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tedallen
09-01-2008, 10:04 AM
Hello,

I started having problems with my battery a couple of weeks ago (actually had to be jump started once). I eventually got Advance Auto to agree that the battery was defective and got it replaced.

Now my auto climate control is not functioning properly. Regardless of the temperature setting, other than the Off, Floor, and Panel settings, the A/C compressor is always engaged and the system is outputting cold air. Can't get heat in any setting. Even in Floor or Panel modes the temperature controls don't have any effect on the output temperature.

I tried to utilize the diagnostic steps at the http://www.sccoa.com/articles/climatecontrol.php link, however, my 94 has a rotary switch to change between Floor, Panel, Defrost, A/C, etc. modes as opposed to buttons. It also has a rotary switch for blower speed instead of a slider as the previously mentioned Automatic Climate Control self-test referernces. I did try setting the mode to Floor and the blower speed to high and pressing the "warm" and "cool" buttons simultaneously for 3 seconds, but I was never able to get it to enter diagnostic mode. I tried various other combinations of settings without success.

Here is how the system behaves in each mode:


Floor: A/C Compressor not engaged - Temperature settings don't change output temperature only blower speed if in auto blower position
Panel: A/C Compressor not engaged - Temperature settings don't change output temperature only blower speed if in auto blower position
Panel/Floor: A/C Compressor always engaged - Temperature settings don't change output temperature only blower speed if in auto blower position
Floor/Defrost: A/C Compressor always engaged - Temperature settings don't change output temperature only blower speed if in auto blower position
Defrost: A/C Compressor always engaged - Temperature settings don't change output temperature only blower speed if in auto blower position
A/C and Max A/C: A/C Compressor always engaged - Temperature settings don't change output temperature only blower speed if in auto blower position


Please note that in automatic blower mode, between 70*F - 76*F, the blower always operates at the lowest speed, regardless of the actual interior temperature relative to the preset setting. As the preset is increased from 76 toward 90*F, the blower speed gradually increases and reaches its maximum blower speed at 85*F and maintains it at 90*F. As the preset is decreased from 70*F toward 60*F, the blower speed gradually increases and reaches its maximum at 60*F. Again, the blower speed continuously increases regardless of the actual interior temperature relative to the changes in the preset value.

I am suspicious that a surge of some sort may have damaged caused a component to fail at some point after being jump started and/or when the battery was acting up and all gauges were acting strange on the day it died.

If anyone has any ideas on how I might be able to run a diagnostic or as to what the problem might be I would greatly appreciate any input.

It almost acts like the interior temperature sensor is being ignored. If it was always supplying a reading indicating that the interior was extremely hot, that would explain why most modes always put out cold air with A/C compressor engaged even if it is already cold inside, however, it wouldn't explain the dip in blower speed as the temperature preset is dropped from 90*F into the 70*F - 76*F range and then increase in blower speed again as the preset is dropped further below 70*F.

scbird1
09-03-2008, 09:50 AM
It sounds like the unit itself has failed. Try this first. Set the blower speed to its slowest setting and not auto. Try changing from floor to, ac ,def slowly and listen for the hiss and the door inside the heater box to move. If all you hear is a hiss then you have some vac lines off. Its its all working then you might start to look for a replacment on ebay or someone that is parting a 94 to 97 thunderbird SC or LX will work. These kind of problems can be a nightmare to figure out but look for the easy fix first like loose wires or something that might have got unplugged. Even a piched vac line will cause problems.

the-big-e
09-03-2008, 03:47 PM
I have a control unit that I just took out of my 95 SC.....

It's here if you should need it or any other part of the system.....

tedallen
09-28-2008, 10:40 AM
A Ford tech was gracious enough to print me off a page showing how to perform a self test of the climate control system on a 1994 T-bird with automatic climate control and it calls out a "02" code. According to the sheet that is a blend door problem.

Apparently there are multiple doors, one (or more) that divert air between the various vents and one that mixes the hot and cold air.

Since air gets diverted correctly between the various vents as I switch the controls, I suspect my problem of always getting cold (or cool air in "Panel" position and the A/C compressor doesn't run) is because of an issue with the door that mixes the hot and cold air.

Has anyone had issues with this blend door before that could recommend how to access and check it? It looks like there may be an electrical motor that controls it (according to a part sheet Ford printed for me). Is it easily accessible or does the entire dash have to be pulled apart?

Are there any vacuum connections that come into the back of the head unit that might prevent the blend door from operating properly?

tedallen
09-28-2008, 01:53 PM
I pulled the automatic climate control unit out of the dash and all 3 electrical connectors and the vacuum connector (with several vacuum lines coming into it) were securely attached.

Does anyone know which vacuum line(s) coming into the unit should be source vacuum and which ones should be switched to depending on the position of the climate control settings?

Best Regards,

Ted Allen

tedallen
09-30-2008, 09:37 PM
Can anyone tell me how to go about accessing the motor that control the blend door that controls the mixing of hot and cold air to maintain preset temperature with on a '94 T-Bird with automatic climate control? As mentioned in prior posts, I never get any hot air (i.e. it is stuck in the full cold position) and the self test calls out an "02" (blend door problem). I don't know if this particular blend door/motor combination is electrical and/or vacuum controlled.

If it is electrical, does it have a fusible link or is it protected via a fuse?

Best Regards,

Ted Allen

KMT
09-30-2008, 10:07 PM
Looks to be vacuum (RockAuto: 1994 FORD THUNDERBIRD SC 3.8L 232cid V6 MFI Supercharged (R) : Heat & Air Conditioning : A/C Vacuum Control Valve/Defrost door motor // MOTORCRAFT Part # YH529 {#F2UZ18A318B}) - location usually on the heater core box. Drop the glove box and take a close look at the top left...just my guess that is where it is mounted, sorry if it doesn't pan out.

Grab a vacuum test pump and start testing the lines on the back of the control module if you haven't already.

http://info.rockauto.com/getimage/getimage.php?imagekey=380572&imageurl=http%3A//info.rockauto.com/Motorcraft/YH529.jpg