North American Turbocoupe Organization



inconsistant HVAC heat?...
Kuch Offline
Member
#1
My 88 TC has the EATC and I usually just select the temp and which vent to use, but as the temps are now colder I notice some strange happenings. If I set the temp to like 75 and put it to heat or defrost or where ever, the temp blowing out is pretty cold. The hot air will not blow out till I turn the temp up to 90, then it's nice a toasty. now I know how the regular controls work, with use of cables to move a blend door and such, but is our EATC the same? It is vacuum controlled, so maybe a bad vac line going to the blend door? Figured I would ask here before tearing into it. Thanks for any ideas.
1988 Turbo Coupe, Black/Black, 5 Speed, Moonroof, T3/T4 50 trim, 255LPH, BBK AFPR, 3" DP dual 2.5", MGW shifter, K&N, Gillis valve, RR cam
1964 Ford Galaxie 500XL, 390 6V, 4 Speed, Vast and fast
1960 Ford Starliner, 292 Y Block, 3 Speed, slow and low
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anasazi4st Offline
Senior Member
#2
Is it a continual or one-time thing?

Last week for no apparent reason the EATC just decided it was going to shut down. There was no apparent reason—quite the opposite. It was in the high 80s outside, and I had just gotten into the car after it sat for a bit in the sun, so it was a little warm inside.

If anything, the blower should have come on full blast. The temp was set at 74...but instead it just shut down. I manually turned on the A/C (fans on Medium, setting on A/C from Auto), the blower started up and worked just fine. After a bit I went back to Auto and it picked right up as if nothing had happened.

Over the years I’ve had this happen more than a few times. Before the last time I changed the heater core (2010) it happened frequently. In the process of doing that repair I also combed out the fins in the evaporator and condenser and sprayed some brake cleaner on a few of the sensors in the housing. Whether or not that affected anything, the problem (mostly) went away; last week’s incident was the first I can recall in quite a while.

You probably know that for maximum cooling you turn the temp to 60. No matter what the actual ambient air temperature is, you’l get full cooling. (This is the setting you use when you are recharging the a/c.) Conversely, if you set it at 90 you’ll get full heat (this is the setting you’d use when flushing the cooling system).

If anything, I’d blame the EATC computer and not the vacuum lines. Bottom line: I would not consider it to be a real issue requiring examination unless it happens either on a regular basis or all the time.
Another proud dues-paying member.

1987 Turbo Coupe w/T5OD, 8.8 axle, grey smoke; most options. Got it in 1991 with 41K miles: 3 turbos, 2 heater cores, 1 T5OD full rebuild, 5 clutches, 1 head gasket, 2 Teves II ABS units, etc. later....
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firebirdparts Offline
Junior Member
#3
They key to 90 and 60 is that no automatic temperature control is used on those settings. If the only way you can control temperature is 60 and 90, your problem is on the automatic side. I have had a Lincoln Mark VII for 30 years, so I am a little more familiar with that shop manual - They did a good job in the manual including resistance maps for the thermistors used to measure temperature.

Temperature measurement is the most basic thing to verify. If it can't measure temperature, then it can't do automatic temperature control. If something is wrong in its brain, then I would never be able to fix that.

The Mark VII's didn't use any vacuum, just stepper motors. I never really looked at the t-bird system (and mine doesn't have it) but I assumed it was the same.
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anasazi4st Offline
Senior Member
#4
Kuch, I found this for you—more information to answer your question.

Page 36-75-46 of Ford’s Chassis Electrical Shop Manual (Part I of II Volume B) describes a Self-Test for the EATC System:

“The control head will detect some system faults occurring during normal operation and has the ability to test for other faults during the Self-Test. If an actuator fault is detected by the control head during normal operation the VFD or mode LED will blink....To display the error codes for the fault detected, initiate Self-Test by pushing OFF/AUTO and DEFROST simultaneously and then A/C within 2 seconds....Error codes for any faults found during the Self-Test will appear along with any error codes for any faults found during normal operation. The Self-Test can be initiated at any time with the resulting error codes being displayed. Normal operation of the system stops when Self-Test is activated. To exit Self-Test and restart the system, push the COOL button.”

There is much more (22 pages) of tests for the various actuator motors, control head, etc. I believe Pete D. can email those pages of the manual (if you don’t have them); or I can photograph them and do the same.

Acciording to the manual, the Control Head is simply the EATC module just above the System Sentry unit on the Dashboard Center Console. This is the panel that features the temperature setting as an LED, with 9 push buttons to control temperature, fan speed, and manual operation and 7 LEDs to indicate the function selection.

firebirdparts Wrote:Temperature measurement is the most basic thing to verify. If it can't measure temperature, then it can't do automatic temperature control. If something is wrong in its brain, then I would never be able to fix that.

Agree with Joe. You’d fix it though by simply replacing the Control Assembly (or “brain”)—if that was the problem. There could be other things at play: the input(s) from the In-Car Sensor, Ambient Sensor, Engine Temp sensor could be a few possible reasons for the fault, depending on what the Self-Test tells you.
Another proud dues-paying member.

1987 Turbo Coupe w/T5OD, 8.8 axle, grey smoke; most options. Got it in 1991 with 41K miles: 3 turbos, 2 heater cores, 1 T5OD full rebuild, 5 clutches, 1 head gasket, 2 Teves II ABS units, etc. later....
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Kuch Offline
Member
#5
Awesome, thank you for the replies. Looks like a swap of the control in the dash will be able to tell me if that's it. Will scrounge the junkyards for one in the future. Also will try the fault test and see what comes up. At least I still have some semblance of control on it for now. I drove in to work tonight and it was 38 degrees outside, but the engine sure likes the cold air!
1988 Turbo Coupe, Black/Black, 5 Speed, Moonroof, T3/T4 50 trim, 255LPH, BBK AFPR, 3" DP dual 2.5", MGW shifter, K&N, Gillis valve, RR cam
1964 Ford Galaxie 500XL, 390 6V, 4 Speed, Vast and fast
1960 Ford Starliner, 292 Y Block, 3 Speed, slow and low
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anasazi4st Offline
Senior Member
#6
I appreciate your desire to scrounge around for one in a salvage yard or online (I’ve seen several on eBay recently)...but once again I’d suggest that, before you spend a lot of time, be certain that’s what you really need—do the tests. If this was 20 years ago and you could find a Control Unit just about anywhere, then yes go for it. But you could spend hours and $$ searching for and buying a part you might not need,

What if you go to that trouble, get another one and install it and it still acts the same way?

I’m a big fan of the Scientific Method, which has you do all the tests on something before you reach a conclusion. What if you get the result you want on the second test? The Method says you still go on and perform all the rest of the tests, maybe there will be another result you can learn from later on.
Another proud dues-paying member.

1987 Turbo Coupe w/T5OD, 8.8 axle, grey smoke; most options. Got it in 1991 with 41K miles: 3 turbos, 2 heater cores, 1 T5OD full rebuild, 5 clutches, 1 head gasket, 2 Teves II ABS units, etc. later....
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50RACER Offline
Senior Member
#7
Kuch Wrote:Awesome, thank you for the replies. Looks like a swap of the control in the dash will be able to tell me if that's it. Will scrounge the junkyards for one in the future. Also will try the fault test and see what comes up. At least I still have some semblance of control on it for now. I drove in to work tonight and it was 38 degrees outside, but the engine sure likes the cold air!


If you find that you need another EATC control unit, I have several and can ship you one for $45.
87 TC Medium Canyon Red
88 TC Black Beauty
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Kuch Offline
Member
#8
Thanks 50Racer, will keep you in mind if the local yards turn up nothing
1988 Turbo Coupe, Black/Black, 5 Speed, Moonroof, T3/T4 50 trim, 255LPH, BBK AFPR, 3" DP dual 2.5", MGW shifter, K&N, Gillis valve, RR cam
1964 Ford Galaxie 500XL, 390 6V, 4 Speed, Vast and fast
1960 Ford Starliner, 292 Y Block, 3 Speed, slow and low
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