Trane UCP troubleshooting

[JohnBuckingham]

I had a Trane YCH unit where nothing was running. Power was on, fuses OK, no obvious problems. Following the instructions in the Voyager Microcontrols manual, I checked the UCP LED (it was on), then checked LTB terminals 6-9. There was OvDC, so I installed a new UCP and the unit started.

Being curious, I checked LTB 6-9 again, and the voltage is still 0. Normal should be 32vDC.

Am I doing something wrong, or is there still a problem with the unit?

Thanks,
John

[vbhvac]

Stupid question - You cycled the power before replacing the board - right?

[hvacman77]

like vbhvac said...did you shut down and power up the unit...sounds stupid but it matters..there are a few things that just lock out that UCP, and you will not measure I do beleive any dc volts at those terminals indirectly. What year is the unit?

[JohnBuckingham]

Yes, I shut it down and restarted it a few times before I replaced the board. The unit was manufactured 09/94.

It's been working fine for several days with the new board, but LTB 6-9 still doesn't have 32vdc like the book says it should.

[300 Win Mag]

If the unit has an economizer, unplug it and recycle the power. Let me know what you find.

[JohnBuckingham]

No economizer, it's connected to a Barber Colman system.