Trane RTU problem

[Jshanl]

We have a customer that has a Trane YCD120 RTU that has been giving us fits. Back in Feb we got a no heat call,my guy found a bad CTI board,the actual problem was that resistor #15 on the CTI board was burned. He replaced the board and everything was ok. The unit ran fine until last week,then we got a no heat call. When my guy got there he found the same resistor on the CTI board burned up. He called Trane and explained the problem and he was told that there had to be a problem in either the tstat wiring or the thermostat and to replace both of them. On Thursday we ran a new stat wire,replaced the CTI board and in stalled a new stat. Well this morning we got the dreaded no heat call again. I have a guy on the way there right now to see what the problem is but I have a feeling that it is the same problem as before. Has anyone had any problems like this before.The full model is
YCD120B4H0BA
Serial # G07142587D
Thanks for any help

[Southern Mech]

I have tapped into my Trane portal, using the model and serial#, I have found no confidential service bulitin's or case scenario's. I would trouble shoot the low volt side of the RTU, contactors,relays and such, look for a coil going bad.

[Jshanl]

My guy got there this morning and found the combustion blower running but no flame.He looked at the board and the same resistor is burned.My man turned the unit off and went through all of the wiring connections and plugs thinking maybe there was something loose somewhere,he did not find anything out of the ordinary so he turned the disconnect back on to check voltages and amp draws and the unit started up properly and all the readings were ok. I called Trane to go through the situation and they told me that it could be the economizer plug causing the problem. Well this unit does not have an economizer so the Trane guy was stumped and said to change the main board. He also said that the resistor is probably not bad as he expects them to turn brown after they have run a while plus the unit would have not have started if it was bad. He was talking about a while meaning months not days.I'm going to get a new board and change it but I'm not too confident that this is going to fix the problem and I hate throwing parts at something.Any ideas?
Thanks

[Allen]

Hi Jshanl,
What is the gauge of the thermostat wire that has been run to the thermostat?
If it is 18 gauge, it is only good for 75 feet from the RTU. This can be verified in Trane bulletin MICRO-M-2D. The gauge of the thermostat wire is very important when using the CTI. If the run is too long it can cause the fuse on the UCP to blow.
Good Luck,
Allen

[hvac_two]

Need to know what type of stat you are using. If you are using a Lightstat there are some things you should know...The other step is to ensure your tech is properly trouble shooting the issue. Maybe send another guy/woman out as sometimes a second pair of eyes can see what someone else may have missed. Also I would remove the thermostat wiring and run the unit through the test sequence allowed by the voyager board. If that works out well you will want to make sure that the conventional t-stat wires are connected properly on the terminal strip. Also you can buy a Venstar CTI that will work on Trane Voyager.

My opinion on this is that someone has miswired at the terminal strip (THE WIRE CONNECTIONS ARE DIFFERENT THAN WHAT YOU WOULD USE FOR A DC CONTROLLER), or there is a short.
~~You also may want to install a DC sensor (BAYsensor) or DC thermostat and see if the problem goes away...If it does it IS a wiring problem that is causing the CTI setup not to work properly

[timebuilder]

Need to know what type of stat you are using. If you are using a Lightstat there are some things you should know...The other step is to ensure your tech is properly trouble shooting the issue. Maybe send another guy/woman out as sometimes a second pair of eyes can see what someone else may have missed. Also I would remove the thermostat wiring and run the unit through the test sequence allowed by the voyager board. If that works out well you will want to make sure that the conventional t-stat wires are connected properly on the terminal strip. Also you can buy a Venstar CTI that will work on Trane Voyager.

My opinion on this is that someone has miswired at the terminal strip (THE WIRE CONNECTIONS ARE DIFFERENT THAN WHAT YOU WOULD USE FOR A DC CONTROLLER), or there is a short.
~~You also may want to install a DC sensor (BAYsensor) or DC thermostat and see if the problem goes away...If it does it IS a wiring problem that is causing the CTI setup not to work properly.
Visit the .

Some good points are being raised here.

On some units, a Lightstat needs a resistor to function correctly. They come in the Lightstat package, in a small envelope.

The CTI board resistor issue points to high current. This can either be a miswiring as pointed out in the quote above, or a short somewhere that is allowing too much of a draw through the resistor, if it is in series with a thermostat wire. You can use an amp clamp to measure how much current is flowing from the unit and into the stat wiring to check that.

The CTI board comes with a door panel sticker for the mod, and the wiring should indeed be checked to assure that it is correct. There are many way to screw that up, so be aware.

After you use the Trane resident test sequence, use jumpers to see if the CTI is responding to the conventional inputs properly, using the wiring diagram to check as you go.

[supertek65]

I have had this same problem, but in cooling!
If I remember it was the bottom right hand side of the board , I am thinking relay number 8!
anyhow it turned out to be the contactor coil!

good lucK!

[just_opinion]

My guy got there this morning and found the combustion blower running but no flame.He looked at the board and the same resistor is burned.My man turned the unit off and went through all of the wiring connections and plugs thinking maybe there was something loose somewhere,he did not find anything out of the ordinary so he turned the disconnect back on to check voltages and amp draws and the unit started up properly and all the readings were ok. I called Trane to go through the situation and they told me that it could be the economizer plug causing the problem. Well this unit does not have an economizer so the Trane guy was stumped and said to change the main board. He also said that the resistor is probably not bad as he expects them to turn brown after they have run a while plus the unit would have not have started if it was bad. He was talking about a while meaning months not days.I'm going to get a new board and change it but I'm not too confident that this is going to fix the problem and I hate throwing parts at something.Any ideas?
Thanks

That CTI board will always has a brown-out resistor. So, your tech MAY mis-diagnosed there. I bet if you put all those old board back, they work fine. But I could be wrong on the ethernet-world.

The problem is with the unit and has nothing to do with controlling wires.

Check, gas pressure, induced pressure ... It is in there.

Damn those POS trane. All it can tell is "heat fail". WTF :gah: Flash back, flash back, Control yourself

[jayguy]

...Damn those POS trane. All it can tell is "heat fail". WTF :gah: Flash back, flash back, Control yourself

there's the j_o we all know!

[supertek65]

LOL!









there's the j_o we all know!

[Southern Mech]

I haveve suggested to troubleshoot the low volt circuit, I have seen 1 or 50 of these things.

any outcome yet?

[supertek65]

that is a cute little 5h avatar you got there SM!

[Southern Mech]

that is a cute little 5h avatar you got there SM!

That is at a plastic process plant I have under contract, they have 4 of them for comfort cooling, 225hp Carrier V-12's, we just put accumulators in this fall, the building is pnumatic and they don't know how to operate it. End result is 2 wiped out journals. 1 new compressor is already down a cylinder due to liquid. They just won't learn.

[Jshanl]

Thanks for all of the reply's. You are correct about the resistor being ok,my guy thought that because it was discolored that it was the problem and the first Trane tech rep did not tell us that it does get discolored after a while. The second Trane rep told us about the resistor and we checked everything he and all of you told us too. Upon finding everything checking out ok he told us to change the UCP board. Knock on wood but my guy changed the board yesterday and for the first time this week we did not get our morning no heat phone call. Looking at the back of the UCP board there seems to be an area that is discolored and this is where the wiring harness from the CTI board plugs in to the UCP board. My big worry now is was this the cause or a symptom of the real problem? Hopefully this was the cause,but I guess time will tell.

[hvac_two]

No problem.........these kinda of service calls are good for your service techs...Service techs will tend to get stale if they repeat the same old easy stuff every day.

~Like a good service challenge.

[just_opinion]

225hp Carrier V-12s'.

Wonder why 225 hp ? I hardly see 1 motor driving 2 of these 5H-120 or 5H-126. Like said - just wonder.

It normally takes 150 hp, which is plenty of horses

[Southern Mech]

Wonder why 225 hp ? I hardly see 1 motor driving 2 of these 5H-120 or 5H-126. Like said - just wonder.

It normally takes 150 hp, which is plenty of horses

sorry I ment 125hp.