Carrera A/C fan speed -- an idea

[Jastx]

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)?



Thanks!

[Mysterytrain]

http://www.griffiths.com/porsche/ac/911ac/index.html#Controls

[RickM]

Originally posted by Mysterytrain
http://www.griffiths.com/porsche/ac/911ac/index.html#Controls

Looks nice...but at $300.

[Mysterytrain]

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.

[dmwallace]

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).

[Jastx]

Originally posted by Mysterytrain
http://www.griffiths.com/porsche/ac/911ac/index.html#Controls

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?

[HawgRyder]

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

[Early_S_Man]

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

[DonMo]

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

[DonMo]

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

[Jastx]

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.

[cmonref]

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

[Early_S_Man]

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!

[Jastx]

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.

[cmonref]

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?

[cmonref]

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

[Early_S_Man]

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.

[cmonref]

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?

[89turbocabmike]

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.

[Early_S_Man]

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: