[KWBum]

Hello. I'm new to this site. Hope you all can help!

So, my house in southern Louisiana is about 3 years old. It was new construction by a builder. That is, it was built for sale, not by a private individual for personal use.

It sat on the market, empty and unoccupied, for about a year and a half. During that time the A/C was run minimally. There is about 600sq/ft upstairs, with it's own A/C, and about 1400sq/ft also with a separate A/C. I'm not sure about the tonnage, but the upstairs is around 2, and the bottom around 3. This is a Carrier system.

Initially, humidity ran about 73% (both by the meter, and by "feel"), especially in the extreme late summer heat. Now it is better, but still not ideal. It is cool and clammy.

I've received an estimate to fix it for about $1000. This involves the following:

1) Clean the coils. Apparently the downstairs needs regular maintenance only. But, the uptstairs plenum or handler has a leak. This caused the blown-in cellulose insulation to get sucked in, and coat the coil.

2) Change the pistons on both. Apparently, for some reason, the pistons are mis-matched. This contributes to the lack of efficiency, and inability to de-humidify.

3) Also, the coils are apparently rusty. That needs to be cleaned.

4) Pipe on outside is very cold. Freon adjustment/reduction was recommended, and will be necessary anyway after piston change.

So, I'm curious as to what people who know a whole lot more than me about A/Cs think about all this.

Thanks! Looking forward to what you all have to say!

By the way...

Tell you what, though, the first estimate I got told me my system was mismatched, and that my conduits, instead of being hung and straight, were simply laid on the floor, and crooked. They offered me two new air handlers (NOT the outside units!), and some conduit straightening, for only $18,000!! :rolleyes:

[NorthernHeat]

Simply put, the equipment is oversized for an energy efficient modernly constructed house. The equipment probably doesn't run long enough to work the humidity out of the air. The contractor may have some information that I don't, but my gut says that they aren't exactly doing all the right things. I would need to know the exact pressures and temperatures to tell you if what they are recommending is right. I also would like to be sure they have the indoor blower speed set right. Good luck.

[KWBum]

You're right, NorthernHeat, detailed info would make a difference.

But I appreciate you gut feelings. I had forgotten about blower speed.

The larger bottom floor has a 3.5 ton unit with an 18 degree differential.
The top floor has a 1.5 ton unit with a 14 degree differential.

When I first moved in I ran both units 24/7 for a few days. It got cold and... clammy.

But like I said, having just bought the place, I'm in no position to spend $18,000 on a new A/C. $1000 is better, but still a lot. I've got to figure out a way to make do with what I've got.

So, any more general hints and/or observations about the above would be great!

[corydec]

What town in Louisiana I might be able to help you I'm from gonzales

[hvac1000]

A great help will be expansion valves instead of the pistons. The manufacturer has kits available for your unit. You might have to ad hard start kit after the change over to expansion valve style control unless your outside condensing units have scroll compressors. Ask the repair people to check on these items.

From your post you have 5 tons of cooling in a 2000 sq ft home. It seems oversized as has already been mentioned. Depending upon how many doors,windows and insulation a more normal size would be 600 sq ft per ton or 3 and 1/2 ton for your size. Here again it depends upon many factors.

There is really no cure when the equipment is this oversize except you might be able to dump/bypass valve some to the basement area to allow for a longer run time upstairs in the conditioned space.

Cutting the blower speed will also help as has been mentioned. Lower speeds will allow the moisture laden air more hang time around the coil and better water extraction. There is also a variable speed motor controller called a fan handler that can be of great assistance with this issue. I also have a diagram to run the AC on a humidistat for speed selection if you would like a copy.

[NorthernHeat]

The 1.5 ton unit has to low of a split. Fan speed is wrong or the charge is incorrect. Head and suction pressures as well as indoor and outdoor ambients could tell us more.

Pistons may also be wrong sizes since many manufacturers don't actually make a 1.5 ton coil, they just change the piston in the 2 ton coil same with all the other 1/2 ton sizes. 3.5 ton uses a 4 ton coil with a different piston and so on.

[KWBum]

Humidity in New Orleans averages 87% day, 65% night. Year-round!

None of the contractors who've looked at the units so far mentioned neither 1) an expansion valve, nor 2) slowing down the blower speed.

But, if the pistons are in fact mismatched, would an expansion valve even work? Especially if the pistons are not replaced and properly matched?

But this seems reasonable, given what I've read. That is, installing an expansion valve, and maybe the hard start kit.

I wonder how much more efficient it would make the A/C? Hopefully not be too expensive.

The fan handler is also reasonable. It makes sense in terms of how an A/C gets the moisture out of the air. And, it would seem to be a way to make what I have more efficient. Again, cost would be a big consideration.

The humidistat is interesting. But, I don't know. I ran the A/C continuously for days. It got cooler, but still humid.

In general, the system is gets easily overwhelmed by high outside temperatures, and high outside humidity.

But I really do appreciate all this help!

[KWBum]

Apart from everything else, the 1.5 ton unit apparently has a coil coated with cellulose insulation. There's a hole in there somewhere sucking the insulation and gumming up the coils.

I run the thing at 78-79. Outside it's been 91-95d/75n.

So, it could possibly be the pistons?

Would the expansion valve simply by-pass the piston problem? (Then again, it might need the hard start.) But, if the expansion valve is an option, what's the better solution? Piston? Or valve?

And how much should such repairs cost?
To change out the pistons on two units? Or to put in an expansion valve? Finally, to adjust the blower speed?

[KWBum]

hvac1000, thank you for your offer of the diagram! I'd love to take a look at it, but it sounds like something geared more towards a professional A/C person...

[hvac1000]

((Would the expansion valve simply by-pass the piston problem? (Then again, it might need the hard start.) But, if the expansion valve is an option, what's the better solution? Piston? Or valve?))

The expansion valve replaces the piston. You toss the piston away when you use the expansion valve. You will get much tighter control over the entire refrigerant system with a expansion valve.

As I mentioned before if the compressors are not scroll design and are reciprocating type you will need hart start kit. The fan controler will help the unit suck the water right out of the air by adjusting the blower speed to the moisture load. Then when the moisture is lowered it will go to a higher speed to increase the cooling. It is a smooth ramp up and down. You will never know it is operating and actually most of the time the blower speed is lower so it is actually quieter.

[wheatnbarley24]

The units are sized properly for this area, you also have to take into account the ceilings heights, if they are taller than the average 8 feet ceiling you are cooling that much more cubic feet

[KWBum]

So, basically, it looks like everyone feels that having the pistons changed is not the best idea.

I need to ask the technician about a couple of things:

1) The expansion valve, and possibly a hard start kit.
2) A fan handler. Possibly hooked up to a humidistat.

But, just so I have an idea, how much do you all think this work should cost?

That is, how much should the pistons cost on the two units.
And, how much should expansion valves and fan handlers for two units cost?

Thank you all for all the advice!

[KWBum]

the units are sized properly for this area, you also have to take into account the ceilings heights, if they are taller than the average 8 feet ceiling you are cooling that much more cubic feet

Very good point. I forgot to mention that all the downstairs, and most of the upstairs, has 10' ceilings!

[wheatnbarley24]

I think a simple and cheap humidistat which would be mounted in your return air is the best solution to your problem

[NorthernHeat]

Tell me once again what a humidistat is going to do for this problem.

If an A/C won't dehumidify it is almost always wrong air speed or oversized. The fact that he says it cools very well and the air is still clammy spells oversized. If it was undersized it wouldn't achieve desired temp', but he says it will.

"When I first moved in I ran both units 24/7 for a few days. It got cold and...clammy. "

Maybe an Aprilaire whole house dehumidifier installed for aprox 1000 dollars might be the simplest and cheapest thing in the long run.

[KWBum]

I was actually thinking about the Ultra-Aire 90H by Therma-Stor.

But the final question is, would leaving the pistons as they are, mis-matched, and installing a TXV and the variable speed fan handler make any difference?

[wheatnbarley24]

The humidistat would be wired in with a relay which would override the thermostat making the unit run at a lower fan speed until desired humidity setting is reacher(may over shoot set point by a couple degrees but I think they would sacrifice that much)

[KWBum]

So, if I'm understanding all of this correctly, the main issue is the fan speed?

I need to get the fan to run at the right speed, for the right time, to remove the humidity.

That is, I shouldn't worry about the pistons, or about installing a TXV?

Also, the whole-house dehumidifier would be overkill?

[T-Top]

Tell me once again what a humidistat is going to do for this problem.

If an A/C won't dehumidify it is almost always wrong air speed or oversized. The fact that he says it cools very well and the air is still clammy spells oversized. If it was undersized it wouldn't achieve desired temp', but he says it will.

"When I first moved in I ran both units 24/7 for a few days. It got cold and...clammy. "

Maybe an Aprilaire whole house dehumidifier installed for aprox 1000 dollars might be the simplest and cheapest thing in the long run.

I agree with NorthernHeat If the blower is set on to high of speed giving you quick cycles, it will not remove the humidity. A Thermidistat on a variable speed blower will make the blower run on its lowest possible speed with out freezing up the evap coil. As far as changing the piston size to remove the humidity, the only thing you get is the wrong size metering devise for your system.

[acetc]

I agree with HVAC1000, you replace the two pistons with thermostatic expansion valves and slow the blower speeds down to achieve a temperature differential of 20 to 22 degrees across the coil, and absolutely find and fix the hole in the duct so that at least you are not pulling in attic air (hot and humid) and clean the coil to provide good heat transfer. It should not cost more then $1000 for every thing, shop around. The bid for $18000 is a joke, I could fly there for a week fix your problem, have a vacation and smile all the way to the bank. Best of luck to you, Mike