Trane XL90 Thermostat problem


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Old 03-14-10, 11:53 AM
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Trane XL90 Thermostat problem

We have a Trane XL90 (TDX060R936V) gas furnace, no A/C. It was installed with a Honeywell T8624 D2004 2 stage thermostat.

Problem: Thermostat reads 66 degrees, but the indoor air temp is 62 degrees. The discrepancy is getting worse. I can keep increasing the settings to compensate, but is there a way to reset it or manually modify some hidden settings or am I looking at replacing it?

If I replace it, I would like to get a simple non-programmable t-stat. We have tried using the progam features, but they don't fit with our lifestyle.
Is there a Honeywell non-programmable t-stat that matches this furnace?

Thanks.
 
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Old 03-14-10, 12:11 PM
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Do you mean the set temp on the stat is 66, while the same stat's indoor temp reading is 62? Or do you mean your thermostat's indoor reading says 66, while some other thermometer in the house reads 62?

If it is the first sentence question, and the furnace is not calling for heat, then we have to know if you have a furnace problem rather than a stat problem. Because with that discrepency, it seems like it should be calling for heat unless you have it programmed wrong.

You have no manual overide for the time settings? You'd think you should have. Then you would know if it is a programmin issue(or stat malfunction in that regard), or perhaps a furnace malfunction issue.
 
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Old 03-14-10, 04:51 PM
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I would suppose that rather than having a thermostat that isn't working properly, it's a lot more likely that you have a furnace that is shutting off on a high temperature limit switch because of a plugged filter or some other air flow problem.


You need a multimeter that measures 24 VAC. Connect that up between the "C" and the "W1" terminals on your furnace. You should then have 24 VAC when the thermostat is calling for heat.

You can then determine if the thermostat is failing to turn on the furnace when it should be calling for heat, or whether the thermostat is calling for heat as it should but the furnace isn't turning on, or isn't staying on long enough to heat up the house.
 
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Old 03-14-10, 08:35 PM
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clarification

I set the temperature to 66 deg. The furnace runs until the display reads 66 deg and then shuts off. Everything seems to be running properly. But the air temperature is really 62 deg as measured by two different thermometers.

I found the installation guide on the net and discovered how to access the hidden settings including the one that allows the display to show temperatures that are higher than the air temperature. I checked this on my t-stat, but it was set to the factory default = the air temperature (no increase).
 
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Old 03-15-10, 10:37 AM
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Is the stat located at the return air, so that air is pulling through your stat?
You may need to seal the wiring behind your stat with some silicone.

Is the stat located in a location that would allow a supply air register to hit it?
You may need to adjust the louvers on your grill.

It appears that the cycles per hour is fixed at 6.
http://www.programmable-thermostat.c...8624manual.pdf
 
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Old 03-15-10, 04:49 PM
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On your last post, we now learned the stat or the furnace does not have any operational problem.

But NOW you never said where you are holding those other thermomenters. If you held them right next to the stat - then either the stat calibration or the two thermometers are off.

Are the two test thermometers mechanical, digital, or alcohol thermometers.

Where exactly in relation to the thermostat are you holding or placed the test thermometers? Same room as stat? Different rooms? Rooms that have register(s) only partially open or blocked?

For any meaningful help, you also need to be holding them up in the air the same height as what the stat is (generally about 5 feet off the floor.) If for example, you set the test thermometers on a lower end table.......maybe you WOULD get 62 down there, for example. Or if you were near a cold air return.
 
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Old 03-15-10, 10:00 PM
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The thermometers are both of the alcohol type and were hung right next to the furnace thermostat, and not touching the wall.

The thermostat is near a return air vent, but I have been watching the temperatures when the furnace is off for hours.
 
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Old 03-16-10, 04:25 PM
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Eirther you have to set your stat to 70 (so your room is really 66), and live with the inaccuracy - or buy another one, I guess.
 
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Old 03-17-10, 07:42 AM
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Thanks for the time and assistance.
We will just live with it for now.
 
 

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