Blower motor circuit inadequate

Jack Houpe

GT40s Supporter
I made a comment of the wiring of SPF cars. One of the issues that I found inadequate was the circuit for the blower motors. If you look at the wiring diagram and follow it out it uses no relays to control blower motor current. It all goes through the ignition switch which then feeds the blower motor switch which uses a combination of resistors to change the speed of the blower, this is ok BUT the wire size is undersized for amount of current of the total circuit and the switches are undersized. Example I noticed that when the blower motors (2 of them) were on high and came to a idle with my car the blower speed decrease considerable. After pulling my switch panel off I noticed the main power feed to the rotary switch (blower speed switch) and the wire going to the HIGH position to the blowers to be brown from excessive current draw. I replaced the terminals and did not pay any more attention to it. During my open road race I had the fan on high while driving the event with the AC off to keep cool in SW Texas. After the event I went to turn my key switch off and it was hot to the touch. This concerned me so after returning home I looked at the circuit overall and found that the wires going to the blower motors are much smaller than the wires from the motors to the plugs on the harness. The motors draw 8 amps each or 16 amps total on high, the keyed switch is rated at 15 amps max, I am sure the switch on the dash is rated for even less. Overall the wire size and switch size become resistive under high current draws. The correct fix would to be replace the wires going to the blower motors with a larger size and to use a relay to feed that circuit and not have all the current go through the keyed switch. I elected to use a PWM (pulse width modulator) to control the speed of the motors doing away with the rotary switch and replacing with a rheostat and running new wires to the high (orange wire on the blowers) side of the motors. I also used a relay off the keyed switch to control the current of the motors and a auto reset breaker for protection. This system works very well and there is a noticeable increase of CFM at idle and under way. The PWM are less than $30 on ebay but all this will require some soldering skills and wiring of the correct size. Mike Trusty and Kirby Schrader have also done the same with there cars with the same success. The diagram attached is for the circuit which I have described. The relays in the circuit are NOT for the blower but for the small servo motor that reverses for the recirculate servo motor.
 

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Jack Houpe

GT40s Supporter
Mike, here is the ebay item which will work, they are using these PWM to make hydrogen gas from water. The Pulse Width Modulator works like someone turning a switch to the blowers on and off very very fast. So the motors do not see a drop in voltage thus reducing speed but rather a series of pulse's that make it operate at a slower speed. This unit will operate the motors but you might want to spend the extra few dollars for a 30 amp unit to be extra safe.

12-40V 17A 200W DC Motor Speed Control PWM Controller - eBay (item 160348230932 end time Aug-11-09 06:05:35 PDT)

The fix will require to you unplug both blowers from the factory car harness run a #14 wire to the orange (orange is high speed NOT red) wire on the blower motor using a female spade terminal and also a #14 wire to the black wire going to the blower using the same. You must do this on BOTH motors. The first motor and easiest one to get to is under the fake oil tank in the front of the car. The second which is a little harder to get to is under the panel just under the window which is opposite the brake and clutch reservoirs.

Remove the old blower switch, replace with rheostat (I used the old knob to on the rheostat for looks) You may have to lengthen the wires dependent where you put the module. Kirby, Mike and I had to unsolder the rheostat and add wires but this unit looks to have it remote already. One important piece of information is that the GROUND or the -negative black wire is the wire that is pulsed. Do not try to cheat and just ground the black wire to the car it will fry the PWM. You must run two wires to each blower motor. They connect together at the modulator. For power I came off the amp-meter circuit (HOT ALL THE TIME) and went to a standard 20 amp auto reset breaker and from there to a standard 30 amp relay which is turn on by any switched 12V. This way you isolate the blowers from all the other circuits to a circuit that is protected and healthy enough to push the motors. All the parts you can buy at any auto parts store except the PWM. Hope this helps. Kirby, Mike and myself all notice the difference and it is safe.
 

Jack Houpe

GT40s Supporter
Guys, Lynn has posted a SPF fix for this problem. I knew nothing about it, just that the system was inadequate. Guess others have had problems also. I will mention that the wires that feed the blowers are still to small in my opinion. Lynn has asked me to take pictures of the system I built for my car and post in the HOW TO section. I will do so soon as I get the front bonnet off the car.
 

Steve C

Steve
GT40s Supporter
Jack,

Great fix but, I believe the SPF relay pack fix is adequate.

I have the SPF relay fix and believe it's OK based on wire size and wire address as used (feed isn't through the key switch, loads shared, switch to relay coils ect)

I've been running it now for >3,000 miles usually with the blower fans on high for A/C or just ventilation and have not noticed wiring to the blowers getting warm.

If you haven't take a look at the SPF fix and let us know if you agree and if not why.

Tx, Steve P2125
 

Jack Houpe

GT40s Supporter
Steve, I agree with the fix, I just didn't know about it before today. I am concerned about the amount of current going through those wires but if they haven't melted by know then your fine. I will tell you that taking the relay fuse panel out is much harder than my solution. Its a bear to get out, have plenty of bandaids if done by the owner. :)
 
Jack

I may have misunderstood your comment but there is no need to remove the relay pack to do the fuses 12 Fix. It's an install that takes about 20 minutes to perform. check out the "How To" I posted this AM.
 
I elected to use a PWM (pulse width modulator) to control the speed of the motors

...taking your cue from Marvin the Martian I suppose:

Marvin-marvin-the-martian-740116_538_350.jpg


and his Illudium PU-36 Explosive Space Modulator.

"Where's the Kaboom? There's supposed to be an earth-shattering Kaboom!" :laugh:
 

Jack Houpe

GT40s Supporter
Jack

I may have misunderstood your comment but there is no need to remove the relay pack to do the fuses 12 Fix. It's an install that takes about 20 minutes to perform. check out the "How To" I posted this AM.

Sorry Lynn I misunderstood the first time I read it. After looking at the fuse and relay I see they are not from the car. You are correct.

If SPF provides this kit it would be the way to go. If not then my ebay fix would work too.
Jack
 
Sorry Lynn I misunderstood the first time I read it. After looking at the fuse and relay I see they are not from the car. You are correct.

If SPF provides this kit it would be the way to go. If not then my ebay fix would work too.
Jack

Jack, I'm not sure what the status of SPF supplying these repair kits is. Very few dealers are even aware of the problem and hence few owners are either (until it rears its head). I got the first kit because I was in on the "fix". I contacted all the owners I knew at the time and informed them myself. Some had a tough time getting their dealers to respond others didn't respond at all. I believe Rich Woerz got his kit directly from SPF (not sure). Anyone feeling the need for this should contact there dealer or SPF to get the parts. I like your fix also. I'll post a "How To" when you get your pictures in order.
 
After talking to Lynn many monthes ago, I got my repair kit from Dennis Olthoff. Didn't seem to be a big deal to get one.

Lynn, thanks again for all your help. We need to get in touch again, its been tooooo long.

John
 
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