Carrera A/C fan speed -- an idea
 

The A/C fan control on the Carrera cars has three operating speeds: I -- too slow, totally useless; II -- Not bad but sometimes too slow; III -- High but too high most of the time.

I have been thinking one of those variable speed controls would be nice to have a speed between II and III, but they're expensive.

It occurred to me that the speed control operates through resistance to control the the fan speed. Why not just reconfigure the resistance levels so speed setting I operates like current speed setting II, speed setting II is that perfect "most of the time" speed between the current speed settings II and III, and speed setting III remains unchanged.

I'm no electronics expert but it would seem to be an easy fix once the appropriate resistors are selected.

Can any of the electronics gurus on the board comment on this? Can these parts in the speed controller be simply replaced with electronic parts to achieve different fan speeds for the three settings (pic below from another Pelican thread)?

http://forums.pelicanparts.com/uploa...1150714456.jpg

Thanks!

Looks nice...but at $300.

John, I went thru this with the footwell blowers and posted a schematic of the modified circuit awhile back. I wound up using some very beefy 100watt resistors to give me the speeds and the safety margin that I thought where right.
The A/C resistors could be changed to different values but if you wanted them in the same location then you would have to buy some resistance wire and roll your own.

I was also looking at the Griffiths fan controller yesterday but was wondering about the overall air moving efficiency of the AC fan itself. Is it possible to replace the stock fan with an upgraded model that moves more air at each fan control setting? Could an upgraded fan also move the same level of air as the stock fan with a lower noise level (the current high setting seems to be too loud relative to the amount of air actually being moved through the vents).

I know the variable speed unit is available. I'd like to have it but it is expensive. Perhaps just changing some resistance could accomplish a satisfactory result (with three reasonable fan speeds) with little expense.

Not as good as completely variable but what if it could be done for $30 or less instead of $300?

If you just mess with the resistance, you will get lots of heat from the resistors and a varying fan speed.
The best way is to limit the voltage and/or current flow through the fan.
A simple variable voltage regulator would be inexpensive and work well.
If you go this route, look for the correct reg that will supply the correct current without blowing up the regulator.
Place a current (ampmeter) inline with the fan on high speed to determine the necessary flow.
Then multiply by 2 to get the correct regulator (so you never have to replace it because it blew up)!!
Then put a pot (variable resistor) to control the output of the regulator and you are there!
Infinite control, the easy way.
Have fun
Bob

John,

Can you measure the value of those two resistors?

A large rheostat in the 50 Watt - 150 Watt range would probably be able to do just what you want!

Here are a few examples on eBay:

http://cgi.ebay.com/Miller-Rheostat-P-N-603942-5ohms-5-48Amps-150W-NewNR_W0QQitemZ150013090270QQihZ005QQcategoryZ5816 4QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/New-Ohmite-Rheostat-w-Power-Switch-30-Ohms-50-Watt_W0QQitemZ260012280943QQihZ016QQcategoryZ58164 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/CLAROSTAT-25-OHM-RHEOSTAT-UNUSED_W0QQitemZ250010262301QQihZ015QQcategoryZ466 4QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

http://cgi.ebay.com/CERAMIC-RHEOSTAT-OHMITE-6-9-OHM-500-WATT-RESISTOR_W0QQitemZ170009829880QQihZ007QQcategoryZ4 664QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Check http://www.mrjaguar.com/porscheac/porsche930turboairconditioning.html. They have both the variable speed fan controller $259 or an improved motor assemby for $159.

Bad link, check here
http://www.mrjaguar.com/porscheac/ check 930turbo upgrades

Interesting idea Warren. Thanks, DonMo. I actually got my entire AC upgrade kit from Mr. Jaguar AKA Retroair. They are just a few miles from where I live. My AC works great. In Dallas 105 degree temps this weekend, I got 35 degrees on medium fan speed and 40 degrees at high out the center vent.

Yes, they're working on a variable speed controller, but with this thread I was hoping to do something simpler and cheaper but almost as effective. To me the challenge is just getting a fan speed that falls between II (too slow) and III (too high). Since the existing control seems to operate off resistance (I assume those spring looking wires are used for that) I hoped replacing them with selected resistors would let me change the three speeds to those of my choosing.

How about a DIY electronic kit for a PWM controller for 12v dc motors? Wire up this kit, remote-mount the potentiometer (in place of the off-1-2-3 speed switch in the console) and place this controller near the evaporator.

http://www.electronickits.com/kit/complete/motor/ck1400.htm

Brian,

Very good idea, and a concept I briefly considered preferable to the 'brute force' rheostat ... but, not being aware of that particular kit with such a high rating [circuit board traces should probably have some 14 ga runners added as a precaution] ... figured it would be 'beyond the scope' of most board members!

Nice find, Brian. Good, inexpensive concept. I just checked the fuse box on my '89 and, unfortunately, my AC fan fuse is 25A a little too big for this kit to handle. Rats.

<that particular kit with such a high rating [circuit board traces should probably have some 14 ga runners added as a precaution]>

Warren: I am looking forward to installing this kit this winter. The documents claim 100v 7 amps -- and I assume that the 7 amp rating applies at 12v also. I assume that the "runners" are installed in parallel to traces on the PCB. The question is: which traces need the supporting runners?

Jastx,

I'm away from home for a couple of weeks without access to my manuals, but does the 25A fuse handle the evaporator fan, the condenser fan, and the compressor coil?

Brian

John,

Fuses are typically rated for a 125% overload, so that kit with stated 16 Amp capacity for the MOSFET will carry the motor load safely ... you would need to beef-up the circuit board trace by soldering a hand-formed piece of 14 ga or 12 ga wire to the board from the Source and Drain leads of the IRF530 device to the load terminals.

Warren,

So, correct me if I'm wrong. There would actually be 4 individual runners installed from the IRF530:

Source (S) to ground at #5 or #6 on X1
Drain (D) to D1
D1 to C7
C7 to #4 on X1

Right?

Guys, I've been doing some searching on this too for some time. I'm amazed at the cost of most of the commercially made units. I'm not surprised now at the cost of the Griffith's unit. Brian's find is certainly the best by far, but I'm wondering how much speed control really is needed? The electronic route would certainly be a fun exercise, but as mentioned earlier on, wouldn't it just be simpler to make setting II, the first speed, and make a speed in between the current II and III. Wrap some wire and your done. Just have to find the right kind of wire.

Brian,

As I see it, you would want to use strictly the external power supply option, so jumper LK1 would be left open. E+ and V+ would be jumpered externally from X1 terminals #2 to #3 with a 12 ga or 14 ga wire.

The heavy, add-on jumpers would essentially be straight from the MOSFET Drain to motor lead M- [X1 - #4] and MOSFET Source to ground terminals E- and V- [X1 - #5 & #6].

Here is a closeup of the assembled board:

http://www.kitsrus.com/jpg/k67_2.jpg

Actually, at this time of year in Florida, the speeds are I. Is this thing on? II. Okay on a cool night and III. Barely adequate when the sun is out as long as you have one of those windshield thingies to use when you park outside.:D

Warren,

Got it! Thanks for the instruction and clarification. I'll put this together this winter.

<E+ and V+ would be jumpered externally from X1 terminals #2 to #3>

In this statement, I suspect that "E+ and V+" should be "E+ and M+", which are the #2 and #3 terminals shown connected by a PCB trace.

Brian

Guys, I ordered one of these kits and took some time to check it out today while procrastinating on a transfer case reseal project.

The kit as delivered indeed is limited to about 16 amp with the included IRF530 Mosfet if you beef-up the traces. Interestingly, the directions and component list shows that the kit was originally designed with a IRFZ44N Mosfet which has an amp rating of 49a at 30C. I'm guessing that they are substituting the IRF530 due to the trace limitations and cooling limitations of the kits sealed case and of course, cost. In our situation I'm thinking that the board would be installed similar to the griffith's unit/stock resistor pack, so that the heatsink would be cooled by the inlet air to the evap. Now I just need to figure out how to solder this thing together:)

Anxiously awaiting outcome......

If you do that, won't your speed controller, the pot, be mounted under the passenger seat floor board?

Regards,

Jerry Kroeger

This thread is getting interesting.

SC-targa -- regarding the speed controller on the board, you could mount the pot remotely, I'm sure, but...

turbocabmike restated the premise of my original post: "wouldn't it just be simpler to make setting II, the first speed, and make a speed in between the current II and III? " Just modify the existing controller a little?

Keep the ideas coming!

SC-targa, yes as the kit is configured, but my plan is to mount the pot in place of the standard fan speed control and run a 3 wire harness to the electronic speed control mounted where the stock resistor pack is now under the floor board. I'm currently waiting for the higher rated mosfets to arrive. They only cost about $1.50 each, but in typical fashion, the cheapest shipping I could find was $9.00, so I ordered 10! That means that the first 9 who want to do this conversion can contact me for an upgraded mosfet for cost plus a stamp:)

I researched just fabricating a new resistor coil, but this type of electronics isn't my thing, I couldn't figure out what was the proper wire and this kit is pretty darn cheap weekend fun building it with my kids, soldering and discussing electronics. I'll keep you posted.

89turbocabmike,

Put me inline for the upgraded mosfet.

THANKS!

I had looked at the Griffiths fan controler but the price was not justifiable. Is this something that can be upgraded by the electrically challenged? If so, put me down for one.

89turboCabMike

Sent you an email regarding one of the MOSFETs you have.

Brian

Re: Carrera A/C fan speed -- an idea
 

Jastx,
Yes. You can simply replace the current resistance values with your own personal choice.

Before we designed the <b>Kuehl Variable Fan Speed Controller </b> we experimented with various values of resistance to raise the original fan speed "1" to that of "2", made original "2" something between original "2" and "3".

However, in the end, we found some clients wanted one set of values and others wanted something else; and you have different air distribution requirements between the pre 86 model and the 86 post model dashes; and then we had clients with vent air noise issues.

Next we considered a "rheostat" perse, since the resistance value could be changed at the fan speed switch location. But, when you investigate further you will find you need a rather large variable pot that typically gets very very warm and location became an issue.

So the <b>Kuehl Variable Fan Speed Controller </b> became the ticket to satisfy a wider array of client needs; with any speed they wanted.

Getting back to your approach of three fixed speeds:
You'll need a resistor(s) that can handle the wattage. If you look at the OE resistor pack design you'll see the wound resistor wire size used and you'll note the thermal shutoff point set they incorporated as well; so remember that heat and safety is an issue. Your evaporator motor current requirements x voltage are your guide to wattage ratings. Don't forget to consider your evaporator motor's present "condition" before you start experimenting with resistance values.

The OE resistor pack has the resistance values stamped on the resistor supports, so you can take it from there in figuring out where you want to go. A fairly well known resistor firm is Ohmite, http://www.ohmite.com/cgi-bin/products.cgi
look at their WLRH Series or the Aluminum Housed axials,
and there are other options.

89turbocabmike,

If still available, put me inline for the upgraded mosfet. Thanks. Paul.

Well, board is soldered except for the pot. I need to source some 3 conductor wire to remotely mount the pot in the stock location. Went together very easily in about 20 minutes, this being my first circuit board kit. I've got alot of general automotive soldering experience, but this takes a bit more attention to prevent overheating the components. I used some of the larger gauge solid wire trimmed from the components for jumpers. I'll try to get it all together and hooked up for a test tomorrow nite as I have my Evaporator motor out for lubing.

I've also got Rennaire's Desert-Duty front serpentine condensor and Evaporator as well as a Parallel flow condensor to replace the stock turbo tail condensor. Hope to have everything installed in the next couple weeks.

I've still got a 5 upgraded mosfets for those that need them.

http://forums.pelicanparts.com/uploa...1154929271.jpg http://forums.pelicanparts.com/uploa...1154929290.jpg

89turbocabmike,

I suggest plenum-rated Cat5E or Cat6 comm cable from a superstore ... more conductors that you need, but better & tougher cable sheath, too!

Thanks Warren, that's a big help!

Late night update. I found a 4ft length of cat5 in my misc. wire stash and hooked up the potentiometer. Here are my preliminary findings hooked up to a new fully charged optima and my evaporator fan. With the fan running the input voltage is reading 11.9v and the speed control varies the output voltage from 7.4v to 10.6v. Adjusting the trim pot has little discernable difference on fan speed and with my multimeter I only saw a very small variation of about .04 volts while playing around with the trim pot. I'm disappointed not to get a higher voltage output to the motor. With the fan connected directly to the battery there is a big jump in speed with the extra 1v. Of course things will change once installed as operating voltage with the car running is quite a bit higher. I'm not sure what I should have expected though.

89TurboCabMike:

I meant to answer this back in August, and got sidetracked. You mentioned less-than-12v input to the motor. If you were using a regular voltmeter, it makes sense that you saw a range of voltage, all below 12v. The unit puts out a Pulse Width Modulation signal, which means it puts out 12v for a very short period, then shuts off for a short period, then 12 v for a short period, ....... etc. The width of the pulses (usually measured in milliseconds of ON time) determines the speed of the motor. Your voltmeter reads it as an average voltage, so add up the pulse widths in a second and divide by 1000. 500 ms of 12v and 500 ms of 0 v would reflect 6v on your meter. The motor sees it as 12v, then 0v, then 12v ....

Brian

89turbocabmike:

I finally got my system assembled and working. I noted the same enexpectedly low speed on the motor that you did. In reading the instructions for the PWM unit, I noted that you could short across R1 to raise the speed. When I did that, the fan runs just a little slower that it previously did thru the stock wiring. The instructions mention experimenting with different values of R1, but it runs fine now, so why experiment? I do not know if you can run indefinitely with a short across R1 -- maybe Warren will chime in here.

This installation -- after a year -- was precipitated by a second occurence of a failed fan speed switch. The switch overheated and fell apart, offering a really good opportunity to finally install the variable speed switch.

Brian

So, is this kit the answer for an upgraded fan switch?

89turbocabmike, do you have any more of the upgraded mosfets left?

Thanks,