HVAC woes

[escape]

In Nov. of 2021 i bought a new 2.5 Ton Trane Split Heat Pump and Air Handler with a 15.5 SEER. It's a small house: less than 900 sq. feet street level conditioned space and the part of the basement that's renovated less that's than 300 square feet that's also conditioned. There's also an insulated attic of less than 900 sq. feet that's not conditioned.

Since we moved in over 3 years ago, in the summer we've kept the thermostat at 80 in the day and then lowering it to 73 in the evening to go to sleep. I was surprised that this new unit could not keep the house cool when the temps rose above 90. In June I called the dealer to complain and a technician came out and told me there's nothing wrong with the unit, told me to keep the thermostat set at the same temp at all times and charged me for the service call.

Since then I've kept the temp at 78 and still the unit does not keep up - on hot days the temp creeps up to 80 or 81. Again I called the dealer. They told me to set the temp at 74 for a day and see if it could keep up. By 6PM the temp had crept up to 78. Now they're telling me that they'll send a tech out on the next hot day to see if there is something wrong.

The old unit, which was the same size and was 11 years old when I replaced it was able to keep up until it started leaking. It had a lower SEER rating.

I understand that this new unit should have no problem keeping this house cool. The unit is still under warranty and I want to make sure to address any problems before it expires the first of Nov. My questions are: 1. is this unit in fact sufficient for this house and 2. what is my recourse if the dealer does not admit there's a problem? Any help would be much appreciated!

Thank you!

 

[Aerides]

A 2.5 ton unit for 1200 SF? Yes, your capacity is correct. A 3 ton would be for 1500-2000. But I'm confused on the attic part? Is that essentially a 2nd story that's insulated but not part of the ducted-in area? If so, the insulation between your first/basement and this attic is a question. I'm wondering if that part of the house isn't getting part of your cooling capacity unintentionally? Perhaps describe the house a bit more.

It could be a matter of settings, if the air handler is blowing too fast for the air to cool over the coils, etc. Is your duct work, insulation, newer or 50 years old? Either way, your unit should have a 10 year warranty, it's the labor that's only a year.

Before last November, what was the setup?

 

[Bamaman]

You have the right size unit for the Mid South and 1200 square feet.

If you were in Phoenix, it'd be too small--for example.

You could always pay another HVAC guy to inspect the inspection.

I replaced my 3 1/2 ton Trane heat pump a year ago with a 3 ton unit, and it's cooling fine. They had to do some sheet metal repair on the base under the air handler.

 

[escape]

A 2.5 ton unit for 1200 SF? Yes, your capacity is correct. A 3 ton would be for 1500-2000. But I'm confused on the attic part? Is that essentially a 2nd story that's insulated but not part of the ducted-in area? If so, the insulation between your first/basement and this attic is a question. I'm wondering if that part of the house isn't getting part of your cooling capacity unintentionally? Perhaps describe the house a bit more.

It could be a matter of settings, if the air handler is blowing too fast for the air to cool over the coils, etc. Is your duct work, insulation, newer or 50 years old? Either way, your unit should have a 10 year warranty, it's the labor that's only a year.

Before last November, what was the setup?

Thank you for your response..

Yes, I think you can describe the attic is essentially a 2nd story that's insulated but not part of the ducted area. I'm not sure if there is insulation between the main floor and the attic. I don't believe so. There is no insulation between the basement, where the HVAC unit is, and the main floor. The insulation in the attic is in good shape. Duct work was put in about 12 years ago.

As I understand it, the previous unit was comparable but not as efficient. Same duct work.

 

[escape]

You have the right size unit for the Mid South and 1200 square feet.

If you were in Phoenix, it'd be too small--for example.

You could always pay another HVAC guy to inspect the inspection.

I replaced my 3 1/2 ton Trane heat pump a year ago with a 3 ton unit, and it's cooling fine. They had to do some sheet metal repair on the base under the air handler.

Thank you. House is located in central Kentucky.

 

[NW-Bound]

One simple way of checking the operation of an AC is to measure the difference in air temperature at the inlet and outlet. The evaporator should cool the air passing through it by 16 to 22 degree F.

If the AC is too small for the house, it still has to cool the air passing through it. That cool air may just dissipate in a house with poor insulation, for example, or if the house is huge. But it blows out air at the same temperature as it takes in, or just a few degrees cooler, then it is not working right.

The temperature your AC puts out is relative to the temperature you set on your thermostat. So even though there’s no single ideal temperature, you do want a 16°–22° F difference from the supply air and return air. Professionals call this temperature difference the evaporator Delta T.

 

[JoeWras]

It could be a matter of settings, if the air handler is blowing too fast for the air to cool over the coils, etc. Is your duct work, insulation, newer or 50 years old? Either way, your unit should have a 10 year warranty, it's the labor that's only a year.

I want to reiterate Aerides excellent questions. I see installers use default settings all the time which frequently don't have proper fan speeds or other settings.

Ducts sometimes become disconnected on a rework, and if the unit is in a hidden area (attic), you might be blowing cold air into nowhere, or even worse, getting return air from nowhere.

A tech that comes in to check probably won't check these things. They just check amperage and pressures and call it a day.

 

[NW-Bound]

I just measured the evaporator Delta T of the minisplit in my bedroom.

Pointing an infrared thermometer at 1 ft above the indoor unit, I measured 83F. That's the temperature of the air near the ceiling that the unit draws in.

Pointing the thermometer at the outlet vent, I measured 60F as the temperature of the air it blows out. That's a difference of 23F.

The temperature of the room at chest level is 78F. Outside temperature is currently 104F. The variable-speed minisplit is currently running at a low speed, self-selected as it is designed to do.


PS. I repeated the above exercise with the larger mini-split for my living area. Inlet temperature: 83F. Outlet temperature: 68F. Delta T: 15F. Chest-high temperature: 77F.

 

[bobandsherry]

Measure the temp coming out of your vent. Then measure temp at return. Vent should be a minimum of 15 degrees cooler than the return. If not, then there's a problem with the cooling.

You mentioned you replaced a unit, mentioned it's SEER rating, but what's more important is the ton size. SEER is only how efficiently it cools vs energy used not the cooling capacity. Was old unit same size as new unit?

 

[escape]

Measure the temp coming out of your vent. Then measure temp at return. Vent should be a minimum of 15 degrees cooler than the return. If not, then there's a problem with the cooling.

You mentioned you replaced a unit, mentioned it's SEER rating, but what's more important is the ton size. SEER is only how efficiently it cools vs energy used not the cooling capacity. Was old unit same size as new unit?

Thank you for your response. Old unit was same size.

 

[Aerides]

I also wouldn't be too worried about your AC team 1 year warranty- consider that a sunk cost. Doesn't matter if a useless team keeps coming back for free, vs. a good, qualified team that charges for a couple of visits.

Look in your area for the type of place you'd like to have a maintenance agreement with, usually includes a visit or two per year. We bailed on our install team and went with someone else, after...competence issues. And a lot of AC techs aren't smart on whole-house stuff. And even fewer are smart on today's more far more complex systems.

If your unit is the right size, cooling to 20f less than outdoors is no big deal. And then never getting more than 1 degree over your setting, coming on, cooling back down, repeat. Getting your there might take a better team than you currently have.

But this is where a bit of blow-that-dough is well justified - to be comfortable in your home.

 

[NW-Bound]

Infrared thermometers are so cheap, there's simply no excuse for not having one. More than checking your AC, they can be used to measure temperatures of different things, such as your frying pan, your oven, your BBQ to verify their setting or temperature display.

When checked against a $99 Thermapen (contact thermometer, not infrared) which is guaranteed to 1F accuracy, I have found my infrared thermometer to agree within 1F. Not bad for something which cost me $25 bought a few years ago.

Here's a current one on Amazon:

 

[travelover]

Aside from checking the temperature delta across the air handler, I'd look for disconnected ducts on both the inlet and outlet sides. Check the outlet temperature at every register to identify a potential problem area. Also double check the air filter to see if it is restrictive and look at the fins on the condenser and evaporator for dust / dog hair build up.

 

[latexman]

If the old unit kept the house cool in mid-August, I would bring the hammer of Thor down on that dealer and technician!

If not satisfied with their response, contact Trane!

 

[W2R]

Glad you called the AC company back and plan to tell them what's going on. They'll probably come out, figure out what's going on, and take care of it. That's what they do for a living. You don't need to make any measurements or do anything - - they'll still do that anyway.

What you are describing is just unacceptable. A good, new Trane system should be able to do better than that.

I got a new 3.5 ton Trane HVAC system installed in my 1500 sf home back in 2016, and it is fantastic. Yes, that's a higher tonnage than most houses this size require, but as you know a good AC man puts more than square footage into the computations.

The exact same AC man put a new Trane system in Frank's house, next door, a couple of months after doing mine. Even though his house is a few (30?) square feet bigger than mine, the guy chose 3.0 tons for his house. It works perfectly as well.

In June and early July, we had high temperatures over 100F outside in my suburb almost every day. My Trane kept up with no problems. I did change the filter every few weeks (despite being a cheapskate), so maybe that helped. Frank had his AC never cycling off (even though his house was comfortable), so he had the guy come out and do the annual tune-up/inspection/maintenance. That took care of it. I haven't ever had that done yet although I know people say I should.

 

[NW-Bound]

Glad you called the AC company back and plan to tell them what's going on. They'll probably come out, figure out what's going on, and take care of it. That's what they do for a living. You don't need to make any measurements or do anything - - they'll still do that anyway...

Well, they will come out, do nothing and charge the OP for doing nothing. Ka ching! Rinse and repeat.

The more you know about what to expect out of your system, the harder it is for an unscrupulous or incompetent serviceman to BS you.

... In June I called the dealer to complain and a technician came out and told me there's nothing wrong with the unit, told me to keep the thermostat set at the same temp at all times and charged me for the service call.

 

[NW-Bound]

Another thing to check into is how your current electric bill compares to your past bill with the old unit.

An AC that does not properly cool or has a leak in the air duct will run longer and consumes more energy, while not keeping you cool.

 

[travelover]

..............Yes, that's a higher tonnage than most houses this size require, but as you know a good AC man puts more than square footage into the computations...........

With air conditioning systems, bigger isn't always better. An extra large air conditioner will short cycle and not remove excess humidity. There is a program that inputs square feet, window sizes and exposure, insulation, etc that will accurately size an air conditioner or furnace, but most installers are too lazy to do the measurements and run the program.

 

[W2R]

With air conditioning systems, bigger isn't always better. An extra large air conditioner will short cycle and not remove excess humidity. There is a program that inputs square feet, window sizes and exposure, insulation, etc that will accurately size an air conditioner or furnace, but most installers are too lazy to do the measurements and run the program.

They all run the program here, AFAIK. They can even do it on the tablet computer that they carry with them. Also, people here say that New Orleans is the country's biggest small town... because everybody here knows everybody and reputations matter. Frank's family has been here forever, so he knows everybody and found out who to get for HVAC work. We are very happy with the HVAC systems they installed for us.

 

[JoeWras]

With air conditioning systems, bigger isn't always better. An extra large air conditioner will short cycle and not remove excess humidity. There is a program that inputs square feet, window sizes and exposure, insulation, etc that will accurately size an air conditioner or furnace, but most installers are too lazy to do the measurements and run the program.

Absolutely. And additionally, this is where the fan speed setting is crucial. A fan speed set too high for the tonnage won't remove the proper amount of humidity.

These settings are usually set internally through jumpers, DIP switches or a menu on the internal controller. Good HVAC techs will check this against all the calculations. Bad ones are: "Fan speed setting? What now?"

 

[freedomatlast]

Infrared thermometers are so cheap, there's simply no excuse for not having one. More than checking your AC, they can be used to measure temperatures of different things, such as your frying pan, your oven, your BBQ to verify their setting or temperature display.

When checked against a $99 Thermapen (contact thermometer, not infrared) which is guaranteed to 1F accuracy, I have found my infrared thermometer to agree within 1F. Not bad for something which cost me $25 bought a few years ago.

Here's a current one on Amazon:

Maybe accurate to 1 degree only if corrected for emissivity of the surface being measured. Much better off with a probe with a small wire like this plugged into a multi-meter: https://www.ebay.com/itm/224769705111?hash=item3455518497:g:WxIAAOSwNaNh0HBV

 

[frank]

I would check the vents in every room and see is you have good airflow. if ducts become disconnected then they do not move they air to where you want it. could be such a thing as low freon is icing up your a-coil or condenser. try just running the fan for a few hours and then turn the cooling cycle back on and see if makes a difference.

 

[UtahSkier]

I just went through this with my own home.

Open all vents and remove your air filter. Measure the delta T between the return and all the vents. Report back the maximum delta T and the max delta between the vents.

Do the same with your air filter in.

Another helpful measurement is the supply side at the handler. Stick a temp temp probe into the output air stream. This will show you the temperature of the conditioned air. The hole can be sealed with some aluminum tape.



If delta T is too large, then you are not getting enough air over the coils.

 

[NW-Bound]

Maybe accurate to 1 degree only if corrected for emissivity of the surface being measured. Much better off with a probe with a small wire like this plugged into a multi-meter: https://www.ebay.com/itm/224769705111?hash=item3455518497:g:WxIAAOSwNaNh0HBV

This type of temperature sensor is called a thermocouple. Type K is most commonly used. You will need a DVM which has a jack for a thermocouple; not all DVMs do. I have 2 DVMs with a thermocouple jack myself.

Thermocouples have several advantages, one of which is the small size which lets them stabilize very quickly to the temperature of the object you want to measure, which is the airstream in this case. Another major advantage is robustness, due to its simplicity. For the last reason, thermocouples are widely used in industrial applications.

However, the accuracy is only to a few degrees F. One can check this out against a good thermometer, such as one for measuring body temperatures. A medical body thermometer would have a disastrous error effect if not good to less than 1F, although it is designed for a narrow temperature range.

Yes, you can add a thermocouple to your tool kit too. If you buy a DVM with a thermocouple input, the DVM will come with the sensor as a kit.

An IR thermometer is very useful to remotely check the temperature around the inside of the home for hot spots or cold drafts. It is sensitive enough that I can point it at my bed where I lied down, and it can see the residual heat from my body left on the mattress. Really neat.

And the IR thermometer allows me to check the outlet temperature of my mini-splits any time, which are mounted 11 ft from the floor (due to vaulted ceilings).

If in a tight spot, you can use a cooking thermometer, but it needs to be kept in the airstream of an outlet for 1 minute or so to stabilize. A thermocouple will take perhaps 5-10 seconds. An IR thermometer, instantaneous.

PS. The limiting factors of the accuracy of a thermocouple are the following: 1) the sensitivity of the dissimilar wire junction is very low at about 22 microvolts per deg F, and 2) the accuracy of the cold-junction compensation (circuit inside the DVM).

 

[freedomatlast]

This type of temperature sensor is called a thermocouple. Type K is most commonly used. You will need a DVM which has a jack for a thermocouple; not all DVMs do. I have 2 DVMs with a thermocouple jack myself.

Thermocouples have several advantages, one of which is the small size which lets them stabilize very quickly to the temperature of the object you want to measure, which is the airstream in this case. Another major advantage is robustness, due to its simplicity. For the last reason, thermocouples are widely used in industrial applications.

However, the accuracy is only to a few degrees F. One can check this out against a good thermometer, such as one for measuring body temperatures. A medical body thermometer would have a disastrous error effect if not good to less than 1F, although it is designed for a narrow temperature range.

Yes, you can add a thermocouple to your tool kit too. If you buy a DVM with a thermocouple input, the DVM will come with the sensor as a kit.

An IR thermometer is very useful to remotely check the temperature around the inside of the home for hot spots or cold drafts. It is sensitive enough that I can point it at my bed where I lied down, and it can see the residual heat from my body left on the mattress. Really neat.

And the IR thermometer allows me to check the outlet temperature of my mini-splits any time, which are mounted 11 ft from the floor (due to vaulted ceilings).

If in a tight spot, you can use a cooking thermometer, but it needs to be kept in the airstream of an outlet for 1 minute or so to stabilize. A thermocouple will take perhaps 5-10 seconds. An IR thermometer, instantaneous.

PS. The limiting factors of the accuracy of a thermocouple are the following: 1) the sensitivity of the dissimilar wire junction is very low at about 22 microvolts per deg F, and 2) the accuracy of the cold-junction compensation (circuit inside the DVM).

I agree with what's stated above, but without an emissivity correction on the IR gun, a quality thermocouple will still be more accurate for the purposes discussed in this thread. At the very least, an operator of an IR gun should be aware of it's limitations and how it works. I'll gladly wait 5 to 10 seconds for an accurate reading from a thermocouple over an instantaneous, potentially inaccurate reading from an IR gun that hasn't had emissivity dialed in. Looking at the IR gun shown in the picture, it appears that one doesn't have the means to adjust for emissivity.