Performance problem suggested by delta-t?

[ls3c6]

I have a 2001 built bi level with 1000sq/ft per level, basement is about half submerged underground. R60 in the attic, R20 or equivalent in the walls, new energy star doors and double pane windows with blackout drapes in front of all of them.

During the summer I keep the supply vents closed downstairs as it stays very comfortable down there on it's own, there are dedicated return vents upper and lower so no moisture buildup downstairs.

With an outdoor temperature of 86 and the AC having been set to 74 most of the day the interior temperature is 74 and RH is 38-40%. The AC does a very good job of removing humidity, however when I checked the return temperature at the air filter I got 70.1f and at the nearest supply vent I got 57f... only a 13f split.

Does this indicate a problem, do I need to call someone to take a look at the refrigerant charge? I always run the cheap green filters and change every 30 days, AC is run on the black/high fan wire. Outdoor coil is clean.

[54regcab]

If RH is 40% you have enough Delta-T. Low delta-T typically has high humidity as as symptom.

[Rhino32713]

You have not said if you have had a professional A/C company out to do maintenance on this unit. Most manufactures recommend this once a year. I would invest in a service by a license contractor.

[kb3ca]

How far away from the coil was the "nearest supply vent"? You need the check the air temperature about a foot after the evaporator coil to get your best reading. With humidity levels that low everything is probably ok.

[tbirdtbird]

It doesn't sound like you have a problem.

[ls3c6]

If I meter from the supply manifold itself there is an access panel just in front of the coil, from there i'll see 20-25f delta-t.

So you're saying since the system quickly lowers indoor humidity, once indoor humidity is very low/comfortable a 13f delta-t is acceptable?

[JamesCPH]

If you have a 20-25F delta T at the unit your system in performing well. You cant measure Delta T from the farthest supply and get an accurate measurement of how the actual unit is performing.

Is your ductwork in the attic or the basement?

[udarrell]

If I meter from the supply manifold itself there is an access panel just in front of the coil, from there I'll see 20-25f delta-t.

So you're saying since the system quickly lowers indoor humidity, once indoor humidity is very low/comfortable a 13f delta-t is acceptable?
It works the opposite way.
The lower the humidity is especially below 50% the higher the delta T should be, a 13-split would not be nearly enough split, the split should be above 20F at 40% RH.

The level of humidity has a greater effect on the split than does blower CFM, but that should usually be, except in hot & dry climates, between 350 & 400-cfm per/ton of cooling.

A very high indoor humidity could drop the split as low as 12 to 14-F.

Seems like it could be picking up too much heat in the ducts...(?)

[ls3c6]

Ducting runs inbetween the levels in the center, air handler is on the lower level in the center. All areas are finished upper/lower... Should I be leaving the lower supply vents closed as I have been? Its always cool down there.

Seems I need to get someone out here if the split's that poor with 38-40% indoor RH?

[catmanacman]

with that delta t I would say time for a service call

[mason]

Your on an hvac thread because your worried about your system, I would say that you should have a company come out and service your unit to put your mind at ease. Make sure they are a reputable company and let your tech know all of your concerns, but don't tell him that you've been looking at the wiring and performing any diagnostics on your unit unless you want to get charged more.

[ChrisTechMech]

If I meter from the supply manifold itself there is an access panel just in front of the coil, from there i'll see 20-25f delta-t.

So you're saying since the system quickly lowers indoor humidity, once indoor humidity is very low/comfortable a 13f delta-t is acceptable?

If your TD is 20-25 about 1' from the evap coil, you're fine. Esp if your RH is 40-50% and your house is maintaining setpoint. If you don't have a place to take a temp reading, drill a small hole just off your plenum (middle of the take off) and stick your probe in there. Put a screw or tape in place of the hole. CAUTION!!! PAY ATTENTION AND DON'T PUT A HOLE IN YOUR EVAP COIL PLEASE! THIS WOULD BE A BAD THING! I don't think you have a problem though. Don't be so intent on finding a problem that you create a problem.

[ls3c6]

Well just wasted $ for a contractor to waste 3hrs lessening and increasing the R22 level because the superheat wouldn't come up the specified 7-10f, suction pressure and superheat temp stayed the same and would not deviate.

It's a heil/arcoaire 2.5 ton with an "aftermarket 2.5 ton ADP" indoor coil, which he now blames the "piston" is for the problem and spending another $ will fix it :/

[ChrisTechMech]

Well just wasted $ for a contractor to waste 3hrs lessening and increasing the R22 level because the superheat wouldn't come up the specified 7-10f, suction pressure and superheat temp stayed the same and would not deviate.

It's a heil/arcoaire 2.5 ton with an "aftermarket 2.5 ton ADP" indoor coil, which he now blames the "piston" is for the problem and spending another $ will fix it :/

Did he say your delta-T was low? What was the SH before he started? Do you know if he let the A/C run at least 15 minutes before adjusting the charge? I'm curious, why did you choose to check your A/C in the first place? Was it not keeping up?

[mason]

Don't list prices. All he did was mess with the charge? No coil cleaning or anything? Three hours on one call is a lot of time to not be changing a compressor or a coil, was he a newbie or something.

[lynn comstock]

If I meter from the supply manifold itself there is an access panel just in front of the coil, from there i'll see 20-25f delta-t.
.... I think you might mean that the delta T measured close to the coil is 20 to 25°F. If so you are fine.

The delta T at the first register is low for some other reason. I suspect that measurements elsewhere will be better as the system performance seems reasonable.

[ls3c6]

Everything was clean, head pressure was 215psi... he was certified and claimed to be doing this for "16yrs" but kept saying "I can add or subtract refrigerant all I want and hte low pressure never increases above 67psi / 40f, something is wrong"

He bled the compressor down to check for a vacuum leak, none existed.

My problem with the system is it's a 2.5 ton and i'm only cooling the upper level... 1000sq/ft and while it keeps the humidity tolerable it's nearly impossible getting it to 72f which seems unreasonable in a house this tight with no sunlight entering and R60 in the attic.

At the end of the day he cycled enough R22 until we ended up with a +10f superheat, but that will cycle between 0 and +10 as it continues to run... he blames the coil, wrong sized piston SOMETHING in the a-coil... but im' not convinced

Either way i'm back to where I started a little more poor

[udarrell]

Everything was clean, head pressure was 215psi... he was certified and claimed to be doing this for "16yrs" but kept saying "I can add or subtract refrigerant all I want and the low pressure never increases above 67psi / 40f, something is wrong"

He bled the compressor down to check for a vacuum leak, none existed.

My problem with the system is it's a 2.5 ton and I'm only cooling the upper level... 1000sq/ft and while it keeps the humidity tolerable it's nearly impossible getting it to 72f which seems unreasonable in a house this tight with no sunlight entering and R60 in the attic.

At the end of the day he cycled enough R22 until we ended up with a +10f superheat, but that will cycle between 0 and +10 as it continues to run... he blames the coil, wrong sized piston SOMETHING in the a-coil... but I'm not convinced.
Either way I'm back to where I started a little more poor

Well, U shouldn't need to get it to 72F to be comfortable.
What's wrong with 74F & 50% RH with air circulation?
Those extra few lower degrees cost a lot more to achieve...

The correct sized piston is very important; personally I wouldn't have anything but a TXV metering device on my coil.

Was the airflow checked to be correct; ducts sealed & properly insulated

[ls3c6]

Well, U shouldn't need to get it to 72F to be comfortable.
What's wrong with 74F & 50% RH with air circulation?
Those extra few lower degrees cost a lot more to achieve...

The correct sized piston is very important; personally I wouldn't have anything but a TXV metering device on my coil.

Was the airflow checked to be correct; ducts sealed & properly insulated

The problem is, no matter how much refrigerant you add... the low side pressure never goes above 65-67psi and the superheat will "cycle" from 0-+10 every 1-2 mins.

Another contractor suggests maybe a piece of debris from installation in the orifice/piston and a-coil piston/capilaries need examined?

[udarrell]

The problem is, no matter how much refrigerant you add... the low side pressure never goes above 65-67psi and the superheat will "cycle" from 0-+10 every 1-2 mins.

Another contractor suggests maybe a piece of debris from installation in the orifice/piston and a-coil piston/capillaries need examined?

Possible moisture in the system freezing & thawing...?

It may also have too low an air flow through the coil; resulting in an inadequate heat-loaded coil...

[ls3c6]

well whatever's wrong with it I have to leave it, because everyone else i've called and given the pressures and results to tells me it's probably going to be a waste of $ to come out... run it with the 13f split since humidity's in control or replace the entire system to the tune of $

Since i'll be selling the house in a few years i'll never get a return on that.

[lynn comstock]

... run it with the 13f split since humidity's in control... I believe your humidity number but doubt the accuracy of the 13°F split across the evaporator. (See post 16)

[ls3c6]

Wether you think the split's ok or not, for some reason you can't add refrigerant and get the low pressure side to raise above 65-67... not to mention as it runs the superheat slowly crawls to +10 then works down to 0 and continues this trend.

[lynn comstock]

Wether you think the split's ok or not, for some reason you can't add refrigerant and get the low pressure side to raise above 65-67... not to mention as it runs the superheat slowly crawls to +10 then works down to 0 and continues this trend. A higher pressure means a warmer coil. Fluctuating superheat is a small problem. Zero superheat is not a small problem but one that puts the compressor at risk. Enough said.

[ls3c6]

Right, and i'm trying to get it fixed with no luck.

So as it stands, the system does not respond to a charge and the superheat cannot be stablized.

[ls3c6]

Called another company, they're convinced there has to be an airflow restriction @ the evap coil since head pressure is fine but suction won't increase.

I removed the coil cover and turned the recirculating fan on, it does seem all the air is going AROUND the coil but I don't feel velocity through the coil fins.

The PVC is all glued together and I can't really get it apart so they're going to come next week to remove the coil and clean it

[beenthere]

Try opening the registers to the basement when they are there. it should help to get a steady reading.

The first guy may be doing this for 16 years. But trying to get the vapor above whatever pressure he wanted. Was the wrong way to determine if something is wrong.

[ls3c6]

Well I cut the PVC and pulled the coil out, positioned it 45 degrees and cleaned with a toothbrush... can see completely through it now and in the picture attached was what I removed.

Measuring at air filter and near coil i'm seeing 19.6f, I guess it's ok? Any way to verify the proper blower is installed?

[beenthere]

A good tech can do that, and so far you haven't had a good tech out.

[ls3c6]

is there a NON PERMANANT way to re-seal the PVC evap tube? I've PVC cemeted it all together but i'm leaving one joint free so I can disconnect later if neccesary.

It drips 1 drop per hour currently, can I put plumber's putty around it? I dont' want to have to cut it again to clean the a-coil

[lynn comstock]

190682

[ls3c6]

190682

looking for a substance, not replace any more piping