Trane XV90 comes on randomly--furnace repair challenge of the day!

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Old 11-26-11, 02:26 PM
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Trane XV90 comes on randomly--furnace repair challenge of the day!

My Trane XV 90 was installed in 2005 and is connected to a Honeywell electronic air filter system. The unit has worked perfectly until the spring of 2011. We'll get up in the morning and turn the thermostat up, and sometimes the furnace will come on and sometimes it won't. I have a Honeywell thermostat that also controls our A/C. The longest the furnace has stayed off so far is 3 days, but in the past month the normal duration of it being off is only part of one day. I swapped out the old thermostat for a new one while the furnace was NOT working and the new thermostat made no difference. The furnace still did not work with the new thermostat. So I took the new thermostat back and reinstalled the old one, which was also new in 2005.

I counted the green light blinks on the furnace board and it blinks 21 greens for every one red. According to the furnace manual, this is normal. The breaker to the furnace is on and normal. I can operate the furnace fan from the thermostat with no problem. I can operate the A/C from the thermostat no problem. Currently, we are in an OFF mode for the furnace and this is the third day of non-operation. I have disabled the programming mode on the thermostat to make sure unwanted programming is not turning the furnace off. I have had the thermostat in System Heat On mode. The thermostat appears to click on and off normally when I raise and lower the temp setting.
When the furnace DOES come on--which can be anytime--it seems to operate normally until the next time it decides to quit. Sometimes it will quit before we turn the thermostat down for the night. Other times it just doesn't go on when we turn the thermostat up in the morning.

We have left the house when the furnace was down (off) and when we got back home later that day, the furnace was running. Several times when it has started back up from being broken, it has heated the house to 2-3 degrees warmer than we had the thermostat set for. But after the initial return to operation, this temperature issue does not occur as long as the furnace continues to operate.

I have been keeping a log of when it does and doesn't operate over the last few weeks. The issue appears random. During the first week of November, the heater was off for 3 days. It came back on for part of the day 11/6. On 11/7 it came on and worked fine for a week. On 11/13 it didn't come on until 9:15pm. On 11/14 it came on normally. On 11/20 the heat went off at about 10pm. On 11/21 it came on at 8:30pm. On 11/24 the furnace would not come on and has been off since. Today is 11/26. The green light is still blinking about once per second to every 1 red blink. How come the lights say all is ok when the furnace is inoperable??

Back in October, I had a service guy come out from the same company that installed the furnace. It was a diagnosis call but when he was done he was still not sure what the problem was. The disadvantage for him was that the furnace happened to be running correctly when he was here. His best guess was a solder joint problem with the system board. He quoted me $1300 to replace the board with a new kit they now use. I checked with a do it yourself furnace place here in town and they said the kit alone was $850. I did not have the board kit installed because the company would not assure me that the work would fix the problem.

Our outside temperatures have ranged from the high 30's to the mid-50's over the past month. The furnace is located in the garage. The house is one level and is a duct system where air flow is from the top down.

Please give feedback in layman's terms as I am not an HVAC person. I CAN follow instructions though! Any help fixing this issue would be greatly appreciated! Thank you in advance!

Scott
 
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Old 11-26-11, 02:40 PM
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A furnace goers through a sequence of events in order to produce heat.

You need to take the front cover off the furnace and carefully observe and describe the sequence of events you see happening, in the order that they happen. Observe the furnace when it's working properly and again when it isn't. You will probably observe that the furnace stops some place in that sequence when it isn't working.

Report what you observe here.
 
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Old 11-26-11, 03:27 PM
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I woulda guessed the board as well, but I am at a loss for what kit they are referring to, ive never heard of a kit having to be installed with the board, oh unless you have a variable speed motor.
if not the board i would guess it would be a red to white short of some kind because apparently your furnace only acts funny in heat, which leads me to believe that the red and white wires going from the circuit board to the tstat must be touching each other. most likely location would be at the circuit board. red and white touching(bare wires) would turn the system on just like the tstat.
 
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Old 11-27-11, 08:33 PM
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Thanks for the replies, which I appreciate. Unfortunately, the furnace hasn't been operating of late so I haven't been able to observe it running. From observing it in the past, I mainly can HEAR differences, like the pilot light lighting and the fan running. The LED blinks the same whether running or not. Can you give me an example of what I might observe and the differences in the on and off states?

The heater did come on tonight at about 5:30 but only my son was home. By the time we got home at 8pm, the furnace was inoperable again.

The company (Trane) apparently went with a different supplier for some of their parts and now when you want to replace the board, they make you upgrade to this new board that comes with an inducer motor and wiring harness. I'll check the red and white wires and make sure they are not shorting.

Thanks again for your replies!
 
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Old 11-28-11, 03:54 PM
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Standby = slow flash
Call for heat = fast flash


yes, it is a kit. It upgrades your furnace to the current standards and gets rid of the ECM 1 inducer and replaces it with a 3 phase inducer. the kit includes a board, wiring harness and inducer. The kits take about 2 - 2 1/2 hours for a tech to install if it is their first one. Otherwise I've installed them in about 45 min.

Best thing to do is to remove the thermostat wiring from the control board. (take a picture or write down which wire went where) Then jumper W1 to R and see what happens, if it comes on every time then it is most likely the stat or wiring, but if it does not come on then it is likely the board.
 
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Old 11-29-11, 12:57 AM
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Earlier, I tried what you suggested, taking the wires off and jumping W1 to R. Nothing happened so it may be the board.

By the way, the furnace just came on at 12:40am on 11/29. Who knows for how long! It has a mind of its own it seems!

I looked at the board while it was running and the green and red lights that you can see thru the peep hole were now: green blinking twice as fast as when the furnace is off, 42 times before a single red blink (instead of 21 green blinks when ON). There is also a green light at the bottom right corner of the board that now blinks 10 times then switches to a steady light for 10 seconds, then goes back to 10 blinks, 10 seconds steady, etc. This corner light usually just flashes at a high rate of speed when the furnace is off. This is all I can observe about the furnace while it is running. The fan is on high speed and it is putting out great heat. But I doubt it will be for long. I'll need to turn it off soon and it likely won't start up tomorrow morning.
 
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Old 11-29-11, 03:41 AM
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you need a new board. Some shops still have the old board available. I know ours has a couple on hand before we start using the kits. On your current board should be a CNT***** number. try doing a Google search for that. That would be much less than a new board, but if the inducer decides to go sometime after the board was replaced then the board was a waste because both could have been done with a kit.

btw, lower led is cfm output.
 
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