Brand New Heat Pump and AC Can't Cool House to less than 75.

mpkozar

We had a new Trane, XR 14, 2.50 Ton HP Condenser Model 4TWR4030 and Trane, Hyperion Series 2.5 Ton Air Handler Model TAM40A30 installed last September. The installer supposedly tightened up all of the duct work in the attic. This is a two story bungalow with 1400 SF on the main floor and no ductwork to the basement except for one return vent to pull out humidity and we live in Maryland. We really didn't use the heat since we have baseboard hot water which we prefer. The last few days the temperatures have been in the 80s-low 90s. The tstat is set for 75 degrees and the thing runs all day until it cools off in the evening. I've taken temps at the supply vents and on the hottest days the temp difference between the return and supply is less than 14 degrees to only 7 degrees from the back bedroom. When the outside air temp is in the low 80s it ranges from 9-16 degrees difference from indoor air.

The previous unit was AC only and the air handler was 110 volts, the new one is 208 and the system is using the existing ductwork but as I said they checked it when they installed the unit.

Shouldn't a new unit perform better than this? I'm going to have the installer come out again since its still under warranty but I just don't understand why I'm not getting better cooling. Any suggestions on what I should ensure he checks?

Thanks in advance,

mk

EBEBRATT-Ed

Check the air temp at the AHU return and supply with a good thermometer after it has been running 20 min or so. You should get a 30 deg differential

SuperTech

The problem could be the refrigerant charge, the first thing I would do is make sure that the system is charged to the manufacturer's subcooling specification. Next thing to do is make sure that the Hyperion air handler is setup for the proper tonnage and make sure the external static pressure in your existing ductwork is acceptable by Tranes specifications.
I'm not a big fan of those plastic air handlers, I've found that setting them up is more of a pain than it should be. Seems like a bad design all the way around. Location of the circuit boards is terrible.

HVACNUT

Get the installer back.

Is 75° the design indoor temperature?

What size was the old system? And no problem maintaining temperature with it?

By "tightened up the ductwork", did they tape or mask all joints? Could it pass the 25 Pascal duct test? Some areas require a permit and test even if it's just a swap out.

How humid is the basement?

Ironman

Your post is too vague to attempt any kind of diagnosis. We'd need readings taken with the proper test equipment to do that. Your temperature readings do indicate that it's not performing properly, but they are sufficient to indicate what the problem is.

Call the installer back and tell him it's not cooling properly. He should not only check the refrigerant charge, but should also check the static duct pressure against the manufacturer's blower performance charts to assure that the air flow is correct.

pecmsg

1 return to pull out moisture? Where is it getting its makeup air, from outside?

What was the size of the old system?

What duct work was done?

EBEBRATT-Ed

I made a mistake on my post above you should get a 20 deg diff across the AHU not 30 deg. Hit the wrong button

ChrisJ

> @EBEBRATT-Ed said:
> I made a mistake on my post above you should get a 20 deg diff across the AHU not 30 deg. Hit the wrong button

That seems very dependant on humidity.
I'd say anything 17-23 degrees could be considered normal.

30 needs a new filter for sure tho

mpkozar

The installer came out and checked the refrigerant charge and it was ok. He checked the air handler in the attic and there was some openings that were pulling in attic air. He sealed the holes and yesterday it ran for over 5 hours and struggled to get the indoor temp to 75. He said he didn't check the rest of the duct work because it was very hot in the attic.

Today the temp is 93 its been running for a few hours and still can't get the temp to 75. In fact, the indoor temp has gone up to 77. I've got an attic fan that isn't working and when I called they said that everything checked out and they blamed it on the attic fan. I have an electrician coming tomorrow, but the attic temp is 120 and I don't think the fan will make that much difference when the outside air is over 90.

I wasn't sure if you could attach files before, but I've attached a spreadsheet I've been keeping of the temps at the return and the supply registers. It looks to me like hot attic air is still getting into the returns. The installer gave me some crap today about the attic fan, but he's coming out again tomorrow morning.

The previous system was installed by Sears in June 2000. It was a Heil HAC230AKA with a MB12F1900A air handler. It never ran constantly and worked great until we replaced it last September - the condensate pipe got plugged, the safety pan failed and the ceiling collapsed from the water.

Thanks for all the suggestions so far.

mk

mattmia2

Either there is something wrong with the refrigeration system, something wrong with the new ductwork that it isn't able to move enough air, or a massive leak in the ductwork or misconfiguration of the air handler. The subcooling and superheat can be correct but the capacity low if it isn't moving enough air. Get them to tell you what the subcooling is, that is the only proper way to check the charge in the system (after correct airflow has been verified). It isn't something stupid like the condenser blocked with cottonwood or something is it?

ChrisJ

So what's the temp drop from your return to the vent closest to the unit? 14 degrees?

What size was the old system?

EBEBRATT-Ed

Try closing up your basement return for a while and see what happens.

A good technician that knows what he is doing will find the issue in an hour or less. But you could have multiple issues like leaking ductwork and a refrigeration problem. At this point everyone is guessing.

Do this. When the tech comes back make him give you the air supply and return temp at the ahu......not at the registers.

Abd get superheat and subcooling readings of the refrigeration system

Then we will know where to look

HVACNUT

Get the owner out there. Explain that the old 2.5 ton Heil had absolutely no problem cooling. Same attic so that's BS. Attic fan or not.
They can make it right or rip it out.

mpkozar

Attached is the outcome of this mornings service call. It's not too hot here yet so still don't know if this will solve the problem. He said there was a 20 degree difference between the supply and return at the air handler, added 12 oz of refrigerant to increase the subcool from 6 to 11, and increased the airflow from 875 cfm to 1000.

It's not very hot here yet, but I'm hoping this works. Yesterday the AC ran from noon to 9:45 PM non-stop and the temp in the house rose from 75 to 77 before it cooled down in the evening - after a thunderstorm.

HVACNUT

How did he wind up with a 72° return air temp when the thermostat is set to 75°?

See what happens. Suggest they return when there's a heavy load on the system if this doesn't work.

ChrisJ

HVACNUT said:

How did he wind up with a 72° return air temp when the thermostat is set to 75°?



See what happens. Suggest they return when there's a heavy load on the system if this doesn't work.

Thermostat is in warmer area?
Some supplies are near returns?

mpkozar

It was cooler today and the AC didn't run continuously. I had the tech come out early in the morning so it was cooler in the attic. He turned the tstat to 64 so the unit would stay on while he was working so its possible the temp was 72 when he tested supply and return temps.

So far the system has turned on and off as it should and its 88 now so maybe this will work.

This is a 2.5 ton system. Shouldn't it have been set at 1000 cfm from the start?

Ironman

You'd get better de-humidification with it set to 875 cfm, but less sensible capacity. 350 cfm per ton is acceptable if it doesn't create any other issues. 400 cfm per ton is the general rule, but every system and house may need something a little different.

mattmia2

12 oz is kind of a lot in a system that size, that likely was the issue. You could experiment with turning the airflow back down and see how that performs. Dehumidification is probably your main goal. I'm not going to dig for the spec for that particular system, but 11 Fahrenheit degrees is a more typical spec than 6 F. If I were charging a TXV system in absence of documentation, I would aim for something around 10 F degrees.

EBEBRATT-Ed

Sounds like it was undercharged and also low on airflow.
1000cfm or 400cfm/ton is where it should be to start. If you need more dehumidification you can lower the air flow .

The most important thing is your getting a 20 deg difference between supply and return air at the ahu if his measurements are correct and the system is not leaking refrigerant you should be ok

icy78

IF the numbers given are ACCURATE, this is what you are getting approximately. See the screenshot.

2.5 ton system
1000cfm
72/62 db/wb return
52/? Db/wb supply
I'm guessing 51 wet bulb supply.
That's a 6.67 btu delta Enthalpy which is typical of a "normally operating system"

That gives you 31117 total btu.
About 21000 sensible heat , verified by
1000 x 20 x 1.08 =21600 btu
It could be that your old AC was an actual 30kbtu plus, and the new one is less. That's fairly typical.
More likely are inaccurate readings by the tech.
In particular the CFM. Be nice to know the supply wetbulb also.
Off the top of my head you have a 0.6 Sensible heat ratio. That's alot of latent load. (Moisture) wheres that coming from?
Also are the temperature numbers inaccurate now that the cfm was changed?

unclejohn

How did they get the 230v into the attic? Did they run a new circuit or take the old neutral and make it a hot line. If they did how are they grounding the A/H. The plastic design makes it tough to ground properly. I thought Trane stopped making that A/H.

ChrisJ

unclejohn said:

How did they get the 230v into the attic? Did they run a new circuit or take the old neutral and make it a hot line. If they did how are they grounding the A/H. The plastic design makes it tough to ground properly. I thought Trane stopped making that A/H.

You would only ground where they provide a ground lug for electronics or metal inside the cabinet. 12-2 or 14-2 romex or MC would be perfectly normal for a single phase 230/240 circuit and has an uninsulated ground conductor.

What do you feel could be happening?

mpkozar

I had an electrician install a 60 amp circuit.

So far it's been cool in MD, but its supposed to get warm again in the next few days so we'll see if the modifications worked.

ChrisJ

mpkozar said:

I had an electrician install a 60 amp circuit.

So far it's been cool in MD, but its supposed to get warm again in the next few days so we'll see if the modifications worked.

Why!?!?

JUGHNE

60 amp probably for heat strips for the HP air handler, sounds like 10 KW.
You would want them during defrost of the outside unit.
Though he has a boiler also so may not use the HP that much.

ChrisJ

JUGHNE said:

60 amp probably for heat strips for the HP air handler, sounds like 10 KW.
You would want them during defrost of the outside unit.
Though he has a boiler also so may not use the HP that much.

I suppose that's fine and all, but it certainly has nothing to do with the units ability to cool or dehumidify. Unless he's got it configured to use those electric strips as reheat but that's really unlikely.

JUGHNE

It is rare, but it has happened that one or part of one strip is energized.
I have found this several times in older units. One coil broken and grounded to unit. Often only one leg of the heater is controlled by a relay.
The other leg is always on, perhaps cycled by high limit as in fan failure.
A patient amp probe check on both legs when AC/fan is running could confirm this.
This could be done at the main panel, not requiring an attic visit.