expose. Removal of the shifter assembly will help in full removal of the dash without removing the doors for better clearance.

8: Wiggle and pull the dash up and outward from solid points as not to destroy brittle plastic. This should allow the dash to come off it's mounts and come forward or to swing to one side. If things wont move much check for missed bolts or connections hindering removal. A second pair of hands is a great help.

This should allow you access to the heater/ac box assembly. I will get pics tomorrow of this.

Pic as prommised

A simple worm gear driven assembly to control the blend door.

Rpdboss said:

A simple worm gear driven assembly to control the blend door.

Click to expand...

Thanks. Is the component labeled "ATC" the electrical component that actually opens and closes the blend door?

If so, is it not accessible if that is all that is being replaced without removing the entire dash? My heater core isn't leaking, I just don't have any heat and the self test says there is a blend door issue.

Also, is there an in car temperature sensor that is supplying the interior temperature measurement to the automatic climate control unit so it can adjust the fan speed (when in auto position) and mix of hot and cold/ambient air (presumably via the blend door) to obtain the desired temperature set point? If so, do you know where it is located (possibly in one of the panel vents) and whether or not if it had failed if it could cause the blend door to always stay in the same position (i.e. no heat if the temperature sensor is supplying a value that would indicate a temperature hotter than the maximum temperature setting on the automatic climate control unit of 90 degrees)?

Thanks,

Ted

Yes the part itself is labeled ATC but the label is too faded for the camera to pics up on. Might, might be accessible if the glove compartment door is removed and some ducting is taken out.

When I took my dash apart the first time I found that there is a sensor behind the area indicated. Behind that was a ribbed tube leading back to the blower inlet. This I believe is also "t" 'd to the blower motor's case to help cool the windings.

P.S. not sure what tbird this 5 spd console came from, no fog or arc, no hand brake, no indicator lights or cig lighter...

Rpdboss said:

Yes the part itself is labeled ATC but the label is too faded for the camera to pics up on. Might, might be accessible if the glove compartment door is removed and some ducting is taken out.

When I took my dash apart the first time I found that there is a sensor behind the area indicated. Behind that was a ribbed tube leading back to the blower inlet. This I believe is also "t" 'd to the blower motor's case to help cool the windings.

P.S. not sure what tbird this 5 spd console came from, no fog or arc, no hand brake, no indicator lights or cig lighter...

Click to expand...

My dash has the same slotted slightly raised area on it as well. It would make sense that there was something behind it. Furthermore it would be a good spot to get a reading of air from within the cabin about midway between the floor and roof. I wonder if anyone knows how to test it?

With the glove box dropped down I don't recall seeing anything except maybe the right-hand side of the black box enclosing the heater core. If that is the case, I would think the "ATC" blend door motor that drives the blend door would be located more toward the center of the car or maybe even a little left of center. If the amount of the vacuum line bundle hanging down over the front of the enclosure in your photo is about the length that would be available to reach the back of the automatic climate control unit in the dash, I would think the blend door motor couldn't be far from the control unit. I am wondering if it would be accessible through the front of the dash with both the climate control unit and radio removed? Is the part of the center console that wraps down around the transmission tunnel toward the firewall removable without removing the entire center console? I think I remember seeing a little round plug on it that I suspect hides a screw.

If you look at the oval hole on the firewall that is where the heatercore passes through. Based on this you can compare it the the pic of the heater/ac assembly and figure how far over the ATC control is. I'd say it is located right of the center of the car. If this does need replacing then just pulling/swing the dash on the passenger side may be your best option. I do recall a self test program that the auto climate control can run, how to access it I have forgotten

tedallen said:

the amount of the vacuum line bundle hanging down over the front of the enclosure in your photo is about the length that would be available to reach the back of the automatic climate control unit in the dash, I would think the blend door motor couldn't be far from the control unit.

Click to expand...

The vacuum lines you see are of the other end of the connection that goes to the dash unit. There is about an equal length on the dash side that plugs in to the ones you mention that go to the heater/ac box assembly. If it helps you any I can take a pic of the backside of the whole dash assembly.

Rpdboss said:

If you look at the oval hole on the firewall that is where the heatercore passes through. Based on this you can compare it the the pic of the heater/ac assembly and figure how far over the ATC control is. I'd say it is located right of the center of the car. If this does need replacing then just pulling/swing the dash on the passenger side may be your best option. I do recall a self test program that the auto climate control can run, how to access it I have forgotten

Click to expand...

A Ford Tech actually gave me the sequence of buttons you had to push in combination with dial settings on the auto climate control unit to get the self test to run. I can't seem to remember it now either, but when I did run it the code was for a blend door issue.

Rpdboss said:

The vacuum lines you see are of the other end of the connection that goes to the dash unit. There is about an equal length on the dash side that plugs in to the ones you mention that go to the heater/ac box assembly. If it helps you any I can take a pic of the backside of the whole dash assembly.

Click to expand...

I was hoping that the vacuum connector hanging down in your picture was actually the connector that attaches directly to the auto timperature control unit in the dash. If that were the case then it looked like the blend door motor couldn't be far from the ATC unit in the dash and I was hopeful I might be able to remove that unit, the stereo and possibly the black bezel that goes around them to gain access to the blend door motor.

Found Auto Climate Control Self Test

I found the self-test instructions today and ran them. The steps are as follows:

• Initiating Self Test (1994-1997 Thunderbird/Cougar)
  • Before the self test can be initiated, the Fan speed selector must be put in the "Auto" position and the AC/Panel/Defrost/Floor selector must be put in either the "Panel" or "Floor" positions. Additionally, the ignition switch must be in the "Run" position. To avoid false trouble codes, the self-test should only be run when air temperatures are in the 40-90 degrees Fahrenheit range (4.4-32.2 degrees Celsius).
  • Press the "Outside Temp" and "Cool" buttons simultaneously (actually I have found it easist to press one or the other of them and while it is depressed press the other and then release them both)
  • Within 2 seconds of releasing the "Outside Temp" and "Cool" buttons press the "Warm" button
  • The display should go blank and the blower motor should stop. If any trouble codes, either hard or intermittent are present, they will be displayed after 30 seconds or so.
• Terminating Self Test (1994-1997 Thunderbird/Cougar)
  • To terminate the self-test and save any stored codes, press the "Cool" button
  • To terminate the self-test and remove all trouble codes, press the "Outside Temp" button first, and then the "Warm" button (Note: I can't tell if this actually terminates the test and clears the codes or not)

After any corrective measures are taken, the self test should be run again and exited by pressing the "Outside Temp" button followed by the "Warm" button to clear any pre-existing codes or codes introduced during troubleshooting.

I can't find a list of all of the trouble codes, but mine is reporting 02. I can't remember if this is the one for blend door problem or not. I believe it is.

dash pics

Here is what the back of a 94 dash looks like. Not something the everyday SC owner gets or wants to see

In hopes that maybe my EATC control unit might be the "real" problem instead of actually being the blend door itself, I went to the local Pull-A-Part and bought one out of a '97 for under $15 warranty and all. I replaced my unit with it and it did behave a little differently.

The instructions to push "Outside Temp" and then "Warm" to exit the self-test and clear codes actually works with this unit (I think on my original '94 unit pressing the "Cold" button was actually clearing the codes based on the way the display acted as opposed to exiting and saving codes which is what the instructions say should happen). With the unit out of the '97, rather than the display staying blank while the self test is running, a counter-clockwise tracer runs around the outside border of a zero (0) on one of the digits in the display.

The '97 still exits with a trouble code, but it is a 24 instead of an 02. From what I can tell, both indicate a blend door issue, with 24 indicating a blend door actuator malfunction (some documentation I've found says intermittent, some says hard).

So, it looks like I'm going to have to try to get to the darn actuator. I can see part of it looking up from the passenger side footwell with the glovebox dropped down. However, there definitely isnt' clearance to get to it to remove/replace it.

I also introduced a new problem while testing. I no longer can pull a vacuum on the yellow vacuum line coming out of the back of the EATC unit. I found that the other end of the vacuum line is hanging down next to where the duct is that diverts air until the driver's side footwell on top of the transmission tunnel. I can't tell exactly where it should connect to, but from a photo I saw of the firewall side of the box that the heater core is installeed into, it looks like there is a vacuum driven motor at the upper-left (from the perspective of facing forwards in the vehicle) firewall side of the box. I don't know if I can fish my arm up through from the driver's side footwell and over the top of the box to try to reconnect it or not.

If I had room to get my car in the garage, I'd probably just go ahead and start tearing it apart.

I found the vacuum motor that the yellow vacuum line connects to yesterday and got it reconnected. I'm heading to Pull-a-Part today to see if I can get one of the dashes apart enough to get to a blend door motor.

I got a blend door acuator motor out of a '97 T-Bird at Pull-a-Part last weekend. It wasn't too bad of a job to get it out (thanks to several posts here and on tccoa regarding the subject). It didn't hurt that the seats, center console, kick panels and part of the dash panels had already been removed.

The one "hidden" stud behind the dash just above the transmission tunnel is a bit of a pain to get to. At least in the vehicle I was working with, there is an amplifier looking device clipped into a plastic tray which is part of the dash framing as best I can tell. That is just an inch or so above the tunnel and has a couple of wiring harnesses clipped into the bottom of it (with push pins) that make it almost impossible to get a deep-well socket on the nut without removing the amplifier from the tray and then pushing the connector push-pins back out of the bottom of the tray so the harnesses can be moved around.

As another post had mentioned, it appeared that the "yellow death" sealant had been used by Ford to secure the top of the dash to the firewall. I was doing the work by myself and never did really get it broken completely free at the top, however, I was able to tilt the dash up off of the studs enough to prop it up with an airbag assembly from the steering wheel I found lying around. I jammed it between the bottom side of the center of the dash and the top of the transmission tunnel and had enough room to access the blend motor actuator from underneath and also by reaching through the access holes where the stereo and automatic climate control control units had been removed.

Does anyone know of a way to test the blend door actuator motor while it is out of the vehicle? Also, any clue what voltage it operates at? I hate the thought of getting things put back together and finding out the one I pulled is bad as well. It has an 8-pin connector on it. If it was only 3-pins I could assume two were for power (forward/reverse) and one for ground. With all of the extra pins, I suppose some are for feedback to the control unit.

Best Regards,

Ted

ATC, where to get??

Does anyone know where to get a ATC unit that "rpdboss" is talking about? Is the EATC the same unit? Took mine ATC apart yesterday and there was grease all over so there was no contact, I cleaned it and put it togheter. But the best would be to replace it.

Thanks!

heater core HELP ?

Rpdboss said:

A simple worm gear driven assembly to control the blend door.

Click to expand...

can someone tell me is the small white arm in picture of POST 5 supposed to rotate when you move the heat control knobs on the dash? i replaced the heater core this week and after reassembly , i have airflow yet i don't have any heat just cold air. How is that ATC supposed to work?

TEDALLEN:

PM Sent

regards

Sean