Varitrane heat problem

[SomeOldGuy]

Hi
Single duct electric heat VAV. The heat cycles on and off. The setup is identical to others that do not show the problem. Board # is x13690252-07 comm4, Voltage, flow, safteties etc all ok. Any clues?
I verified it is setup for 3 stage electric and not pwm.

[deux]

Can the discharge air sensor be moved? Just a dumb thought. I had an issue once with a sensor. Moved it a bit and all was well. It was almost like the hot air was not mixing right away with the cool air. Like it was flowing in a band for a bit.

[SomeOldGuy]

There are no discharge air sensors. On any of them.

[deux]

Huh, really? I gotta find a manuel. Maybe mine was an add on..... Are you suppose to have one? Maybe your missing a fixed resistor? Huh, our Canadian mods are most likely made different.

[Phisher]

Are you sure it's not cycling on the high limit?

[SomeOldGuy]

Yes I am sure it is not cycling on high limit. The power/signal stops at the board itself. There are no fixed resistors either. I thought of that. Worked before. Dont now. I go back when I have a clue. Or a new board to try. Hate doing that really.

[harrelson]

is the min heat cfm being meet ?

[Trane Guy LI]

Is the vav in heat or cool mode ? is it on a Bas like summit. In summit there is a min. heat cfm set point that has to be set high enough to keep the limit from tripping.

[ISAMemphis]

If the safeties are all made and the unit is making it's min heating cfm then it is more than likely the board. If you don't want to be a "parts changer" try swapping it with a board that you know works. My guess is the board. Good luck.

[mallron]

Where are you measuring voltage when you say the signal/power stops at the board? There should always be 24v present at the contactor(s) if the safties are made.

[SomeOldGuy]

Hi guys
Sorry for the delayed response. The minimum cfm idea is not it since I tried using a higher minimum and it did not work. It is on a summit BCU. I dont recall the terminal numbers but there is one slightly offset to the right that I will call common to the heat contactor. And then three more terminals for the three stages. When between the common and stage 1 or two becomes live the contactor/s pulls in. When I read 0 vac the contactor drops out. That is what I meant earlier by at the board. So I guess I am at the change the board stage.

[SomeOldGuy]

Is the vav in heat or cool mode ? is it on a Bas like summit. In summit there is a min. heat cfm set point that has to be set high enough to keep the limit from tripping.

Heat mode, Room temp 67, Summit BCU.