355 Need info on HVAC dash vent actuator

I'm trying to find a cheap substitute for the dash HVAC vent actuator motor. They are a dime a dozed and it should be easy to adapt one to the 355 for the NLA and over priced Ferrari unit. If you have an old one around perhaps you can give me the info I need. You will need an ohm meter. The plug on the actuator has 5 connections as shown below. I need to know the resistance between yellow and green pins.

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2,275 ohms or thereabouts.

3.8 ohms between purple and green

2278 between purple and yellow.

I can't figure out why the purple & yellow is bigger than the yellow and green. The values change as you would expect when the drive rotates.

This was with the drive fully anticlockwise (as seen from the side opposite the shaft).

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The small notch in the drive was pointing down (due south on the compass).

45 ohms on the motor wire

 

Internal circuit here:

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Yellow to Green - 2275 doesn't make sense (to me).

Yellow to green must = (purple to green) + (Purple to yellow) = about 6k.

(assuming unplugged from harness)

 

New (unused) actuator unplugged. Sitting on desk

It's (approx) a 2.28 K potentiometer.

3.8 ohms plus 2278 ohms = 2281 ohms.

This is the measured position...

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As I said, the values change normally on the correct wires.The green to yellow value doesn't change. The other values do. I've checked and rechecked today and previously. It's weird, but I don't think there are any additional electronics inside. Perhaps just a wide contact point on the slider with surface irregularities.

 

Ok, I was reading 3.8 as 3.8k.

2.28k makes it tough. All the ones I have tested are 10k.

 

At the half way point (90 degrees of rotation), purple to green 891, purple to yellow 1458. Total 2347. I reversed the leads to see if there were any diodes in the circuit, but the values were the same.

(EDIT) Ok, only 72 ohms out on a 2.28K pot... and the sum is greater than the potentiometer (2.28k), but that is to be expected.

 

It's just a pot. I'm asking about this because I can't find my old one. May not be linear taper. But as you say, may just be due to the size of the contact point.

 

You need a linear pot and, if half-rotation is 90 deg. as Ian informed, then the pot should be a bit more than 180 deg. Without checking the total rotation (do not have a spare actuator), I bought, a couple of years ago, the three pots shown on the attached table ("easywayelc" was the Ebay seller). Now I see that the 188 Deg. one should be just right. It is 5K as I could not find anything smaller but it should work fine as the signal being sent to the AC ECU is the voltage from the wiper (the middle pin) representing position of the flap. There is probably 5V supplied by the AC ECU to the end pins of the pot so the voltage on the wiper, when in mid position, will be 2.5 volt irrespective of whether the pot is 2.3 K or 5 K or whatever.

I bought these pots to keep them as spare in case I need to, one day, repair my actuator but I do not know if one would fit inside.
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The pot is build into the actuator. I'm not looking for an external pot. I'm looking for an actuator that has the correct resistance pot built in. They are a dime a dozen. Just a matter of finding one with the right resistance. Though I had one that would work but it has a 10k pot.

For the re circulation flap it's pretty much a no brainier as the ECU doesn't track position.

There are also several gear replacement kits for these actuators. Might be able to find one the fits as well.

 

Are you referring to the gear on this actuator that gets stripped? If you do find a kit that matches, please let us know, I'm sure a bunch of us would like to purchase one. Thanks

 

That's exactly why I'm doing this. These actuators complete go for between $15 and $30 if I can find one that can be adapted. Gear kits are $5 to $10. I'd like to find a complete actuator because the original actuators come with different internals.

 

Has anyone tried to source these gears from a company called Rushgears.com? They claim that you can send them your gear and they can duplicate it. I am currently holding out to see if Takeya can help me get a new gear. Also, does anyone know if this particular actuator fit any other vehicle, or is it specific to Ferrari?

 

There is one for purchase, but not everyone is happy with the cost Contact Takeya in PM if you need one.

https://www.ferrarichat.com/forum/posts/147607798/

 

As I mentioned in my earlier post, the resistance of the pot should not matter, up to some reasonable value above the 2.3 K (meaning not hundreds of Kohm or Mohms). In monitoring the flap (pot) position, the AC ECU is not looking at the resistances of the pot but at the voltage on the wiper pin. When a fixed voltage is applied to the pot's end pins (5V, I believe, from the AC ECU in this case), the voltage on the wiper pin will depend only on the wiper position in relation to the end pins and not on the pot's resistance, thus, for a given pot (flap) position, a 10K pot will produce the same feedback voltage to the AC ECU as the original 2.3 K pot. The only difference, if a 10 K pot is used, will be that the max. Milliamps of the feedback signal that it can supply to the ECU will be lower than what a 2.3 K pot can supply. However, I don't think this is important as, I believe, the ECU is only "looking at" (sensing) the volts coming from the pot's wiper and not really drawing any current from it (possibly some Microamps). One of the ECU's chips (an Op-Amp Voltage Comparator) simply compares the voltage set by the flap position selector with the voltage coming from the actuator pot. If the pot voltage is higher or lower, the ECU will rotate the actuator motor (in the required direction) and stop the motor when the two voltages are equal.

It should not be difficult to wire temporarily a 10 K pot actuator (without connecting it to the flap) and then watch its movements/responses to the various selected positions on the AC control panel. Of course, the motor resistance of the actuator to be tested should not be lower than what the original motor has in order not to overload whatever ECU components that are running the motor and switching to cw and ccw. I also "investigated" which flap actuators, from other cars, may shape-wise be suitable for adaptation for 348/355. These are a few that I saved (I do not know their pot resistances):
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Yes, you are probably correct. It's just a simple voltage divider. Sometimes the old mind focuses on something and lock on. Anyway, this using I have should work fine in that case. $15. Just file/grind down the shaft to square with a beven on one corner.


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Yes, I have been in contact with him and hopefully he can get one out to me sometime in April. I would be surprised if the 348/355 are the only cars to have this particular actuator in it (maybe there is another European car that shares this part) ??

 

Do you need a bevel? The air distribution ones don't have bevels.

For info, the shaft is 6mm square.

 

Don;t know about the bevel. I was just looking at the recirc actuator (trunk) and it has a bevel so I figured the HVAC vent would also. But if it doesn't then none required.

And wouldn't you know it. I can remember where I put the $15 unit I bought. Turned 74yrs old yesterday. Must have left my mine at 73.

The unit has 6 pins. 2 for the motor, 3 for the pot, and one not used. Just need to make an adapter. The plug off the old actuator could be used as the male ened to the Ferrari harness and then splice it into a 6 pin connector for the new actuator. Then adapt the mount. The only issue now would be the angle of rotation from min to max.

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Anyway, this is the actuator I was looking at.

https://www.amazon.com/gp/product/B07XXKQZVN?pf_rd_r=XE7QZCFDDZZV2D9CAN8G&pf_rd_p=5ae2c7f8-e0c6-4f35-9071-dc3240e894a8&pd_rd_r=1c38c559-590d-4067-ab9b-196c8428fb76&pd_rd_w=ahQv3&pd_rd_wg=Pk5HI&ref_=pd_gw_unk

 

this is getting good........don't stop now.....certain there are a number of folks loving this one. Thanks

 

I would open it up (looks easy to do, held together by some plastic clips) and see what its total angle of rotation is. It is possible, instead of opening it, to just run its motor until it stalls at each end of travel and mark the positions to establish the angle but there is a risk of the stalls damaging something inside and your $15 is gone. In operation, these actuators never go to their mechanically extreme points but are stopped by the ECU somewhere earlier based on the pot readings. If the pot runs at 5V, the ECU will probably stop the motor at approx. o.5 and 4.5 volts at the respective sides of the rotational travel. In other words, the air direction flap does not need the full mechanical rotational span of the actuator or the pot but a shorter range within the full span of the potentiometer.

The mounting of the new actuator will include some careful aligning, probably using an adapter plate with slot holes. The alignment would have to be done by first bringing the actuator (prior to its connection to the flap) by selecting the "middle" position on the AC control panel, then positioning (and temporarily "jamming") the flap to exactly where it should physically be when in "middle" and finally plugging the actuator in and marking where to drill mounting holes on the (previously attached to the air box) adapter plate for it. Then, if after subsequent "live" actuator tests it becomes necessary to fine-tune the flap position, it can be done by rotating slightly the adapter plate (together with the actuator) as enabled by the slot holes in the plate at its mounting screws (that go into the original screw holes on the air box).

 

I already opened it up. The pot trace (black) runs 180*. I don't know what the 355 actuator pot runs (wish I could find my old one, I bet it's the same) but I know the vent can spin a full 360. So there would be no chance of jaming once installed. Just whether the positions would line up correctly. So this could be easily aligned by setting the vent to the "dash" position and the actuator at 90*. Then I think there would be 90* rotation in either direction and that should serve to move the vent from floor to defrost. I can't see mounting being a big deal. Sure beats $300 for a gear.

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Sorry, guys, this may throw a spanner in the works.

I just ran some more tests and found that the ohmmeter readings stop at 624 ohms at the fully clockwise position, as viewed from the non-drive side, with the lead pointing to the right,. i.e. with the notch up (due north)), not at 3.8 ohms. The half way readings must have been influenced by this.

So there must be drive limits not pot limits (at least at the clockwise position)

 

P.S. So the pot is fairly linear as Miro suggested.

2,275 ohms minus 624 ohms, divided by 2 to find the midpoint = 826 ohms. This is fairly close to the 890 ohms I measured at the approx. midpoint.