Trane UCP/ TCI-3 problem

[mrmike]

Hello all, I am having a problem with a Trane RTU, I hope someone here can help me since Trane tech support won't return my calls.

Model #YCD120B3HCEB
Serial # P47100404D

Ok, here it is. My orig service call was no cooling for the unit, I checked the Tracker control board and it told me that all 9 UCM's on this unit were not responding. I checked for control power at each of the UCM's and at the main Controller, all seemed ok there. I next moved to the rtu and found one of the resistors (91ohm R-45) was burned on the TCI-3 board. I checked the main UCP for any issues, none found. I ordered a new comm. board, returned and installed. As soon as I applied power to the unit, that same resistor on the TCI-3 board started smoking. I traced out the back side of the board and that resistor is connected to pin 6 of the 7 pin wire harness from the main UCP.
Does anyone know what the pin assignments are for the TCI-3 plug? This will get me pointed in the right direction and at least give me a starting point to begin troubleshooting

Thanks in advance

[heatingman]

I looked up the units schematic, and all it says it that the j6 plug interfaces to the tci board, to enable comm link control. There is no internal breakdown to what its function is. Two things. One the ucp board is bad, something shorted internally, or your comm link is shorted. You said that 9 units where out of communication, so I would look to that as the culprit. If it is the ucp, all those wires in the j6 terminal, are internal to the ucp, so you dont have to worry about the exact function.

[jayguy]

I traced out the back side of the board and that resistor is connected to pin 6 of the 7 pin wire harness from the main UCP.


on the TCI-3 board, connector J1, pin 6 is a 32 VDC input FROM the UCP. there is most likely a short. Connector TB2, pin 2 is an output to the "High Temp Switches if present". hook up a new TCI-3 board without any other inputs or outputs (or not at all and get it running just to prove there isn't anything else wrong with the RTU itself). then look for your short.

good luck.

[mrmike]

I dont have any high temp switch hooked up to the board, and as far as I know, the comm loop that connects to tb-1 i believe, is just a signal, no voltage. Should I look at the fan and economizer circuts first, seeing that they are the first things to initialize upon startup?

[jayguy]

like i said before...do not install the TCI-3 board. power up the rtu and check the outputs from the main UCP board. check for all of your short circuits. run the unit in test mode and make sure that all of the functions of the unit work and work well. if they do not, it has nothing to do with the TCI-3 board (since it is not hooked up) and you can make your repairs. then hook up the TCI-3 board. if, during the test mode, you find everything working, then the problem is not with the unit. look for other issues that are hooked up to the TCI-3 board.

pin outs for the UCP:
pins voltage description
J6-1 24 VAC Output TCI Power Supply for High Temp. Switch Input
J6-2 32 VDC Output Output to TCI Power Supply
J6-3 5 VDC Input TCI Installed, read unit address digital input
J6-4 5 VDC Output Transmit Data, Binary Output to TCI
J6-5 5 VDC Output Transmit Enable, Binary Output to TCI
J6-6 32 VDC O/I (Pulsing) Output to LTB-12, Receive data line for programmable ZSM or TCI if installed
J6-7 *Common Digital Common to LTB-11 for programmable ZSM & TCI

good luck.

[Knobber]

I dont have any high temp switch hooked up to the board, and as far as I know, the comm loop that connects to tb-1 i believe, is just a signal, no voltage. Should I look at the fan and economizer circuts first, seeing that they are the first things to initialize upon startup?

Please provide us with information on all of the field wiring hooked up to the unit. On the TCI-3 you should only have 1 or 2 cables terminated to TB-1 and possibly some wiring terminated to TB-2. I am curious if you have anything terminated to TB-2. TB-2 is designated as a high-temp input but is commonly used for any device that needs to shut the unit down.

The only other field wiring should be from the zone sensor (2 or 3 wires) that is terminated at the TB near the upper right corner of the control panel.

Have you tried disconnecting the comm wiring from the unit with the bad TCI-3, wire nutting it together, and then see if you can then communicate with the other 8 units??

Let us know.

Knobber