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Old 07-28-2011, 10:13 PM   #1
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need help with new Trane system


At the end of summer last year I had my 16 yr old air conditioner (2ton 10 seer American Standard) and gas furnace replaced with a 2.5 ton Trane XL15I heat pump, 3 ton coil, xv80 variable speed gas furnace and Trane clean effects.

I had a service call today because I don't feel the air although cold enough is as comfortable. I feel that humidity is not being sufficiently removed. House is 1300 square feet, tightly sealed with very energy efficeint windows and doors. My suspicion is that I should have continued with a 2 ton system but got upgraded to a 2.5 system where the 2 ton was more the correct size. I find myself lowering the temperature to 70-71 to get similar comfort to 74-75 on the old system.

I explained this to the tech today (from the company that installed the sytem). He made one change that he thought may help and that was to correctly set the dip switch on the coil for a 2.5 ton air conditioner. It had been incorrectly set for a 3 ton outside unit. I am still evaluating if that is going to help. Today was a low humidity day.

I also asked that he increase the fan speed in between air conditioning cycles. It now runs at such a low speed you can barely tell it is on. Since having the new system the air in the house always feels stale. I have lived here 12 years and didn't notice any issues with the previous system. He is going to look at how he can increase the fan speed and didn't know if it was possible. Is it? My thermostat is a programmable Trane TCONT800.

Any suggestions on getting lower humidity without lowering the temperature? Can the fan speed be adjusted when just the fan is on? thanks in advance for any help!

edit: couple of more items...house sits on a slab, furnace/coil in an attic in unconditioned space (same as old), no leaky ducts

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Last edited by supermaxhd; 07-28-2011 at 10:41 PM.
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Old 07-29-2011, 06:52 AM   #2
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most of the higher end variable speed units have dip switch adj for the low speed. usually +- 10% which is not huge and some can go more than that. Carrier is using 350 cfm/ton instead of the old school 400 cfm/ton and with a TX valve and variable speed fan that is safe to do (w/o those 2 features it is not safe to do, coil may freezeup and damage the compressor). subcooling needs to be carefully checked if doing that. will definitely improve your dehumidifying.

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Old 07-29-2011, 12:29 PM   #3
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Originally Posted by yuri View Post
most of the higher end variable speed units have dip switch adj for the low speed. usually +- 10% which is not huge and some can go more than that. Carrier is using 350 cfm/ton instead of the old school 400 cfm/ton and with a TX valve and variable speed fan that is safe to do (w/o those 2 features it is not safe to do, coil may freezeup and damage the compressor). subcooling needs to be carefully checked if doing that. will definitely improve your dehumidifying.
So for lower humidity I need to ask my HVAC company to see if they can lower the speed further. I would also like for the fan in fan only mode to push more air as it hardly does anything now. Is that possible with my system? Would another thermostat give me better control and if so what model? thanks for the help!
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Old 07-29-2011, 06:10 PM   #4
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need help with new Trane system


It is designed to barely move the air in fan on mode. This is for efficiency and also to lower noise and because that is all the more that is needed without a call for heat or cool. I would look at a vision Pro IAQ stat that can lower the blower speed with the air conditioning running to meet the set humidity level. This is what I use in my home.
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Old 07-29-2011, 06:48 PM   #5
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Very few people request a lot of air moving on low speed so they don't build that feature into the boards. On most of my average size Lennox 3 ton blowers the low speed is about 450 cfm and can be adjusted +- 10 to 15%. Not sure how elaborate the adjustment range is for your Trane and I don't have an install manual for it or specs. The installer should be able to get that info from Trane or the install manual and set you up properly. Less than 10% of the techs that I run into know how to do those fine adjustments or have the training or give a dam*n so it can be hard to get it done.
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Old 07-29-2011, 08:41 PM   #6
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You want them to slow the lower to 350 CFM per ton. And turn the fan to auto. running the fan continuous causes higher humidity. Set the thermostat fan switch to circ.

And yes, you should have stayed with 2 tons.

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