Opinions for HVAC cooling problem

Discussion in 'HVAC Heating & Cooling' started by Calvin45, Sep 6, 2021.

  1. Calvin45

    Calvin45 New Member

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    Sep 6, 2021
    Location:
    Virginia
    Here is the issue I had a compressor go bad so I replaced the outdoor unit and TXV, I replaced a Trane 14i unit with a American Standard gold 17 Seer 2 stage compressor all and a trane XL90 Gas furnace. Here is the issue unit cools sometimes runs a long period back and forth between stage 1 and 2 which may be normal. The humidity is still rather high about 55-60%, here is what i need thoughts on the large suction line at the outdoor unit is not cold and sweating like it should the coil temp is running at about 37 degrees. My Buddy came over and put gauges on it and put in a little more 410A guages were saying 400 psi on head pressure and other said around 37 degrees, hopefully that sounds ok I'm not familiar with HVAC. He seems to think maybe the TXV may be bad doe anyone have any thoughts are we looking the correct way.
     
  2. fitter30

    fitter30 Well-Known Member

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    Feb 2, 2020
    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Things i want to know subcooling temp ( liquid line temp vrs liquid pressure/ temp) . Exv was changed did tonage match old system and for 410a? Superheat of the exv ? Did the orifice in distributor get replace with the correct size? If not i would run the condenser with blower off to see how the feeder tubes are feeding? What is the temp difference between supply and return ( 18" from coil) with a pocket thermometer. Exv bulb needs to be tight against the piping and insulated.
    subcooling 8-12*
    superheat 10- 14*
    temp difference coil 18-22*
     
    Last edited: Sep 14, 2021 at 3:08 PM
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  4. breplum

    breplum Member

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    You obviously need a NATE certified technician for this.
     
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  5. WorthFlorida

    WorthFlorida The wife is still training me.

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    Was the air handler/furnanced changed with a matching coil? Any AC system rating requires the proper coil. A miss match doesn't mean you have SEER 17. Was the thermostat changed or reprogrammed for 2 stage cool? What model thermostat? Is there a humidity setting? If the humidity is too high the 1 stage cool will run and the fan speed will slow down, therefore, long run times to dry the air.

    https://www.ac-heatingconnect.com/facility-managers/guide-to-txv/
    Understanding the Function of the TXV

    The thermostatic expansion valve controls one thing only: the rate of flow of liquid refrigerant into the evaporator. Contrary to what you may have heard, the TXV is not designed to control:
    • Air Temperature
    • Head Pressure
    • Capacity
    • Suction Pressure
    • Humidity
    Trying to use the TXV to control any of these system variables will lead to poor system performance – and possible compressor failure.
     
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  6. fitter30

    fitter30 Well-Known Member

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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
     
  7. fitter30

    fitter30 Well-Known Member

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    There is only one expansion device better than a txv which is electronic valve taking inputs from liquid, suction and looks at super heat, subcooling. Don't think any manufacturer is using any other expansion devices in high efficiency systems. With the expansion bulb strapped on the suction line and suction pressure its controlling superheat which protects the compressor from liquid floodback, subcooling assures exv getting a full column of liquid and the orifice in the distributor helps with equal flow through the feeder tubes to coil. Todays systems are critical charge with high efficiency condensers and evaporators.
     
    Last edited: Sep 15, 2021 at 2:59 PM
  8. Calvin45

    Calvin45 New Member

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    Sep 6, 2021
    Location:
    Virginia

    The outdoor unit was changed to 3 Ton American Standard Gold 17 2 stage, the coil was replaced with 4PXCCU36B3HAA and left the existing Trane XL 90 2 stage furnace Model TUX080R942W3. Thermostat was changed to 2 stage, the outdoor unit changes stages and the indoor furnace fan also changes. The tstat is a Trane TCONT402. We did replace the TXV and suction line and pressures are better now the suction line is cold and sweating but humidity still seems high may drop to 55%. The fan on the furnace board is set on high cooling, so last night i changed it to the yellow but I couldn't tell any difference. Anything else you'll can think of changing tstat to something newer.
     
  9. fitter30

    fitter30 Well-Known Member

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    Retired service tech
    Location:
    Peace valley missouri
    Humidity goes flows hi to low is the house isn't tight humidity comes right thru the walls or gaps. A blower door test is now it's tested. Your electric company might offer a energy audit that includes this test. Still need the temp drop across evap coil. What size was the old unit and what size was and is the suction line?
     
  10. Calvin45

    Calvin45 New Member

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    Virginia
    The old outdoor unit was Trane XL14i 3 Ton. The suction line going inside is 3/4 inch. The temp this morning was 67 going into coil and 46 coming out, with outdoor temp at 68 and tstat set at 70 degrees.
     
  11. WorthFlorida

    WorthFlorida The wife is still training me.

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    Location:
    Orlando, Florida
    To compare to your home, I have a Florida home built in 2007 with a radiant barrier on all exterior walls and the attic roof is also lined with it. Windows are only single pane, amazingly the only code for windows in Florida is impact resistant. I have a 3.5 ton installed in 2015 Seer 16 Carrier Heat pump unit, one stage cool. Thermostat in the summer is usually set to 77, the power company recommends 78 degrees. The high outdoor temp is at 90 or higher everyday for about 3-4 months year, the AC runs often and it keeps the humidity in control. Right now at 10:00 am it is 85% outdoors, 54% indoors. It rarely gets below 50% in the summer. Come the cooler months without the AC running much the indoor humidity does get 60% or higher. My Smart Honeywell Thermostat sends an email high humidity alert from the Honeywell server. To drop the humidity I'll lower the thermostat to 75 or lower and in an hour or so the humidity is in the 50% range.

    As Fitter suggest you can have leakage sucking in humidity, especially when the dry is pushing out 100 cu ft per minute and the replacement air has to come from somewhere. Did you have a humidity meter with your old system? With your stat set at 70 the indoor dew point drops making it harder to wring out moisture. Another cause it an oversized cooling capacity but having a two stage that runs at 70% of capacity in stage 1 (~25,000 BTU's) it cannot be know unless a heat load was calculated.

    To keep humidity under better control, keep the stat the same throughout the day. If you increase the temp while your out of the home such as for work and then lower it when you get home, the humidity will remain high.

    The cooling stages are controlled by the thermostat and in the manual for your model, stage two kicks in when the set and rom temperature is 2 degrees or higher, a common default setting for most thermostats. The statement from American Standard is not clear how the 70% is controlled. It's possible an outdoor temperature sensor is needed.

    https://www.americanstandardair.com...ing/air-conditioners/gold-17-air-conditioner/
    GOLD 17 CENTRAL AIR SYSTEM HIGHLIGHTS
    • Reduce up to 56 percent of your energy usage with this central air system that surpasses government efficiency standards.*
    • This home central air conditioner runs at 70 percent capacity except on the hottest days when it steps up to the second stage thanks to a two-step Duration™ compressor with two-stage cooling.
     
  12. fitter30

    fitter30 Well-Known Member

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    Retired service tech
    Location:
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    Raise the thermostat temp rh will come down. At 70* @ 50% rh, 75* rh drops to 40%
     
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  13. Calvin45

    Calvin45 New Member

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    Above 71 is to hot for me it doesn't run much when i set it up to above 71, would you recommend a new Tstat that may fit and work better for my system.
     
  14. fitter30

    fitter30 Well-Known Member

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    Peace valley missouri
    Your thermostat is a mini computer heres a installers manual. Need to check the programming for the cycle rate like to see it at 3 that should extend run time should help with humidity. A change in programing might take a few days to make a.difference.
     
    Last edited: Sep 17, 2021 at 10:16 AM
  15. Calvin45

    Calvin45 New Member

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    I have went through the setup and they are set to 3, just didn't know if there is a better or newer tstat that might be more suited for my new heatpump since the one now is 16years old. Could there be any other programming or wiring of fan for example, the fan motor is set to high on black wire not sure how that works since the fan has a low stage and high stage. Thanks for trying to help.
     
  16. fitter30

    fitter30 Well-Known Member

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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Whats your zip code so i can look at your weather
     
  17. Calvin45

    Calvin45 New Member

    Joined:
    Sep 6, 2021
    Location:
    Virginia
    My zip is 24151
     
  18. WorthFlorida

    WorthFlorida The wife is still training me.

    Joined:
    Oct 28, 2009
    Occupation:
    Retired
    Location:
    Orlando, Florida
    Calvin, did you have high humidity with your old system? It may feel warm above 71 because the humidity is high. Dry air always feels cooler and more comfortable. But if it is 68 outside the AC will not run very long because the heat load is low.

    Digital thermostats do not go out of calibration. They work or don't work. If you want to change it, switch to a WiFi model. Remotely you can change the temp and check on the humidity level from anywhere. Honeywell models uses a local weather station for outdoor temp and humidity. I looked over your Trane thermostat model and I didn't notice any humidity settings.

    I check American Standard Smart thermostats and they are the same as Trane.
    ComfortLink™ II XL1050 is the top of the line Trane and the specs do mention humidity control.
     
  19. Calvin45

    Calvin45 New Member

    Joined:
    Sep 6, 2021
    Location:
    Virginia
    I never really checked humidity on old system except for winter because the gas furnace always made low humidity, so its maybe always been hi we always set tstat at 71 during day and 68 at night on the old system always. There are no humidity settings on my tstat so are there tstats that will force the ac to run o help when humidty reaches certain level for control would that be beneficial. So yesterday I set tstat at 71 during the day but humidity was still 60-61 % don't think it ran very much at all
     
  20. fitter30

    fitter30 Well-Known Member

    Joined:
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    Occupation:
    Retired service tech
    Location:
    Peace valley missouri
    Mild weather run time is minimal. Thermostat setup #37 dehumidifier no wiring needed just needs to be enabled two minutes of extra run time. Exhaust fans in kitchen and bathes are they used and run 30 minutes aftershower. Basement humidity high?
     
  21. Calvin45

    Calvin45 New Member

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    Sep 6, 2021
    Location:
    Virginia
    So I feel a little better I ordered a psychrometer Which arrived today the RH is reading 52% on it at 70 degrees which the older meter was reading 8-10 % higher. Does this look better I will enable the tstat setting and see.
     
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