How to: Fix broken blower speed control / compressor clutch

Discussion of STOCK TripMinder®, audio, video, LED, capacitors, instrument clusters and controls, integrated circuitry and boards, low voltage, message center, resistors, speedometers, tachometers, transistors and systems.

How to: Fix broken blower speed control / compressor clutch

Postby MKVII » Tue Jul 07, 2015 4:30 pm

Dear Mark VII enthusiasts,

Warning: Do this repair at your own risk or let it be done by a skilled electronic expert! No warranty. See original shop manual, chapter 36 (automatic temperature control) for servicing and self test of all related components of the automatic temperature control and blower speed controller.

This fix applies for 1984 Lincoln Mark VII, later models (1984 - 1987 or later) probably working in a similar manner.

Introduction

As my air condition started to fail months after refill, I checked the system for reason earlier.

Self test of compressor clutch "not engaged" yielded this condition: "REPLACE blower speed controller". All other components working properly. This condition shall be accompanied by a working clutch signal from the automatic temperature control (gray/white wire), with the blower motor properly working in all settings of the temperature control unit. The gray/white signal wire from the automatic temperature control to blower speed controller should have these voltages to ground:
- Position OFF and ECON shall yield about +12 V.
- Positions LO, AUTO, HI, MIX and defrost yield a signal closer to zero (+3V).

Quick test: the blower motor is fine, system refilled, pressure switch closed, the clutch working, if engaged with 12V, but not engaged by the automatic temperature control. Check continuity from compressor clutch output (green wire, see images) via pressure switch to compressor clutch connector.

How to fix by modernization of electronics

The automatic temperature control goes to the blower controller by a 6-wires connector behind the dash. The blower speed control has two primary funtions: engage compressor clutch, control speed of blower motor. The blower speed controller is located in the evaporator case, downstream of the evaporator core. The controller and connector can be accessed by opening the glove box and carefully pull the hinges to let it hang down (see picture of controller).

There are six wires going to the connector of the blower controller. We are interested in these (see images):
- white/purple: Power supply, +12 V, if ignition on, wire located on the bottom right of the connector.
- light green: Clutch power, +12V if clutch disengaged, wire located on the upper right of the connector.
- gray/white: Clutch signal wire from temperature control, +3 V if clutch engaged, 12V, if clutch disengaged, located on the middle, left.

These wires go to a power transistor in the blower speed control, that seems to be prone to overheating. I found many contributions complaining about this fact trying to fix with original replacement or swap of the power transistor. Therefore, repair "like original" is not a preferred solution. This is caused by the old designs of such transistors available at the time the car was built. This transistor can easily be replaced and modernized with a trouble free solution provided for your convenience.

The above voltage conditions of the clutch signal wire will simply allow to drive a modern p-channel power MOSFET switch, like the IRF4905 (Supplier: International Rectifier), which has low resistance and is capable to drive up to 70A. Don't worry, the power supply of the controller and clutch is secured by 20 A max (fuse No. 6). Advantage of this transistor type is a low heat sink required and no extensive cooling required. This is optimal to create a solution, that can be placed outside the air flow of the blower and hidden under console. There are two modifications, that one can think of: (1) modify the original blower speed control module by exchange of the original power transistor with the new type or (2) cut the wires to insert a new modern switch.

Option (1) comes with the disadvantages of tricky removal of the blower speed controller behind the glove box and required knowledge how to modify the circuit layout. I didn't check this possibility, because I was unable to get more informations about the circuit layout of the blower speed control using a contact at Ford (expert may help me out here to clarify). I also was unable to remove the module behind glove box without disassembling the whole dash. Therefore, I decided the removal of the original controller is close to impossible without huge effort and time.

Here I go with option (2) which requires less skills to cut certain wire, use a simple soldering iron, a bit of tape and special parts. Advantage of this solution is the possibility to roll back to original setup without irreversible modification of the car (if one decides to do so or go with option 1 later).

Parts required in addition from an electronics parts shop:
1x power MOSFET IRF4905
1x resistor 56k Ohm
1x heat sink for the transistor (>7 K/W)
1x small experimental box to create more security and stability for the new electronics
1x heat conductive paste (also available in computer parts store)

Note: Disconnect the car battery minus terminal before starting repair!

Open glove box and let it hang down. You should see this, left hand side behind glove box. The 6-wire connector of the blower speed control is more or less easily accessible behind glove box. The green wire (upper right) goes to the clutch. It is already cut in this image. Use tape to isolate the remaining piece of wire to the connector. The transistor drain goes here to connect to the wire to the clutch. Check continuity of this wire to pressure switch in engine compartment. The red signs on the blower control unit indicates, it has been fixed in the past and the part number was removed. This may indicate: it is broke at least for a second time due to overheating.
Image

Shown are the pins of the new power MOSFET. Pin sequence from left to right is G-D-S (G=gate, D=drain, S=source). A green wire will connect to clutch signal via resistor to "gate" of the MOSFET (left), the yellow wire soldered on "drain" (middle pin) and will go to the green signal shown in picture before, the red wire from "source" of the MOSFET will go to white/purple ignition (+12V) from the connector.
Image

Next picture shows a more secure isolation of the pins with heat shrink tube after soldering the wires and resistor. The power MOSFET will now be mounted onto a heat sink (black), that will later be screwed onto our small metal box (silver).
Image

Next picture shows the mounted box. Use heat-conductive paste between the transistor and heat sink (silver under transistor back side). Use a glimmer plate or plastic isolator plate to isolate transistor and heat sink from the metal box (not shown, hidden under heat sink). I added this "feature" to avoid short cut, if the box is accidentally placed where it could connect to chassis ground. The box is also securely taped with PVC tape, where it may connect to ground.
Image

Working with a soldering iron in a car I use aluminum foil (available in super market) to protect against brazing solder and heat from the soldering iron. Shown here are the cut wires of compressor clutch output (green) and the white/purple ignition wire. The latter ignition wire needs to be reconnected (soldered) before it is connected to the power MOSFET (see next picture). The aluminum foil will be removed after work, of course.
Image

Wires from the connector are now cut appropriately and connected to the transistor wires. Shown here is the special case of a Y-connection of the white/purple power line. This one needs to be still connected. Therefore, cut it, get it soldered again and connect the red wire to it. Then isolate with tape. This ensures the temperature control and blower motor will still work.
Image

If all wires are connected, the clutch should now be driven by the automatic temperature control bypassing the original blower speed control. Check if the air condition will work as expected. Carefully check, if the power transistor will heat - it should not heat up. Be very carefully, because if the MOSFET may fail (e.g. you may have accidentally exchanged pin layout), it can be extremely hot and may cause burn and injury! If it is working and remains "cool", then the repair is successful, the wires and new "controller" can be easily hidden between floor and console.
Image

Test the new unit

Double check wiring after soldering and before reconnecting battery.

After applying this fix, start the engine with temperature control in "Off" or "Econ". Check if the compressor clutch remains disengaged. Set the control to lowest possible temperature and set to "Auto". The automatic temperature control should now engage the compressor clutch and provide cool air within a minute, if the system is properly filled and the compressor in proper condition. Go back to normal temperature (70°F or 21°C). The clutch should start working (on/off) and engage/disengage the compressor clutch after a while.

Note: The automatic temperature control may still provide error codes 10 and 11 after this fix is applied and the control unit working. I suspect, this is caused by the fact, that the original transistor design used in the blower speed control is driven by current, while the new power MOSFET is driven by voltage (very low current signal). The resistor in the signal line will ensure to protect the control unit in case of failure. Not sure, how the temperature control really is designed internally. Didn't have a look inside.

Please correct me, if I'm wrong with my assumptions. This fix works at least for me, is based on reengineering the original shop manual and voltages found in my car.

I have started a test phase for my fix and will provide results soon.

Hope, you enjoy my modernization of our cars.

Best whishes!

mkvii
Last edited by MKVII on Wed Jul 08, 2015 1:55 pm, edited 7 times in total.
My other car is a Lincoln.
Lincoln Mark VII Continental 1984, Corvette L-82 1979, Pontiac Firebird 1994

ImageImage
User avatar
MKVII
CLUB MEMBER
 
Posts: 96
Joined: Wed Apr 30, 2014 2:36 pm

Re: How to: Fix broken blower speed control / compressor clu

Postby CDW6212R » Tue Jul 07, 2015 6:22 pm

Interesting, and I've bookmarked this page. Thanks for the time you spent working on that.

I need to make the time to research how the system works, and how close the EATC from the 97-01 Explorer may be. I want to attempt to upgrade to that EATC, 98+ has a PWM controller, and the buttons are much bigger, all illuminated etc. Regards,
Don
1991 Red Special Edition, my 2nd SE, dead paint, DWS 255/45/17's on 95 Cobra wheels, and soon; DVD/Navi/backup camera, OBDII and the 347, before custom paint.
98 Mountaineer with Continental DWS 255/55/18's, big sway bars, custom brakes. Soon to be A4WD with XP8 bumpers and wing.

ImageImage
User avatar
CDW6212R
CLUB MEMBER
 
Posts: 5536
Joined: Wed Feb 09, 2011 11:57 pm
Location: Near Dollywood in TN

Re: How to: Fix broken blower speed control / compressor clu

Postby Falkon » Tue Jul 07, 2015 11:29 pm

OR, run a 12 volt ignition source from your fuse box to a simple toggle switch under the dash. The other end to the green wire feeding power to the pressure switch under the hood. I turn it on to get the compressor working. It cycles OK. If you forget to turn it off, it's w/ the ignition. Not as perfect, but 10 minutes work.
User avatar
Falkon
CLUB MEMBER
 
Posts: 266
Joined: Sun Dec 22, 2013 2:49 am
Location: Wisconsin

Re: How to: Fix broken blower speed control / compressor clu

Postby lpjbird » Fri Jul 22, 2016 4:01 pm

Falkon wrote:OR, run a 12 volt ignition source from your fuse box to a simple toggle switch under the dash. The other end to the green wire feeding power to the pressure switch under the hood. I turn it on to get the compressor working. It cycles OK. If you forget to turn it off, it's w/ the ignition. Not as perfect, but 10 minutes work.


Kind of an old post but I thought I'd give a big kudo's for this little piece of advice. I've been screwing around off & on for two years trying to track down my wiring problem causing the compressor clutch not to engage. I read this and had the air cooling my butt in about 30 minutes. sometimes we just need to take the easy road & it makes all the sense in the world. I had two repair shops tell me it was going to be a major ordeal to get the air working & cost at least $400.00. I did this for $4.00 for the switch which I didn't have and twenty minutes time. God Bless You Falkon! Now if I could the speedo, odometer & gas gauge to work again or light up I'd be one happy camper..
Image
JR Bondy; Is the proud owner of a 1985 Continental Base -w- 5.0
If I knew I was gonna live this long I would've taken better care of myself. (Bobby Lane)
User avatar
lpjbird
REGISTERED USER
 
Posts: 38
Joined: Sun May 05, 2013 10:37 am
Location: The Motor City/Metro Detroit

Re: How to: Fix broken blower speed control / compressor clu

Postby CDW6212R » Sat Jul 23, 2016 2:57 pm

lpjbird wrote:
Falkon wrote:OR, run a 12 volt ignition source from your fuse box to a simple toggle switch under the dash. The other end to the green wire feeding power to the pressure switch under the hood. I turn it on to get the compressor working. It cycles OK. If you forget to turn it off, it's w/ the ignition. Not as perfect, but 10 minutes work.


Kind of an old post but I thought I'd give a big kudo's for this little piece of advice. I've been screwing around off & on for two years trying to track down my wiring problem causing the compressor clutch not to engage. I read this and had the air cooling my butt in about 30 minutes. sometimes we just need to take the easy road & it makes all the sense in the world. I had two repair shops tell me it was going to be a major ordeal to get the air working & cost at least $400.00. I did this for $4.00 for the switch which I didn't have and twenty minutes time. God Bless You Falkon! Now if I could the speedo, odometer & gas gauge to work again or light up I'd be one happy camper..


I'd be careful about running the high AC clutch current through a switch on the dash. That might be a decent temporary solution, but high current over time kills electrical components, like all of the factory switches in the dash, and the EATC itself. That's why in the 90's most auto makers began reducing high currents that have to go through fragile switches etc. That's why newer cars have so many fuses now, and a lot more relays.

I had a similar current loss in my AC clutch circuit, and I didn't hunt it down once I knew it was a lack of current. I stopped the system from attempting to push high current through the EATC. I cut the wire from the AC clutch to the WOT relay(next to battery). I installed another relay next to the WOT relay, and powered it, to feed the AC clutch using the old feed end, from the WOT relay. It's one extra relay and short wiring, and now low current from my EATC triggers the AC clutch(by the new relay). That is the safe way to power the clutch, it will last that way indefinitely.

I only did it using a handy aftermarket relay for short term use, so it doesn't look pretty at the moment. I will be rewiring the whole car soon, so that extra relay will soon be inside the Power Distribution Box along with the other under hood relays and fuses. So a picture of mine is posted elsewhere on the forum, but it isn't elegant, I just laid the relay down next to the existing wiring and relays.
Don
1991 Red Special Edition, my 2nd SE, dead paint, DWS 255/45/17's on 95 Cobra wheels, and soon; DVD/Navi/backup camera, OBDII and the 347, before custom paint.
98 Mountaineer with Continental DWS 255/55/18's, big sway bars, custom brakes. Soon to be A4WD with XP8 bumpers and wing.

ImageImage
User avatar
CDW6212R
CLUB MEMBER
 
Posts: 5536
Joined: Wed Feb 09, 2011 11:57 pm
Location: Near Dollywood in TN

Re: How to: Fix broken blower speed control / compressor clu

Postby lpjbird » Sat Jul 23, 2016 3:49 pm

Thanks for the warning. I'm not sure what your saying about having an effect on a switch or any of the other switches. I'm not a electrical guy by any means but have some experience. What I did was tap power from the cigar lighters circuit run it through another 20amp fuse I added to a 30 amp Rated switch I mounted next to the climate control run the power feed to the existing connection at the clutch, cut the existing power & ground connection and spliced it to my new power feed wiring, along with the ground & that's it. I don't see how anything else would be effected. Does that sound right or am I missing something? It appears to work as it did before except now I have a switch to engage or disengage the clutch. My concern is, does a clutch run continuously or does it switch on & off throughout the time the Air is on? I assume it's engaged the whole time your running the air conditioning, right? Thanks
Image
JR Bondy; Is the proud owner of a 1985 Continental Base -w- 5.0
If I knew I was gonna live this long I would've taken better care of myself. (Bobby Lane)
User avatar
lpjbird
REGISTERED USER
 
Posts: 38
Joined: Sun May 05, 2013 10:37 am
Location: The Motor City/Metro Detroit

Re: How to: Fix broken blower speed control / compressor clu

Postby CDW6212R » Sat Jul 23, 2016 7:12 pm

The AC clutch requires a good bit of current to run it. That high and not low current is hard on wiring and switches etc, and long term it can make things brittle or fail. Check out an old car's wiring, the electrical components in a dash. They will all be discolored, the wiring will be brittle, and that's the thing that makes switches etc, die.

I don't know what power source you have feeding the clutch, other than it sounds like constant ignition power. That is saving the EATC and the dash wiring that were handling that current before. But the power is still hard on the wiring you have it going through, the pressure sensors, and the switch too. That should be fine for months or years with no trouble. But I wouldn't have gone that route if I knew of something else to do. What I did is automatic because the EATC is still controlling when the clutch runs.

I just used a new relay for its best use, to reduce current from having to run through long wires, the dash, the fragile EATC controller, and the pressure sensors. I don't know what had reduced the current through my clutch circuit to keep it from being able to run the clutch. But I bet the cause was the high current that's been going through those many parts for 22 years. If I owned any other cars that have the full clutch current running through the dash and controller, I'd install a relay ASAP to lengthen the lifespan of the old wiring etc.

I should create a How To thread for this, I'll try to someday, or maybe a member here will take it on and make it. I didn't do it to look pretty or OEM because I knew I'd be changing it soon. But it would not be hard to alter the relays a little there next to the starter solenoid, on the fender.

Here's an old picture of it, years back before I discovered my fabricated battery cable corroded and replaced it with an OEM better part.
Image
Don
1991 Red Special Edition, my 2nd SE, dead paint, DWS 255/45/17's on 95 Cobra wheels, and soon; DVD/Navi/backup camera, OBDII and the 347, before custom paint.
98 Mountaineer with Continental DWS 255/55/18's, big sway bars, custom brakes. Soon to be A4WD with XP8 bumpers and wing.

ImageImage
User avatar
CDW6212R
CLUB MEMBER
 
Posts: 5536
Joined: Wed Feb 09, 2011 11:57 pm
Location: Near Dollywood in TN

Re: How to: Fix broken blower speed control / compressor clu

Postby oldschool1 » Sun Aug 07, 2016 8:24 pm

lpjbird,

I'm a little foggy on your clutch correction but here's how it sounds to me:
You took power from a cigarette lighter and ran it to a fuse,
then to a switch,
then to the A/C clutch.
Is that correct?
If so, yes, this will engage the clutch every time the switch is closed (turned on) by you.
Should it run at all times? No. An integral part of the system is the three way pressure switch atop the dryer that says the clutch can only be engaged when the system pressure is between two preset pressures. It prevents the clutch from operating if the pressure is too low or too high. Unless you're absolutely sure of the pressures at the three states (off , operating, and high pressures), then I would not operate the system in this manner.
User avatar
oldschool1
CLUB MEMBER
 
Posts: 8769
Joined: Fri Dec 26, 2008 10:01 pm
Location: Primos, Pennsylvania USA

Re: How to: Fix broken blower speed control / compressor clu

Postby cfcjr » Tue Aug 09, 2016 11:44 am

John
I have been operating with a switch under the dash for at least 4 or 5 years. (too old---Can't remember) I have not had any trouble. I didn't use cigarette lighter, as I wanted it to turn off if I forgot to switch it off.
Image
Charlie
2013 Lincoln MKS 3200 Miles
2007 Grand Marquis LS 50,000 miles
2005 Ford Five Hundred Limited 145,000 miles
1989 Lincoln Mark VII LSC 90,000 miles
1968 Cougar "XR7"
User avatar
cfcjr
CLUB MEMBER
 
Posts: 290
Joined: Sat Dec 27, 2008 10:41 am
Location: Dartmouth, Mass.

Re: How to: Fix broken blower speed control / compressor clu

Postby lpjbird » Tue Aug 09, 2016 12:51 pm

Thanks, I was getting worried about it although I can't understand how it would cause a problem. I used the cigar lighter circuit because it was easy & im lazy or just wearing down on working on this car. I can spend hours trying to get certain things to function with ZERO results! Nothing worse than coming up empty after 8 - 10 hours. This car seems to fight me every step of the way, the air dryer for the suspension has me fit to be tied. I've replaced O rings, grommets, washers, even put a new one on, or tried to and it still leaks air at the 4 air outlets. I'm ready to sell but would like to get things right before I do instead of trying to explain why the car doesn't stay up. And the instrument cluster, i.e. Speedo, fuel, odometer don't light after dozens of attempts looking for reason, I'm half nuts! Oh gee sorry for the rant, at least I'm cool now eh... Thanks again for the reassuring words.
Image
JR Bondy; Is the proud owner of a 1985 Continental Base -w- 5.0
If I knew I was gonna live this long I would've taken better care of myself. (Bobby Lane)
User avatar
lpjbird
REGISTERED USER
 
Posts: 38
Joined: Sun May 05, 2013 10:37 am
Location: The Motor City/Metro Detroit


Return to Electronic

Who is online

Users browsing this forum: No registered users and 1 guest

cron