Door Opener on Reefer Container

Can you supply any more information?

You are not looking at the motor but rather a variable resistor that sends a feedback signal to the a controller telling what position the vent is in.

Is there something else on this shaft other then this variable resistor and the worm gear?


hi Mike!

It is indeed a motor as well. I took a video but not sure how to share via google docs. That said, you can see in the image the shaft of the spindle that drives the small cog that drives the worm gear.

The 3 wires go into a small inline device that reduces the cable to two wires. Perhaps this is some sort of shut off mechanism, and to drive it I simply need to reverse polarity - although not sure what sort of volts I should feed it to experiment.

That little diagram at the top of the black device in the photo looks like a potentiometer, and if I understood your comment about three wires going to two wires a pot can be wired as a rheostat (or vice versa) by connecting one two terminals together, and that can be used as a position indicator.

See the wording: RES 100K(ohm)? That means the device has a resistance of 100K ohms--which is how one would purchase a rheostat or potentiometer.

I'm with xtal_001--I think there is a motor driving the vent, and this shaft we see is driving the position sensor. It doesn't look like a motor, not from the drawing and indications on the outside. See Sh. 4 of this parts list:

Part number 10-00455 is described as a "Potentiometer lvps."

(I Bing'ed "CTD 10-00455". I also tried the 830- number at the bottom; didn't come up with anything.)

I suggest you go back to Clayton at EMR Christchurch and ask him nicely for a schematic for the reefer container you have (show him a photo of the nameplate). I think you'll find that the worm gear drives the "cog" which rotates the shaft of the pot/rheostat which sends a signal to some control system to indicate the position of the vent damper.

Hope this helps!!!
Thanks CSP,

Very helpful.

I had a closer look, and there is no other device that controls the very simple light closing door. So the device in question must integrate both a motor and the pot somehow. (If you look from the side, it is round and resembles a motor)

Thanks for your suggestions though, you have given me some good avenues to explore.


Many people have posted photos, docs, and videos on web hosting sites, such as They then post the URL to the file(s) in a response to (like you did with the link to the google docs photo). is free, but the files don't stay up for a long time--but long enough to let others view them to get you some comments and ideas.

If the round, motor-like device in the picture was a motor, it would either be a single-phase AC induction motor or a DC motor (and that would likely have brushes (which would wear out and result in replacing the device or the brushes). In either case, you said there were two wires coming from somewhere else in the electrical wiring bundle, and ended up at some intermediate termination with three wires coming out of the intermediate termination.

For an electric motor to change direction (to open and close the vent door/damper) either the single-phase AC being provided to the induction motor has to be switched to a different set of windings in the motor to reverse the direction, or the DC current/voltage being provided to the DC motor has to be reversed. Mostly, that would be done through some kind of switch or relay. And that switch or device would usually have to have at least one, maybe two, additional wires attached to it control the "direction" of the voltage/current being applied to the round, motor-like device to change the direction of rotation. Does the intermediate termination have more than five wires (two in and three out to the round, motor-like device)?

A potentiometer or rheostat which is used as a position sensor is often round, like a motor.

Lastly, I'm not clear on where the "cog" (gear) is mounted. In my experience, a rotating worm gear would drive a cog--so if the cog is mounted on the shaft of the round, motor-like device the worm gear would drive the shaft of the round, motor-like device; the cog mounted on the shaft of the round, motor-like device would not be turning the cog to make the worm gear turn. I have used my preferred World Wide Web search engine to look at images of worm gear mechanisms and it appears the worm gear turns to make the cog (gear) in contact with the worm gear to rotate--not the other way around.

I'm wondering if the air moved by the fan (I'm presuming there's a motor-driven fan somewhere) makes the damper move open (and gravity or a spring makes it move closed when the fan isn't running), and that makes the worm gear turn which makes the cog on the shaft of the round, motor-like device to turn, which changes the resistance of the pot/rheostat which is the indicator of the position of the damper.

I believe if the round, motor-like device were a combination motor and position sensor it would have to have more than three wires connected to it--but that's just a Scientific Wild-Arsed Guess (a SWAG). Again, to make a motor reverse rotation it would almost certainly have three wires connected to it--especially if it was an AC motor. A DC motor could have only two wires (which might be split into three at the motor terminals).

Seeing the video would probably be most helpful! It's just not clear to me where the worm gear is located and where the cog is located, and what does what to whom.

I was searching for a link to a worm gear picture, and I learned something: the thing I was calling a worm gear is actually a worm, and the round, multi-toothed thing I was calling a cog or gear is actually the worm gear. The assembly of the worm gear (sometimes called a worm wheel) and worm is called a worm mechanism. Something rotates the worm and that causes the worm gear to turn. Not the other way 'round; the worm gear can't rotate the worm, it can only shift it perpendicular to the axis of the worm gear.

In the video the worm is not visible--there's nothing in contact with the round worm gear.

What is the"stud" below the round worm gear and what is on the stud under the round worm gear?

Where is the worm?

Where is the movable door/damper?

If the worm is in contact with the worm gear at some point it would be parallel with the teeth of the worm gear (at a right angle to the shaft the worm gear is mounted on, and the cog can't make the worm gear turn. If the black, round, motor-like device on the shaft of the worm gear was a motor it could only shift the worm gear and the shaft it is mounted on "left" and "right"--like a rack and pinion mechanism. If the shaft the worm gear is mounted on rotated THAT would make the worm gear rotate clockwise or anticlockwise.

So, something would need to be rotating the shaft the worm is mounted on to cause the worm gear to rotate and turn the shaft of the black, round, motor-like device.

Look up worm gear or worm mechanism in Wikipedia, or with Google when the Search results page pops up you can click on 'Images' for a lot of pictures and drawings of worm mechanisms and/or worm gears.

I'm right now wondering if the thing on the shaft below the worm gear isn't some kind of nylon bushing that a rack slides back and forth on as the door/damper opens and closes, rotating the gear wheel to rotate the shaft of the position-sensing device.... A rack and pinion mechanism, rather than a worm mechanism....
Yes, worm gear was the wrong terminology. Apologies. The small cog engages with the teeth on vent opener - a metal door approx. 100x250mm that exposes or closes the shown vent.

Am not sure what the larger bolt is for but will check again.

The assumption is that the Carrier unit has some sort of circuit that opens and closes by controlling the rotation of the cog.

You <i>do</i> know what happens when you ass-u-me something.?.?.?

Look, I've been wrong before--and I'll be wrong several times in the future. It's just extremely difficult to understand how the three wires (which are connected to two wires, you said) can make a potentiometer or rheostat act like a motor and produce torque.

The markings on the black, round, motor-like device are too similar to those of a pot or rheostat--not a motor. Motors don't typically have nameplate data expressed in ohms; they usually have the voltage and/or frequency to be applied to the motor terminals and maybe something about which motor terminals do what. And, finally, the reference found to the Carrier part number just seems to be further evidence of this device not being a motor capable of producing torque ("lvps" may mean "low voltage position sensor"--just a Silly Wild-Arsed Guess on this).

You really, Really, REALLY need the schematic drawing(s) for this reefer container, mate! And, you also need to know that these reefer containers are basically commodity items, meaning they are subject to many, many different--but similar--configurations. They all provide the same functionality (refigeration), BUT the components used to do this can be nearly identical or they can be very different all while still providing the same functionality. AND, many times the technicians (if they're lucky enough to have had some electrical and refrigeration training) make modifications to the systems, and of course, those don't get made to any as-built drawings kept with or provided by the original equipment manufacturer.

In many parts of the world automobiles are exactly the same. There are subtle differences in the parts used for the same model and year, making buying spare or renewal parts difficult if not impossible sometimes. They all will get you to point B from point A--but they might have different front end axles or disc brake calipers or different radiators or even different transmissions (with the same drive ratios).

Reefer containers are no different--even when the core equipment is made by the same manufacturer. Some see duty in one part of the world, with one set of requirements, and some see duty in another part of the world with a different set of requirements, and some see duty in both parts of the world with a unique set of requirements that sacrifices extremes for part-time duty. It just depends.

But, assumptions--those can be a very bad thing. Best to keep an open mind. One can have tendencies and use past experiences and knowledge to formulate expectations or hypotheses, but reality can be a cruel teacher if one is too wedded to some idea or notion.

PLEASE write back to let us know what you find. On a side note, I don't think I really saw any damper door in the photo or the video. If you can post a better photo or photos or a better video that would help me better understand.

Keep an open mind--and be wary of assumptions. They can be a dangerous thing and lead you down the wrong path sometimes.
:) I could not agree with you more.

That said, without a schematic, and with serious doubts about what exactly I have, (other than the fact it serves as a potentiometer) am thinking my best way forward is to remove it and mount a stepper motor in its place that will perform the required function.

The ideal would be an integrated low speed (geared) stepper motor which can be say Modbus controlled, and recalls its state so I can request it to rotate in either direction to a previously calibrated setting.

Not sure if such a beast exists, but it really a simple servo, so there should be something out there.