Vari-Trane VAV noise

[tchntch]

I recently took over a building with about 30 these VAV boxes. They were built in 1995 and are what Trane refers to as analog units and use 3k zone sensors rather than 10k. As the air valve (damper) makes frequent, minor open and close adjustments it makes a very audible growling noise. A major temp change will cause a long r-r-r-r-r as it goes to a new position. All of these boxes seem to do it.

I have had several talks with Trane tech support about it. The local Trane supplier has had me replace the acuator motor, large plastic gear and bushings with hardly any improvement. Trane commercial tech support has no other answers and says they will call me back but don't. They always seem to be uncooperative if you are not a Trane dealer.

From what I see in the building there have been numerous attempts to reduce the noise: many parts changes and large batts of insulation on the ceiling tiles under the boxes. They may have been noisy from day one and Trane doesn't want to own up. There is a new owner of the building and he has no idea what has been done in the past.

Has anyone run into this and have any solutions?

[ascj]

You rebuilt the VAV's and they are still making the noise?

Replacing the backplate assembly should have solved the noise issue. From my experience with the grinding noise, it has always been the plastic gear's threads wearing out.

[tchntch]

Thanks for the reply.
It is nice to know that it is possible to quiet them down and I'm not beating a dead horse. I just have to figure out what I haven't done right. I guess I should try another plastic gear.

[ascj]

Thanks for the reply.
It is nice to know that it is possible to quiet them down and I'm not beating a dead horse. I just have to figure out what I haven't done right. I guess I should try another plastic gear.

I normally order the backplate assembly, motor, and cap. The backplate assembly will include the metal backplate, new main gear, stop switches, damper rod, and mounting rod springs.

[alcomech]

I have repaired many of these boxes as well and have not had any which cause abnormal noise.
Did you provide Trane the serial number of the VariTrane VAV box so that the correct parts can be obtained.

It sound like you have the the older series VAV box and the older series UCM
Board No. 6400-030-01

Are you certain that you have installed the correct air valve motor either 300 RPM or 600 RPM. How about the gears which are available in different size, color and also air valve threaded rod size's are different in diameter which is based on series or Serial No.

Up to 10" air valve use's the following:
PN: MOTO8839 Small Gear
300 RPM 24 VAC

12" air valve and larger
Varitrane motor:
PN: MOTO8840 Large Gear
600 RPM


VariTrane Gear
GER00135 Red Drive Gear
GER00137 White Drive Gear Small

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Trouble shooting is not part of the repair....understand the symptoms and you will find a solution.

[tchntch]

Thanks Alcomech.

When you refer to no "abnormal noise" do you mean to say that there will be some noise? All the boxes that I have found make this noise. It is audible below the boxes which are about 10 feet above the floor with a t-bar ceiling beneath them. Most of the tenants seem to have learned to ignore it. I just wonder if it is "normal" or if it should be audible in the conditioned space.

So far I have only attempted to correct it on one box. Trane parts gave me the motor, gear and bushings based on the serial number. They seemed to know right away what I needed. The motor was the MOT08840 and the large white gear was GER00139. They looked identical to the originals and did not make much of an improvement.

[alcomech]

Most all Varitrane VAV's will make some kind of noise when the air valve move's to a new position. The normal sound is the movement of the motor against the gear and the positioning of the gear on the threaded rod.

It is not required, but a few drops of oil on the threaded rod will not hurt and will make for easier gear positioning.

I have seen it many times when the UCM board is not calibrated correctly and it will hunt for a correct position. When this happens it will create a continuous nuisance sound, or as you explained a growl. It is very easy to identify this by the constant flicker of light between the red and green led which indicate opening and closing.

If this is the case you will need to calibrate the UCM and set minimum and maximum air flow set points.


Null Range Pot R-8
Note: Pot calibration-
Sets dead band / null range but normally does not require adjustment on existing systems. However you will need to identify if it's voltage out-put is correct per Installation Operation Manual.

Set Cool Minimum first.

Minimum and maximum air flow:
Calibration: Set Cool Min First
Pot R69 (B) = Cool Min Flow
Pot R68 (A)= Heat Min Flow
Pot R67 = Max Flow
CCW lowers CFM
CW increase CFM

Let me know if you need more accurate info as this not complete.

Note: Maximum flow must be greater than or equal to minimum flow set point.

________________________________________
Trouble shooting is not part of the repair.........understand the symptoms and you will find a solution.

[tchntch]

Thanks again Alcomech,

I have been using the IOM manual to try to calibrate the unit. Im not sure I have been doing it well. It would be better if it didn't do the constant back and forth search for position. I'll give it another try. Then I'll try ascj's backplate idea.

Thanks to both of you for the help.

[alcomech]

If you have already calibrated the UCM exactly like the IOM indicates which sets minimum and maximum flow, as well as minimum for cool and the UCM continues to hunt for position then its clear that you need to verify the operation of POT R-8 which controls the null range.

This Pot works in conjunction with the thermostat and controls signal out put voltage. There are times when this POT has a degraded performance and accuracy is no longer consistent and voltage signal does not correspond to thermostat set point. If that's the case than you have no choice but to install a new UCM.

The part number for a new board is BRD00605. Expect to pay way over a couple hundred bucks on this one.
Thermostat is PN: SENO1234 3K ohm

________________________________________
Trouble shooting is not part of the repair.........understand the symptoms and you will find a solution.

[ascj]

You did verify that both outputs are opening and closing properly.......nothing like one output stuck closed, will cause it to hunt like crazy and make quite abit of noise.

What's the main AHU doing.....those boxes will be all over the place with high primary air static?

[alcomech]

ascj you have a very good point as far as the static goes. This VAV with this type of air valve is capable of handling slightly over three inches of static and it is recommended to not be less than 1".

[tchntch]

Thanks to both of you for the input. I've got plenty to work with when I get back there.