You should verify that the thermostat is compatible with your system....definitely worth discussing with your AC professional.
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This link seems to show your XT80 has a 4-speed fan. That is not the same thing as a variable speed fan. Its likely just a constant speed unit and the installing contractor just picked the speed they assumed would work.
As others have mentioned, measuring for a 55 degree discharge air temp is the simplest way to get the fan speed dialed in but could still result in problems if your AC is not operating in spec. Being able to measure fan static pressure (to calculate CFM directly) and using a psychometric chart would be a big help, and refrigerant pressure is the gold standard.
This could also be a problem. There are no easy fixes to this one, but sometimes airflow adjustments can help.
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Certainly seems to be the case. I had looked a variable speed air-handler from Trane, so that was probably the XV80.
@Hal3, cancel your Amazon order. The XT80 is not Comfortlink compatible. For a start just rewire the blower to be one speed slower.
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Thanks for the prompt replies!
I didn't order the thermostat.
I will investigate using a lower speed.
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Start with measuring discharge air temp. I measured mine by drilling a small hole a couple feet downstream of the coil and using a stick- type thermometer. Something like this
Amazon thermometer is probably adequate. You'll need it to respond fairly quickly and wait for it to stabilize. Return air temp should match what your thermostat displays, but check it just to be sure. You can cover the holes with duct tape (the shiny silver stuff) when you're done. I should also note that my ducts are in my basement and NOT insulated... your situation may be different.
You should also check the capacity of your AC unit. This is usually on the data tag of your outside condensing unit and "coded" into the model number. It's usually (but not always) a 3-digit multiple of 12 (036, 048, 060, etc.). Along with your temperatures and some fancy math it can help you estimate airflow.
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I photographed the circuit board when I was in the attic.
I think this is what I need to adjust.
I'm not sure about that. So typically, installers only wire in two speeds for a multiple-speed fan. One speed to use during cooling and one during heating. When I changed my blower speed, I had to change the wiring to use the lowest speed.
What makes you think this is the fan speed adjustment? Do you have access to the installation manual?
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Here's an installation manual for the XT80 (hopefully your specific model is covered), and that there haven't been too many changes to the control board between model years.
The blower motor speed taps are described in "Table A" on Page 15. The dip switches that you linked to control the heat off and cool off blower delay (see Page 14).
I am searching the internet. I haven't found the instructions for setting the fan speed on the XT80.
I haven't found the instructions for setting the fan speed on the XT80.
Check the post above yours. I've linked to the manual, and indicated the specific page you need to look at. It isn't set by dip-switches. You have to use different motor taps for low, med-lo, med-hi, hi speeds - pretty much exactly what I did when I reduced the speed on my old system.
Edit: looking more closely, the manual I linked to matches your control board as best as I can tell.
For some reason the manual shows nearly every model using the high speed fan setting (BK/WH...black wire with white stripe) for cooling.
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I know - that is ridiculous.
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That - and the diagram on Page 15 of the manual I linked to (or the equivalent page of the manual you found).
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@Hal3, I know that houses are very different. My house used to be about 68-70% RH at 73F. After changing the speed tap for cooling to low (from high), it dropped to about 62-64% RH at the same temperature.
So you're on the right track, I think.
THat would give you low, not med-lo. (red is low from the manual). Be careful, that might make it too slow, and you risk the coils freezing.
Yes. I just edited.
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