Trane TCONT803 stat acting strange while calling for heat


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Old 11-15-14, 07:48 AM
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Trane TCONT803 stat acting strange while calling for heat

This past week when first calling for heat this fall, the stat is not working as expected. It will turn the unit on and then stop before it reaches the set temp.

After overnight set back to 60, it won't turn the unit on to get the temp up to 67 by 7AM. During the day, it is not maintaining the set temp during the programs.

Not sure how to troubleshoot this issue so any advice would be much appreciated.
 
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Old 11-15-14, 08:03 AM
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Do you have a gas furnace?
Any blinking trouble codes on the furnace (if you have a furnace)?
Is the air filter clean?
 
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Old 11-15-14, 08:29 AM
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Yes, it is a Trane 4YCY4030A1075AB electric/gas packaged unit. No blinking codes but I haven't checked the filter yet but I will.
 
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Old 11-15-14, 09:05 AM
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https://www.trane.com/content/dam/Tr...4_03012013.pdf

A dirty air filter could give you 4 flashes...
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Old 11-15-14, 11:31 AM
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I just checked the air filter and it is indeed pretty dirty. So even though there isn't an led error light blinking on the unit, this could still be the problem? How does a dirty air filter keep the unit from running to maintain the set temp? Should I run it without a filter until I can buy one Monday?

Thanks
 
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Old 11-17-14, 06:13 AM
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So I tried a new filter and the unit still was two degrees short of its set point this morning. Anything else to check? Thanks
 
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Old 11-17-14, 06:20 AM
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Here is a link to the installation manual. You might try adjusting function 680 to see if it corrects your issue:

http://www.denverwinair.com/literatu...tall_guide.pdf
 
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Old 11-17-14, 07:24 AM
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Thanks for the reply, I currently have installer option 680 set to 3.

It's really strange, the unit is able to maintain the set temp through all programs except the "Wake" set which is usually trying to recover from an overnight dip to 62-64 to 68. It seems to fall short by 2-3 degrees every morning.
 
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Old 11-17-14, 07:50 AM
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I believe that what Houston204 was hinting at in post #4 is that your furnace may be opening the high limit control causing the furnace to shutoff until the switch resets and begins the cycle again.
Since the high limit control is self-resetting you would need to observe the control board to see if the 4 flash code is presenting.
 
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Old 11-17-14, 10:55 AM
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When you say self-resetting do you mean a manual reset by me?
 
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Old 11-17-14, 11:12 AM
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No, when the high limit switch opens because of an over-temperature condition it shuts the gas valve off. The blower will continue to run to cool off the over-temp condition. Once the bi-metal limit switch cools off it will close the circuit and allow voltage to flow again and the ignition process will resume. This can happen without the homeowner even knowing it unless they observe the operation and see a flash code.
 
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Old 11-17-14, 11:15 AM
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Thanks for the replies! So, with that in mind a new air filter and adequate airflow should prevent the unit from shutting off when trying to recover from 63 to 68 at wake up. Right? This morning the same thing happened. Perhaps there's another reason why it shuts itself off?
 
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Old 11-17-14, 11:23 AM
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I would get a digital thermometer and check the rise in temperature across the unit while it is heating.

The unit nomenclature will list the rated heat rise.
If you are near or exceeding the maximum heat rise that coil may be dirtier than it looks or you may have a ductwork issue.
 
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Old 11-17-14, 11:52 AM
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I have scheduled a service tech to come Thursday. Hopefully will get a clear answer and resolution. I will report back with what he finds.
 
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Old 11-17-14, 04:45 PM
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The external static pressure and delta t would be some valuable information.
 
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Old 11-20-14, 08:47 AM
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Appointment has been rescheduled for tomorrow morning... I'll post an update tomorrow.
 
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Old 11-21-14, 09:19 AM
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So far, the tech has found the LED blinking 4 times. Replaced the high limit sensor and the problem persists.
 
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Old 11-21-14, 09:23 AM
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Unit has always run seemingly okay with a MERV10 20x25x4 inline filter. Tech is suspecting not enough airflow to prevent the unit from overheating. All vents are open so I'm not sure right now.
 
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Old 11-21-14, 10:09 AM
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The tech needs to check the temperature rise to ensure it is within limits. Also, if you have an a/c coil installed at the furnace it needs to be inspected to ensure it is not clogged. A dirty/clogged coil is just like having a dirty/clogged air filter and can severly restrict air flow causing overheating.. The fact that you stated you found the air filter "pretty dirty", there is a good chance the coil is pretty dirty.
 
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Old 11-21-14, 11:11 AM
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As a test we had the unit reach a set temp of 72 from 66 without a filter in place. It reached it without shutting down prematurely within about 45 minutes. Tech is thinking that MERV10 and certainly MERV12 is restricting airflow too much and causing the unit to overheat and shut down.

I think I'll take your advice and have the unit inspected and cleaned as needed. Thanks!
 
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Old 11-22-14, 07:58 AM
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Installed MERV7 filter and the unit was able to recover from an overnight low temp of 62 to a wake set temp of 68 without falling short. Seems to confirm the airflow issue.
 
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Old 11-22-14, 11:24 AM
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It is too bad that the tech didn't measure the external static pressure.

It would easily show if an air restriction is present on the return air duct, the supply air ducting, or both.

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I wonder how much air the board thinks it is moving?

A measurement of the heat rise across the unit would have also been a great idea.
This information can be compared to the rated heat rise on the package unit nomenclature.

A limit switch trip is rarely caused by a faulty limit.

http://www.climatesolutionsinc.com/c...CY4-Manual.pdf
 
 

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