91 LTC Sig ATC High Fan SPD Only

Tiny
TNC
  • MEMBER
  • 1991 LINCOLN TOWN CAR
To a Lincoln tech,

87,000 miles/car is driven only 500 miles on avg per year

How could I test the blower speed control module? With the module off the car is the resistor in/or on the module accessable so it can be be solder repaired with high temp solder?

What else does that module control, or does it only control the blower motor speed?

Can the module be bypassed so that the fan will still work on high, after I take it off to inspect/try to repair it/or replace it, etc and how could I do that, with some improv, but safe wiring?

I found a site that lists alot of used auto parts yards that have these; used speed control modules, for less than $75, but how can I be sure that they are ok, or that they will last (keep working)?

What other Ford cars and range of years and LTC range of years are the modules all the same,
so I can pick a used one from a later model car with less mileage?

Can you recommend a certain year Ford car or LTC that the modules were made better?

Recently, the blower motor started to only work on
the very high setting on the ATC vertical slide
variable speed switch.

Also with the car just started the ATC setting at the
bottom Auto position on the vertical moving variable speed switch does not get the fan to go on at all, with the temp control selector in any of it's settings.

After the heat is let to run a short time by setting the variable speed switch to manual high speed,
(which is the only fan speed that works) with the temp control set to 75 or more,

only then will the ATC Auto setting respond, but only if the temp control setting is set at 70 or below only.

There is no low, med, or med/high fan. No response, just silence.

How can I do some kind of basic or not so basic test to check if the part that needs repair or replacing is either the ATC Control Switch itself located on the dash, or the Speed Control Module located under the hood?

Floor vent setting has no response at all (no fan), but def/floor works fine, full flow at both vents???

The floor vent setting has not worked for a long time or has never worked (no response, silence) since I've had the car 3 years, but the max ac, ac, vent, def/floor, and def all work good.

Does that mean that the A/C/Heat Control switch itself has a short at the floor vent setting? Can that part of the switch be solder repaired, with the whole switch out of the dash?

This car has the Automatic Climate Control System/non digital display. It has a verticle moving variable speed switch.

At the very top position it goes on very high, and at the very bottom the switch clicks into the Auto Temp Mode.

At an auto parts site it says that if the 91 LTC has the ATC system then the alternate part instead of a standard delimiter type resistor is this part:

Heater Control Valve
VALVE, HTR WAT TEMPERATURE SENSING / LOCKOUT, ATC -Located in heater hose

What does the heater control valve do, and does it need to be checked for any of the problems mentioned above?

I did find one forum question that mentioned the ATC system and the blower motor speeds for this car. It was about the ATC and the A/C system not working as good as it should.

While responding to the question it was mentioned that when the blower motor goes on high, it has/uses its own seperate ground wire and the module has a relay for this.

Sometimes a problem with the other speeds could be related to the seperate ground wiring, for those other speeds and not to a faulty part.

Or the problem is the blower motor speed control module itself.

One of the forums mentioned that they sometimes have to be fixed or replaced because of solder problems with those units.

What is your diagnosis and/or suggestion on how
to test and fix the low-med/high blower speeds and the floor vent setting having no response (fan shuts off at this setting)?

Where/how do I check for proper ground for the different speeds that involve the speed control module.

There's alot of harnesses, wires and locations.
Which harness/location/what color wires will I be
checking/testing?

How/where do I check about the grounds?

I have a digital multimeter.

To test for ground the ohm meter is used to check for minimal resistance on full high speed, right?

I've never checked the fuses in this car, which ones should I check?

Side note: With engine running the lights inside the car are flickering and upon acceleration the flickering is not interupted that much it continues even with acceleration. What causes that?

With engine off the lights don't flicker at all.

What causes that?
Is that ok or is there something I can check/fix?

What does the Heater Control Valve located in the heater hose do as part of the ATC system?

How do I test this part? It is partly visible at the heater hose, right?

There is one more part to mention that I read about and that's the air temperature sensor (not the coolant temp sensor). Is that involved here in any way?

I read this on a forum

A common problem with the speed controller is that the master resistor that slows down the blower gets very hot, and melts the solder that holds it to the controller circuit board. In most cases, a higher temp solder fixes the problem.

I met a guy that had to replace a defective resistor too... He didn't want to put out the $160+ for the Speed Controller, so instead he found a supplier of just the resistor and made it work, that was two years back and still working.



The more reply the better, I want to do all of this testing and repair work on this part of the car myself even if I have to take apart the dash to test/fix the vent setting or the ATC part of the heater controll asembly.

Thanks


http://www.2carpros.com/forum/automotive_pictures/405478_lincoln_town_car_parts_1.jpg




http://www.2carpros.com/forum/automotive_pictures/405478_ltcairflow_1.jpg

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Friday, November 6th, 2009 AT 10:23 PM

7 Replies

Tiny
TNC
  • MEMBER
Waiting for a reply

Thanks,
Eric
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Tuesday, November 10th, 2009 AT 4:25 PM
Tiny
MERLIN2021
  • EXPERT
Test VBC like this, Blower On High Speed In All Switch Positions 1. Disconnect VBC connector in engine compartment. Turn ignition switch to ON position. Set controls to MAX A/C, medium blower speed. Using voltmeter, check for at least 10 volts between connector terminals No. 3 and No. 5 while changing blower speeds. If voltage is not as specified, go to next step. If voltage is as specified, check and repair wiring harness. 2. Disconnect terminal No. 2 from VBC connector and reconnect connector to VBC. Turn blower switch to low speed position. If blower is off (no voltage at blower motor), check and repair wiring harness. If blower is operating at high speed, replace VBC. you have no resistor because you have ATC system, flickering lights are usually caused by vlotage regulator on the back of the alternator, it can be changed without replacing the hole alternator, but getting the brushes in requires patience and two needles to hold them in place, also check battery cables.


http://www.2carpros.com/forum/automotive_pictures/62217_91TCBMSC_1.jpg

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Tuesday, November 10th, 2009 AT 6:21 PM
Tiny
TNC
  • MEMBER
Thanks for the reply,

[Test VBC like this, Blower On High Speed In All Switch Positions]

Did you mean do all testing starting in the high speed setting and then switching to the other speeds?

Because the blower is not running on high in all switch positions:

There is no response from the blower motor when the vertical moving ATC speed switch is any of the variable speed settings between auto and full high (low - med/high has no response at all).

Only full high works in the full high setting. If you slide the switch down just under the full speed setting, the blower motor shuts right off and does not work until you go all the way down to the Auto setting, and the fan only works on high in Auto, no other speeds.

But the Auto setting will only get the fan to work if the temperature control is set to 70 or below, and also after the heat has been on for a few minutes in the manual full high speed position, which is the only speed position that works. If you go above 70 temp setting in Auto, the fan shuts right off every time.

IF you start the car and don't turn the heat on for a few minutes first with the speed switch on the manual full high setting at around 75 temp setting, then the Auto setting will not turn the fan on at all (no response), even with the temp control set at 70 or less.

You have to use the heater for a few minutes on 75 or more 1st or the Auto setting has no response.
Auto only works when the temp setting is at or below 70.

If you start the car and put the ATC switch on Auto right away, it will not turn on the fan motor even after the car has been running a long time.

If you turn the fan on high with the temp setting at 75 or more for a few minutes and then go to Auto, then Auto will work, but only on high fan and
only if the temp setting is at 70 or below.

I found the heat control valve as soon as I looked for it. It's right on top of the VBS. How does that part work/interact with the ATC, temp selector control, and the VBS?

Does all of this tell you what's most likely wrong even without the tests you asked me to do?

What about the ATC switch itself, could their be something wrong with the variable speed switch, or not likely?

The only vent setting that doesn't work is the floor vent (the fan motor shuts off at this setting), but def/floor works fine. Can that part of the switch be repaired? What's wrong with it?

Does it hurt the car in any way if it's the regulator causing the flickering? Is it ok to leave it that way?
What will happen next? Are any other parts hurt by that flickering in the eletrical system?

The alternator has less than 1500 miles on it. They didn't change the regulator at that time, unless the regulator was part of the rebuilt alternator they installed.

What's more likely causing the flickering the regulator or the battery cables?

You want me to check the ground to the chassis and the alternator to the battery connections, right?

The battery was put in the same time as the alternator.

Thanks
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Wednesday, November 11th, 2009 AT 8:05 AM
Tiny
MERLIN2021
  • EXPERT
I found the heat control valve as soon as I looked for it. It's right on top of the VBS. How does that part work/interact with the ATC, temp selector control, and the VBS?
It shuts off the flow of hot hater to the core when an A/C temperature is selected. Your problem witht hte fan is 99.9 the blower motor speed controller.
Flicker, can be either, so clean BOTH ends of the cables especially the ground cable, the attaching point on the engine block sould be cleaned so both the cable end and the block are shinny. If flicker still persists, it would be the alternator/regulator, which does come with a rebuilt alternator, did the flickering start after the alt was changed?
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Wednesday, November 11th, 2009 AT 12:36 PM
Tiny
TNC
  • MEMBER
I'm not sure when the flickering started, it's just that now that I'm working on the cars electric that I really noticed it as maybe not being a good thing.

Also this is the 1st time that I ever tested it by accelerating and checking if the flicker would go away.

If a new voltage regulator was part of the new alternator than why do you ask if the flickering started after the alternator was installed?

If both were new than why would they be the cause of the flickering after they were both installed together, new?

Are you saying that the new alternator may not have been checked right or its belt tightened right, or etc, etc after it was installed?

Can you answer that so if it's not the battery cables, then I'll check and repair the alternator/ voltage regulator as you say.

I will clean the battery cables just as you said to.

What about the floor vent setting, it shuts down the fan, but def/floor works fine and so do all of the vent settings.

If I take the dash apart to get at the vent settings control can the floor vent setting be cleaned or repaired.

How do I get the floor vent setting to work?

Def/floor is only good when that setting is needed.
You can't close the def dash vents if its on def/floor.

The floor setting would be used as much or more than the panel vent setting.

It's too bad that these cars don't have a vent/floor setting.

I found a used auto parts site, I'm sure you've heard of it, that has used VBC modules for every kind of Ford car that uses them, and alot of them to choose from for each model and year and ranging in price from $30 - $100.

Most of them are listed as Condition A: under 200k miles, and 15k or less on avg per year. Even the lower price ones are listed as Condition: A

They list parts yards from all over the US. So the module can be ordered by calling a parts yard from any location in the US!

Would the module be in better condition from a location where cars use A/C mostly or from an area that used the heat and A/C equally, or it doesn't matter?

Is there a year of Ford car that uses the same module as the 91 LTC, where the modules were made better, or that tend to hold up better?

Is there a model or year to not get that model or years moidule?

Should I get a module from a later year LTC or other Ford car?

I'm not sure if they test them or if for example at $30-$50 they may say when I call them up, that they don't test them.

Afte4r you advise me about the module I'll decide which of the yards to call and see what they say about the condition of the used modulkes they have for sale.

Thanks
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Wednesday, November 11th, 2009 AT 8:38 PM
Tiny
TNC
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Waiting For Reply
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Friday, November 13th, 2009 AT 11:58 AM
Tiny
MERLIN2021
  • EXPERT
Sorry for the delay, but this is my part time gig, my money making job sometimes requires overtime as it did for the last few days, I did say it's 99.9% likly to be the blower motor speed controller, and if it was a car I intended to keep, I would get a NEW one, not a junkyard electrical part! That's why I would also TEST it before replacing it! Here is the COMPLETE section on your auto temp unit: Actually check your email, it's detailed and goes into specific function testing, the floor air problem could be the thermal blower lockout, this will tell you what and how, good luck, and let us know how you do!
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Saturday, November 14th, 2009 AT 6:54 AM

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