Trane VAV Boxes

[apprentice3]

i work on alot of trane vav boxes in office buildings, they are the ones with a board transducer actuator inside duct to open and close damper. i can get the model numbers if that will help, but i have questions about the transducer, usually if the system wont respond and the red light meaning closing stays on it is either the stat or the transducer, and i dont like being a parts changer and trying one then the other to get it fixed, can anyone tell me how to diagonose these two parts. I have read about somethings about these boxes but trane never really gives you any literature, but they mention null voltage and min and max air flow, which are adjustable one board, but i was wondering if there is any voltages i can take to see if the stat is bad or the transducer

[chillerout1]

if it is the model that uses a zone sensor module to communicate with board get the soft ware from trane (e-ware) and you can dirve damper open and closed with laptop plugged into zsm. sounds like the one you have may be the one that uses plastic drive gears inside and they do strip teeth off but are easily replaced if pipe fitters didnt put sprinklerhead directly under access panel of unit.

[apprentice3]

im not sure if you can hook a laptop to it but yes it has a plastic gear that the actuator drives the air valve (damper) open and closed. It has the stat that has 3 wires hooked from the stat to the board plus it has a 24 volt supply to power the board, and what i am basically asking is how can you tell if the stat or the transducer is bad on these boxes, because they both do the same thing when they are bad, the led will just stay one color and you cant control the box to open or close, so either you replace the stat and it lets you tell it to open or close or you replace the transducer and it will fix it, but i would like to know a way to check the stat and the tranducer, and you cant check the stat by jumpering things out because i have heard it will come back and burn up the board.

[core]

What is the M# of the box?
I think Trane makes 2 types a VaraTrac and a VaraTrane.

If I remember correctly the 3 wire tstat is a resistive output and Trane makes a chart where its output can be checked based on setpoint.

Same goes for the room sensor which I believe is a 10K ohm @ 25 Deg. C.
I have some stuff I’ll take a look for you.

Core

[iamrichard]

generally speaking (not sure exactly about trane) but most transducers work on 4 to 20 milliamp signal back to the controller (or in Tranes case a board). This 4 to 20 milliamp is matched to the cfms in the program. Example: if you are at 0 cfms your signal back to the board will be 4 milliamps. If max cfms for that transducer is 500 cfms then you will get 20 milliamps at 500 cfms. One wire feeds a voltage (usually 24 vdc)to the transducer and the other wire feeds the milliamp signal back to the input on the controller or board.

Stats??? you have to identify the wires from the technical documents and remember not all stats are fed with voltage.

Richard
http://highperformancehvac.com

[apprentice3]

It is a vari Trane and the model starts with a vccd, i will have to go to the truck later on and get the rest of the model. I am aware of how the transducer works but just dont know how to tell if it is bad or the stat, usually have same symtoms

[koolitman]

ok it's been a few years but if I remember right to check the transducer
pull the high and low tubes off and take a multimeter and check for 1 volt at 0 pressure differance across sensor

I believe this is with the center wire and one of the outside wires leave, the sensor in place, wired up, and powered up. check a good one first to compare readings.

the tstat is 10,000 ohms at 72 degrees I believe check it with an ohm meter. good luck

[apprentice3]

thanks ill give that a shot