Here’s the wiring and dip switches. I would like to also see if I can take advantage of the comfort R by replacing the Tstat with an xl850 which supports it. The outside coil unit says comfort coil 🤷🏻‍♂️

AC - 4A7A7024A1000BA
Furnace - AUD2B080A9V3VBB
Coil - 4TXCB004DS3HCAA

 

Was the size of the equipment changed?
Was the furnace replaced at same time or just a/c? Furnace is an under model so would have had to been old stock.


Do not confuse efficiency with capacity, efficiency has nothing to do with how quickly a system cools beyond problems caused by worn out compressors and refrigerant leaks which also cut efficiency.
A higher SEER rating unit of same tonnage will have same runtimes and the goal in sizing is to actually maximize runtimes while still having enough capacity to maintain setpoint in extremes.

**
To answer your wiring questions...

Second stage heat can work without W1 connected and on that furnace a W1 to W2 jumper instead. When both W1 and W2 are energized in same instance, it turns on a 10 minute time delay and upstages to high after only 10 minutes.
It works, but since second stage heat is rarely needed to maintain setpoint, it causes a lot of unecessary use of high heat, upstaging and then having the thermostat shut the furnace down very shortly after that.
It far better to have W2 wired in to the thermostat so that you get long gentle heating cycles on low, and when it kicks into high the thermostat has the ability to drop it back down to low in the same heating cycle.

To need an 80 000 btu furnace like what you have, but only have a 2 ton cooling load -> you're talking a poorly insulated house or a place with extremely cold winters.
Needless to say that for most spaces that only need 2 ton of cooling, 80k furnace is oversized and could probably outright disable high heat removing the jumper and never be short of heat.

For air conditioning wiring,
Wrong - see tinkermans's post... yes Y1 and Y2 need to be wired to furnace and outdoor unit - it is essential for getting the blower speeds right on a 2-stage a/c. When the a/c is running on low, the indoor fan speed should be lower too.
You should check outdoor unit and see if Y2 is connected there, because they may have short-changed you not wanting to run new low voltage cables.
With the same a/c tonnage, the cycles should be longer going to a 2-stage.

Another potential cause of high humidity is not setting the blower speeds properly.
Most 80k 80% furnaces come with a blower rated and factory set for a 3 ton a/c.
The blower airflow setting must be reduced to about 800 cubic feet per minute for a 2 ton a/c, and automatically runs at 60 to 70% of that on low.

You'll need to go back to the contractor and get the a/c wiring corrected and blower speeds checked/adjusted if needed.
If the indoor blower speeds were not set correctly, impossible for them to have set the refrigerant charge correctly -> so the charge should be checked too.

 

The units sizing didn’t change nor did the SEER. The new downstairs units are working great and cooling the house efficiently. The older units I had (18 years) ran all the time)leaky coils that we had to charge yearly for the last 5-7 years.

This is the only thing that changed and made me start digging into the upstairs unit that was changed in 2020. Now that the downstairs is working properly with the new units, is it exposing issues upstairs… either that unit, the settings, etc…

something is now causing a humidity issue I never had before

Complete units AC/furnace.

 

To clarify on the W1 wire is connected, but not W2. I do not see a jumper… so im assuming I’ll only get stage 1 heat?

I live in Texas, we have limited cold spells, so AC is a bigger issue here than heat usually. In fact, I would argue we don’t run the heat upstairs much in the winter as the downstairs heat rises and does a pretty decent job on its own keeping the upstairs heater from running.

yes the Y1 and Y2 are connected from the outdoor unit, but what confused me is why they bypassed the control board for Y1 and Y2

 

The diagram tinkerman posted indicates my wiring advice is wrong.
Every other make uses Y1/Y2 for 2-stage cooling, it's dumb how they do this.
Trane/american standard are special i guess.

Based on that diagram I would move the wire connected to Y to Ylo.

This alone doesn't mean there aren't other issues, like airflow being set for 2 ton a/c.

Just an important note is that if this system has air ducts in a hot attic, the 2-stage feature will increase capacity duct loss to the attic when running on low due to the air flowing slower through the ducts.
Personally I don't thing 2-stage a/c should be used on a system with air ducts in a hot attic,.

 

Also the Blower is variable speed and currently connected to the BK

 

See note 7, might be your problem.

 

I wonder why is shows Y2 to bk instead of Y2 (labelled y) - what's the point of having a ylo and y/y2 then?

 

Yeah not sure, need to dig further into this. I’m guessing based on your comments around my oversized furnace and that we don’t use a lot of heat in my area, the installer just dumbed down the output by just using a single stage? If so, I can probably move on from worrying about that and concentrate on the blower/ac side?

 

Without the jumper it's locked on low fire.
Effectively like a smaller single stage furnace.
It's possible smaller variable speed blower furnaces aren't stocked in your area so that's why the contractor did that, wanting the variable speed blower to match up with the 2-stage a/c.
There can be a good reason to do something so I'm not going to jump to the contractor messing up in that respect.

Franky if the furnace is very oversized you're better off without the jumper.

To be honest in these hot climates with minimal heating needs I don't know why on earth air conditioners and furnaces are being installed - rather than just going straight heatpump. Being sized for 100+ degree heat and with mild winters, the heatpumps should have enough capacity to not need any strip backup heat.
Even if gas heat is cheaper, the monthly meter charge would offset any savings.

Don't need furnaces in the south it's like using a blowtorch when you just need an electric hairdryer set to low temperature.

 

Thx! I think I’ll move on from worrying about the furnace… although does it matter that the t stat is set to 2 stage for the furnace? I’m guessing it doesn’t as all it’s doing is sending a signal to the control board, and with no wire, nothing will ever happen with the 2nd stage furnace.

any idea why an installer would bypass a control board for the 2 stage AC and just hardwire it directly? Maybe I’m just way off here and none of this has anything to do with the uncontrolled humidity levels, but I was getting ready to replace the x724 so I could hopefully get a little more control to adjust for humidity and discovered these odd things… odd from my novice perspective

 

It doesn't look like it was bypassed as there is a wire on the bk terminal.
It looks like the wire on y should be on y/low.

You would need to trace the wiring carefully as it may have been joined to another wire outside the air handler.

 

So Y1 / Y2 blue/yellow are tied directly together outside of the control board.

I guess I don’t follow what the BK provides here then. I would think BK, Y1, and Y2/low would all be connected to control board 🤷🏻‍♂️

 

Bk would signal blower to go to full speed when it calls for second stage in accordance with diagram tinkerman posted and can also be used for dehumidification features.
There's a black wire on bk.
The Y2 wire from thermostat and to outdoor unit should be connected to wire going to bk -> trace that wire and see where it connects.

I see a black wire on bk of thermostat.

What's the model number of the thermostat?

 

Please forgive my ignorance, I work in tech but hvac is new to me

 

I've reviewed the install manual a little bit for the thermostat, and this is what it shows for 2-stage cooling on a variable speed trane furnace.

It shows nothing connected to Y1 or Y2 at furnace, Y1 and Y2 go right to outdoor unit.

Bk needs to be connected to Bk - I think what it does is directly control the airflow via a pulse width modulating signal ,and that thermostat should have dehumidification controls build in rather than stage signal.
You will need to make sure there any jumper to Bk is removed.

The furnace wiring diagram does show a wire on Y/low, but this could be for when using a non-trane thermostat.

If there is to be a Y wire on furnace control board it definitely needs to be on Y/Low, not Y.
This must be a big part of the problem as with Y energized it will go full airflow no matter what stage.
Another part of the problem could be airflow settings.

I would try to wire it in accordance with the thermostat diagram and see what it does, if the airflow of furnace fan gets staged correctly without a Y connected - and also make sure furnace airflow settings are set for 2 ton a/c.

Thermostat manual setup instructions have to be followed - there's a settings menu, etc.
file: https://sierracoolslv.com/wp-content/uploads/Trane-XR724-User-Guide.pdf

 

I've reviewed the install manual a little bit for the thermostat, and this is what it shows for 2-stage cooling on a variable speed trane furnace.

It shows nothing connected to Y1 or Y2 at thermostat, Y1 and Y2 go right to outdoor unit.
View attachment 846621
Bk needs to be connected to Bk - I think what it does is directly control the airflow via a pulse width modulating signal ,and that thermostat should have dehumidification controls build in rather than stage signal.
You will need to make sure there any jumper to Bk is removed.

The furnace wiring diagram does show a wire on Y/low, but this could be for when using a non-trane thermostat.

If there is to be a Y wire on furnace control board it definitely needs to be on Y/Low, not Y.
This must be a big part of the problem as with Y energized it will go full airflow no matter what stage.
Another part of the problem could be airflow settings.

I would try to wire it in accordance with the thermostat diagram and see what it does, if the airflow of furnace fan gets staged correctly without a Y connected - and also make sure furnace airflow settings are set for 2 ton a/c.

Thermostat manual setup instructions have to be followed - there's a settings menu, etc.
file: https://sierracoolslv.com/wp-content/uploads/Trane-XR724-User-Guide.pdf

Thank you so much, so sounds like Y1 Y2 direct to outside unit is correct. Bk to Bk is correct here.

W1 is connected from tstat to control board (pics and the way the letter were printed on the board make it look like Y is being used but that’s actually W1.

 

I did also have a capacitor recently replaced
On this unit, the tech said they checked the compressor and refrigerant and it checked out ok. Probably a coincidence more than anything I guess.

ill concentrate on the air flow aspect. Probably won’t hurt to clean the inside coils and outside fins… hasn’t been done since install

 

so I set the cooling RH target at 45%

comfort settings

control response set to aggressive
Dehumidify set to Yes
Overcooling limit - 3 degrees
Smart Cont Fan - set to No

https://www.comfortsite.com/Resources/Partners/57e234f5-5dc9-49c2-923f-32d802caa295/documents/724%20IntroductionTK.pdf

 

Just made those adjustments last night fyi

 

Actually looks like I need to go with the 824 to start using the Comfort R on the blower… the 850 and above require some sort of additional relay to be added

 

That thermostat 100% supports dehumidify no need to change thermostat.
No need for slow rampup comfort-r when the thermostat can directly slow the blower on demand- comfort-r to my knowledge is a slow rampup.

When it is hot outside you shouldn't need the dehumidify feature.
The /ac should be running enough at normal fan speed to do that.

Your high humidity problems could very well be caused by furnace blower being set to 1200 cfm on high cooling when it should be set to 800 to 900 cfm.
If the airflow is set incorrectly, any dehumidify mode won't work well anyway.

Do need to go through all the thermostat setup settings though.

 

really do appreciate your help!

 

Looks like according to Manual, cooling air flow is 400 cfm/ton (s3-3 s3-4 off off)

Cooling off delay options s4-1 s4-2 off off

Heating air flow settings - s4-3 s4-4 on off 900/1250 cfm 1st/2nd stage

 

S3-1 and S3-2 appear to be set to off/off which is factory default and for a 3.5 ton a/c.

Since doesn't officially have a 2 ton setting, back it off to 2.5 ton by setting S3-1 to off and S3-2 to ON -> this will push it to just under 1000 cfm on high and probably 60 to 70% of that on low.
After this go through thermostat settings, I would have to thoroughly read the t-stat manual to try and guide you. Maybe tommorow.

If with dehumidify on demand working which hopefully should both slow the fan down and over-cool below setpoint a little it still doesn't dehumidify, back it off to 350 cfm per ton which will get high closer to 800 cfm when set to 2.5 ton/minimum.

It's very possible the slow down fan feature to dehumidify only works when there's a call for low cooling, and if the thermostat is spending most of the time on high that feature won't work much. It depends on thermostat's firmware.

Having the fan speed set too high for tonnage shifts most of capacity to actual cooling instead of dehumidification which is why your new system is running less than old despite being same tonnage.

See from technical datasheet:

 

It cooled down a little this evening. Noticed on my app that that the temp got within 1 degree of set temp, and event changed from stage 2 to fan on. Went upstairs and sure enough it was just showing cooling which I believe is stage 1.

 

Be sure your thermostat is set to auto to shut fan between cycles, continuous fan can cause humidity issues.

 

Appreciate it! Yes, I verified it’s set to auto.

I’ve run this AC since 2020 when it replaced an old Lennox single stage and had zero issues with humidity. I started noticing humidity issues a few months ago after replacing the two downstairs AC/Furnaces. My only theory is that because those two old downstairs were running constantly, they were dehumidifying more? Today, my downstairs one side of the house stays around 46% and the other side, which is more open and has a stair well up to the second floor, is around 48-51%.

 

It’s also interesting that while the humidity is higher in the mornings it’s better controlled, and the AC doesn’t even run that much. Once temps get up in afternoon, and the AC starts running more, humidity levels go up inside, even though outside is lower than the morning

 

It’s also interesting that while the humidity is higher in the mornings it’s better controlled, and the AC doesn’t even run that much.

This isn't totally unusual. When it is cooler outside, the system creates a colder evap coil temperature inside and that removes more humidity quicker. As it gets warmer outside, the evap coil temperature inside will also rise.

 

Monitoring closer today. Started at 50% humidity early this morning and outside was 80 degrees. AC set on 72 degrees. Didn’t run a lot this morning, at times a couple short cycles, but as the morning warmed up, cooling cycles got longer and I even saw longer periods of stage 1 kicking in. At noon I bumped the AC to 75 since we were leaving the house (I use to set to 78/80 upstairs due to low use of upstairs). At 1pm Central I noticed we went from 50% humidity upstairs to 54%. The AC has been pretty much running in either stage 1 or 2 since then, and now it’s 2:45, and AC is staying at 74/75 degrees and not going lower. Temp outside is 87 degrees, and humidity is now 59% upstairs.

In the past few days I was able to maintain 75 degrees on that unit with 95/96 degrees outside.

 

1) Have you verified the accuracy of your humidity readings? many t-stats can't measure it correctly. I have a $500 Lennox t-stat that measures humidity incorrectly by over 20%.

2) You need to get CFM/ton in the 300-350 range for keeping humidity below 50% in humid areas.

 

Wondering if I’ve got a tstat issue… walked upstairs, and it’s cold. Yes still feels a little more damp than I would like. Tstat shows 75 degrees, humidity 60%

Thermapen shows it’s registering 68/69 degrees in the room.

I had purchased a Midea cube dehumidifier a couple days ago. It sits 2 feet above carpet floor level, and currently shows humidity 57% (downstairs is current 52%)

The tstat is about another 2 feet higher on the wall, but the Midea is within 3 feet of the tstat

 

Headed to go get a hygrometer.

 

But I’m really scratching my head on the tstat showing like 5-7 degrees warmer in the room vs a thermapen tstat which is very accurate within a .5-1 degree