Thanks for thhe response

Parker, CO 80134

3,800 sqf with 1500 of that being a finished basement.

3 Ton American Standard AC

Wired as two stage currently but it will start stage one for a while and never catch up before 2nd stage comes on.

House has south facing windows on all levels across the back that are energy efficient and three years old.

The unit that was failing and replaced was a 4 ton and worked great until it started leaking in multiple places. I figured lets just replace the whole thing and be safe. $15,000 later and it performs like crap compared to the original single stage setup.

Try this: Turn up (down) the thermostat 4-5 degrees. First stage will come on but second stage should kick in very quickly. If the second stage reaches the setpoint then you're good. If it doesn't then the system would appear to be undersized and wiring it for 2nd stage only won't help.

Thanks sktn77a! I pretty much do that and it does not keep up still. Sometimes i dont get to lowering to the second stage myself until 11 am or so depending on work and all that. But once real heat hits I’m gonna be in a bad way.

The HVAC people have come around a few times and adjusted the blower speed and measured air and said its working great, meanwhile my house was 78 and not cooling until midnight. I guess I’ll try complaining to them some more!

Appreciate the responses all.

Try and take a temp drop reading.

If you have easy access to where the system sits inside (like a basement) take a temp reading at the return (where your air filter is)

Then record that temp.

Take a temp reading from supply off the evaporator coil.

Air Return Temp - supply temp = ?

Should be at least 15 degrees better if it's at least 20 degrees.

Do this with the unit calling in 2nd speed.

Your house is 2300 sq., feet with a 1500 sq. foot basement. I assume the basement is mostly underground and has a cooling load of approximately zero. If this is true then a 3 ton AC is about the right size. If this is a 2-story house and the second floor is not as cool as you would like, then increasing the size to 4 tons is not going to solve that problem.

I am not sure I fully understand the problem. When the AC is set to maintain a temperature how long is the cycle time and how long does the thermostat stay in the low stage? What temperature are you trying to maintain? If you looking to keep the house below 70 degrees then the 3 ton size is not going to be able to do it on a hot day.

I will set to 68 degrees and hope for the best. On days that are hot it will run constantly all day and the main floor where the thermostat is will get up to 79. Meaning my second floor will be hotter. I dont believe that is acceptable and my previous unit would be able to keep the main floor at most 71. I dont know how long it takes for the second stage to come on during a normal days warming.

They did air temp tests and they were supposedly good. Maybe they also put in a smaller furnace/fan with the smaller AC and it isnt moving air enough for my house and consequently will show better air temp numbers I assume.

I guess if your inside temp at home running up to ~80 is fine then i dont have a problem. If i didnt already have a 4 year old AC system (that was leaking and then replaced) that worked great showing that my house and ducts are able to be what I consider properly cooled I might accept that it’s the best i can get.

The basement vents are closed and its usually cooler than preferred down there.

Just wanting to be confortable in my home without having to replace everything again. Im already $15k deep here.

Well, 68 degrees is going to be a tall order for a correctly-sized AC system in most homes. Most folks keep their homes at ~76 degrees during the summer. However, if it can't get below 79+ degrees when kept on, setting it at 68 degrees isn't going to help.

"They did air temp tests and they were supposedly good" - Meaningless!

Unless the delta is 15-20 degrees, it's not good for a new system with the correct fan speed. You need to verify the numbers (delta at 1200CFM for a 3 ton system) from their testing. The fact that the house was originally spec'd for a 4 ton unit makes me wonder.....................

What thermostat model was installed? Can you hear the AC go into the second stage? It sounds like the AC is always in the first stage and this is the reason why your house is 79 degrees. This is an installation error and you need to call the installer to fix it.

It has the nest pro I believe, which shows when it goes into stage 2. Should i listen to the outside unit or the blower fan at the furnace? I can’t say i have heard a difference but I also haven’t tried to.

When the AC uses the high stage the air flow must increase. You should hear the blower fan at the furnace become louder and you should also feel more air flow. If you cannot detect any difference then you are only using the low stage.

The thermostat may be calling for the high stage, but if the wiring from the thermostat to the furnace is missing or not connected properly then it the two stages will not function. Your old system was a single stage which uses one wire (Y) to turn on the AC. The new furnace has two stages and needs two wires (Y1 and Y2) to control the two stages. One possibility is the there was no spare wire for the Y2 connection and your installer did not want to run more wires. The furnace could be set up to start in the low stage, and then move to the high stage based on a timing setting in the furnace control board. It is not ideal, but would at least allow the high stage to operate.

The old nest thermostat did not use as many wires and the company tried to get out of running the new wire with enough connections, but i argued enough to get it done. Ill try and listen to it tomorrow for a difference between 1 & 2. Thanks for the ideas!

I am also debating a whole house fan to help the AC out, but hate spending the money after sinking so much into the HVAC system.

I gave the blower motor a listen while switching between the two stages, giving it a few minutes to cycle back and forth. I could not hear a change in fan speed while in the same room as the furnace set up. I did not have the opportunity to listen to the outside unit, if i need to do that as well.

"It has the nest pro I believe, which shows when it goes into stage 2."

"I gave the blower motor a listen while switching between the two stages, giving it a few minutes to cycle back and forth. I could not hear a change in fan speed..."

• I have a two stage heat pump with a Honeywell T10 Pro (two-stage-capable) thermostat.
• There is one wire from the thermostat to the heat pump for stage one and a second wire for stage two.
• Wires from the heat pump control board to the blower motor control the blower speed in stage one and stage two. The blower is configured to run faster when the heat pump is in stage two than stage one. You can definitely hear (and feel) the difference.
• Your thermostat might indicate stage two but this does NOT mean that the air conditioner is actually running in stage two. The thermostat has no way to know what the air conditioner is actually doing.
• @mike_home wrote "The furnace could be set up to start in the low stage, and then move to the high stage based on a timing setting". My heat pump would never do this; unless stage two is turned on by the thermostat, it will remain in stage one.
• As other have suggested, the problem is most likely that the wiring is incorrect (i.e., there's no stage-two wire from the thermostat to the air conditioner).
• Could you run stage-two all the time? If I connected the stage-one wire from the thermostat to both the stage-one and stage-two wires in the heat pump, it would always run in stage-two.

The fact that you don't hear or feel a difference in air speed is good evidence your AC is always operating in the low stage. I suspect in heating mode your furnace also only operates in the low stage. You won't know this until a cold night in the winter.

Have you spoken to the installer about the problems you are having? You have spent $15,000 and you are no where near acceptable cooling performance.

There's typically no visual or audible difference on the compressor/condensor operation between 1st and 2nd stage. I've seen reference of some 2-stage designs that reverse the compressor motor direction to change the internal pumping mechanism between low and high stages and thus will turn off briefly and restart when changing stages but you'd need to be outside at the unit at the right moment to catch it. The indoor circulation blower, however, should change between a lower and higher speed.

Stage-switching is best controlled per room temperature differential via the thermostat. The system can't keep up with the cooling (or heating) load on low stage, the room temp lags further from the setpoint so the thermostat triggers the 2nd stage to catch up.

As mentioned above, two-stage switching can be controlled per operational time via a control board on the air handler if the thermostat isn't capable but that is not the ideal. The timer will switch the system to high stage after x minutes of run time regardless of whether it is or is not adequately handling the load. Two of the points of a 2-stage system are 1) to run for longer periods at low stage for better humidity control (cooling), and 2) to hold the room temperature more steady around the setpoint (cooling and heating) vs. larger and perhaps uncomfortable swings that may occur from frequent on/off cycling. Timer control of staging kills those points.

Thanks for the info! i have called the AC people to come check it out, waiting to hear back on when.

In heat mode I can hear the fan sound (I think its the fan) change when going two stage, but not when the AC is in use. The outside AC unit makes a little more of a whine when it goes into stage two.