Trane parallel vav box with ucm control board

[CommtechinVA]

Having issues with a couple of these boxes. Can't seem to get the vavs to respond properly to a change at the zone sensor or the tracer touchscreen. I have replaced the pressure transducer and cleaned the pickup rings. If I drive the damper from the tracer panel, the vav starts opening for a minute or so and then stops. I have checked the end switches on the damper assembly. I'm about to change the board as I can find nothing else that canned wrong. Any help would be appreciated.

[hvac69]

Have you tried a force open or just force max flow? Are you losing power at the terminals that drive the motor, common to cw or common to ccw? If you do a force open it will drive the actuator for the set actuator drive time and the end switch will stop it should the air valve get to the end before the time expires. I cant remember off the top of my head if there is a actuator drive time setting or if its automatically set when the box type is set.

[gwoner]

Have you tried to calibrate the boxes from Tracer? Also is this a start up or existing account?

[Allen]

Hi CommtechinVA,
There is nothing wrong with the UCM.

If the VAVs are connected to Summit, Summit is stopping your override, and returning it to normal operation. Or what it perceives as normal.

If your customer has a work station, go into and check the setup of the UCM at the problem address. Check the Flow Control setting, normally set to Auto.
Check the Zone Sensor temperature, to see if somebody has put offset into the sensor.

Let us know.

Good Luck.
Allen

[ascj]

If I drive the damper from the tracer panel, the vav starts opening for a minute or so and then stops. I have checked the end switches on the damper assembly.

Big question........is the damper losing the 24v to drive the damper or is the damper getting the 24v and not moving anymore?

[CommtechinVA]

There is no work station, just a tracer touchscreen. When I force the damper open, it starts to open and then stops after 30 seconds or so. Ive had issues similar to this at another site and was able to calibrate the Box thru the workstation and it commenced to work. Is there a way to calibrate from the touchscreen? By the way, it is an existing account.

[CommtechinVA]

As I understand these systems, they have 24 volts at the damper all the time and the voltage path is completed thru the common side. These are older vavs with the round damper.

[ascj]

As I understand these systems, they have 24 volts at the damper all the time and the voltage path is completed thru the common side. These are older vavs with the round damper.

Voltage is not completed on the common side. They have Triacs. With the three wire plug connected....you with read 24v on red for a call to close and 24v on black to open. Don't be fooled by the 30v on the opposite(non calling) term.....that is just caused by the motor and capacitor.

The dampers are notorious for stripped out splines and worn spacers. I find more problems mechanically then controls.

[CommtechinVA]

My bad, I believe I was wrong on the way these dampers work.
I believe that power comes thru on the common(blue) and then the path
Is completed either thru the cw or ccw.

[CommtechinVA]

Ascj, I realized that I spoke wrong , and you have confirmed my understanding. Mechanically, there is no problems on this one. The gears are fine. It just doesn't want to act right.