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I recently had new HVAC installed. I am noticing it being little louder than what I had previously. The new system is American Standard 80% efficiency with ECM blower motor. My question is

  1. Can I reduce the fan speed to make it little quieter? - I asked the contractor who installed it and he said he can certainly changed the fan speed but there might be and issue that your ac may get icing. So is that true that by reducing fan speed may create icing issue?

  2. AC is not Turing off automatically even when temp reached to set point. I have checks that the fan is on auto setting and thermostat shows the set temp. If I increase the set temp to higher than what is currently on display then it shuts off automatically but when it gets to desired temp, it does not shut off automatically.

What could be the issue? Thermostat or faulty wiring?

Thank you in advance.

  • You say it does not shut off when it reaches the set point. In that case does the temperature go below the set point and keep going lower and lower? Or does it finally shut off 2 deg F or so below the set point? Do you have an advanced system that controls both temp and humidity? If so perhaps the condensing unit goes to a lower refrigerant pumping rate and settles into a steady state maintenance mode to keep the temp at the set point without cycling off and on. – Jim Stewart Aug 1 at 19:20
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    Let the unit operate without intervention and see how it performs. – Jim Stewart Aug 1 at 19:28
  • Yep this is exactly what “dead band” is doing to save $. – Ed Beal Aug 1 at 19:35
  • @Jim, It stays at set point and temp does not go below the set temp. But what I have noticed more is that it keeps running about 2 hrs and then shuts off for hour or so then turns back on and again runs about 2 hrs. But the set temp and actual temp remains the same through out the cycle. My understanding is that as soon as the actual temp reached the set temp it should immediately turn off. – Mayur Aug 2 at 2:35
  • So the air handler inside is staying on, but could you check to see if the condensing unit outside is cycling off and on? There are dual compressor condensing units in which (I think) only one compressor runs when the cooling demand is relatively low. These are very quiet and efficient and you will have to look closely to see whether the condensing unit is even on. What is the make and model of your unit? Where is this? I am personally unfamiliar with high efficiency units but a long running air handler is not necessarily a fault condition, it may be a feature. – Jim Stewart Aug 2 at 16:34
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If the evaporator will ice up depends on the type of control if it is orifice or capillary tube control it may Ice up but if a thermal expansion valve called TXV this regulates the flow and it should not but I have seen TXV controlled system ice up a few times. As far as your system not shutting off when the temp is reached this is to keep the system from short cycling there is a setting sometimes called “dead band” usually around 3 degrees and is set in your thermostat it may be a setting like +2 -2 this would be a 4 degree dead band or the thermostat won’t turn the heat on until 2 degrees below set point and won’t shut off until 2 over set point same with the ac, you can usually change these I change mine based on season +0 -2 is my summer setting and +2 -0 is my winter setting. If it takes 10 minutes to change 1 degree a 2 degree dead band is ok but if you reduce it two far your energy cost will go up and the life of your system may be reduced from the repeated startups.

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  • You know,changing the dead zone like that is no different than changing the sticker on your amp’s volume knob so it goes to 11 lol. – Harper - Reinstate Monica Aug 1 at 19:13
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    Not exactly it tells the thermostat when to turn on and off. I have set it to 0 +- yes it turns on and off with the settings but is hard on an hvac system , like a heat pump never shut down going from heating to cooling in 1 minute. Yep tried it , saw my electric bill jump 100+ a month but the temp was right there. , bump it by 2 to 4 and save 100 or more on peak months both summer and winter. – Ed Beal Aug 1 at 19:33
  • @ed so you suggest having and dead band of around +_ 2 is good in terms of saving some $$$ as well as performance of the unit? – Mayur Aug 3 at 0:02
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    Yes this allows the unit to run with fewer startups, ac compressors draw a substantial amount on startup so by having a dead band it runs a little longer Getting slightly cooler than the set point and turns on just above for a 4 degree swing on my 5 ton unit that was 100$ per month difference I don’t remember what it was +0 -2 or 2 degree swing it was not a straight comparison I think it was 65 or 70$ less than 0 dead band my wife noticed the 4 degree swing but was fine with 2. I started this when I adjusted my trunk dampers to push more air upstairs in summer and down in winter. – Ed Beal Aug 3 at 13:51
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What I get from searching on your model is that your condensing unit is a basic single compressor model with a modest SEER of 14 or 16 depending on which evaporator and air handler it's paired with so I doubt you have a variable speed compressor, although you might have a two speed condensing fan.

However, your air handler inside is described as having a variable speed motor. This could mean it is continuously variable in a range during cooling or just has two speeds in which a higher speed is used for a/c and a lower speed is used for heating. Can you tell if the fan is varying in speed? Is it louder sometimes and quieter others?

The long run time of your air handler after setpoint is reached is unusual in my experience but could be a feature of this type of air handler. For the time being I suggest you just use it without over controlling, but keep records on how long the air handler is running.

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  • I have to check on variable speed. But like I mentioned earlier that it runs for hour and then shut off for hours and then again runs for hour. So not sure if anything is wrong or I am just over thinking. – Mayur Aug 4 at 23:00
  • Sorry I take my words back about it running for constant 1 hr. Because last night it ran for 45 min and then turned off. Since this is only 5-6 day old in my house I am still discovering lot of things about it. I guess I did not pay this much attention to my older unit. – Mayur Aug 5 at 15:42
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Thanks folks for taking time answering my question.

I upgraded to new thermostat and now my AC cycles fine. (10-15 min on avg hot day).

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  • Thanks for coming back. Would you add a bit more info to your answer (e.g. new thermostat make/model)? Then you could accept your answer as the best for your question. – Daniel Griscom Sep 7 at 16:46

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