ac settings

[Like_Fry]

My GF’s genius roommate made yet another wonderful proclamation today. She stated that you will wear out the AC by turning it down below 72 deg F. I for one have never heard that. I can understand it might wear the fan motors more, but is it really that significant?

We are asking since this is a 3 story row house, and of course we sleep on the 3rd floor, and the roommate sleeps in the bedroom on the 1st floor (yes it took her a month to figure out she could close the vents in her room. Needless to say, it gets hot upstairs, even with the AC on. The thermostat is on the 2nd floor.

So what happens, is we suffer upstairs, sweltering (around 80 deg F), and then the roommate, who usually stays at her BF’s, comes home in the morning, and turns it up to 75 or so (she used to turn it off). My poor GF gets up and the whole place is getting hot, so she turns it back to 70, which is where she left it.

The other thing we are concerned about, which is why its also set at 70, is the puppy, who is a large breed, and they arent supposed to like heat (when the roommate has turned it up, the puppy starts sleeping out of her crate, and gets antsy.

Anyway, what is the ideal setting for the AC, and shouldnt it be left on one specific setting so it doesnt strain the system?
Thanks,

Fry

[Joey_P]

[QUOTE=Like Fry]

Anyway, what is the ideal setting for the AC, and shouldnt it be left on one specific setting so it doesnt strain the system?
Fry
[/QUOTE]

Wheather you keep it at one setting or not won’t make a difference as far as ‘straining’ the system is concerned. The thermostat is just a glorified on/off switch.
As for the temp setting, set whatever is comfortable to you, yeah, the lower you set it, the harder (read: more) it has to work, but the AC unit itself doesn’t know what temp you set it to. That is to say, wheather you set it to 80 or 60 it still sends the freon to the evap coils at the same temprature. The only differnce is that at 60, the tstat will wait longer before it tells the AC to shut down.
The main problem you’ll have with setting the temp lower (other then extra wear and tear on various parts) is that if it runs too long on a really humid day, you can wind up icing over the evap coils and that can cause problems, but as long as you don’t notice a reduction in the amount of air coming though the vents you should be safe. With the temp set higher, the AC will spend less time running and that gives any accumulated ice more time to thaw and drip off.
Oh, and as for 72 degrees being some magical number at which point bad things will happen, it sounds arbitrary to me…ask for a cite.

[Tim_T-Bonham.net]

[QUOTE=Joey P]
Oh, and as for 72 degrees being some magical number at which point bad things will happen, it sounds arbitrary to me…ask for a cite.
[/QUOTE]
Utterly arbitrary. Any such real statement will talk about the temperature difference between the current temp and the setting temp. Setting to 72º when it’s 95º outside is a lot different than when it’s 70º outside.

But people who make statements like this don’t know what cites are (and don’t really believe in such things anyway).

[Philster]

If you can, run the ‘fan’ on the A/C unit by moving the fan switch at the thermostat to ‘on’ instead of ‘auto’. It is great technique for balancing the temps at night on multiple stories and will definitely save $ by discouraging use of the compressor (which you prompt to come on by lowering the temp setting).

When the compressor is off, the fan will then continue to move air around, pulling in air from the returns and better balancing the temps up and down. It will sound like the A/C is on (because you will hear the fan running), but the costly compressor is not running.

This will keep you from forcing down the master temp to make the A/C run to satisfy your desire to get fresh cool air upstairs.

With vents closed downstairs and air being exhanged by the fan, you’ll be much closer to finding a happy thermostat setting.

[Like_Fry]

Thank you all for the great answers. My GF is going to ask her roommate where in the world she got her info from.
This morning she turned it to 75 again, and then left, I have words for this, but it would have to be in the pit.

I must admit, I took the liberty of “adjusting” the thermostat, so 75 now is more like 70. We are hoping this will solve the issue. (yes I know this is a bit jerkish)
Fry

[Hampshire]

Sounds like she got started in the right direction by closing the vents in her room but you could go a step further and close all the vents on the 1st and 2nd floors. Hot air rises and cold air sinks as you are probably well aware so pumping cold air to the top of the house and letting it trickle down works well.
The other problem you need to solve is pumping hot air out of the top of the house when it’s trapped there. Attic fans can do this but if you don’t have one you may need to open a window during the night.

[raindog]

[QUOTE=Joey P]
Wheather you keep it at one setting or not won’t make a difference as far as ‘straining’ the system is concerned. The thermostat is just a glorified on/off switch.
As for the temp setting, set whatever is comfortable to you, yeah, the lower you set it, the harder (read: more) it has to work, but the AC unit itself doesn’t know what temp you set it to. That is to say, wheather you set it to 80 or 60 it still sends the freon to the evap coils at the same temprature. **The only differnce is that at 60, the tstat will wait longer before it tells the AC to shut down. **
[/quote]

I’m not so sure. As you noted, problems could occur. A standard A/C system for human comfort needs Btus across the evaporator to evaporate or boil all the refrigerant before exiting the evaporator. (Freon enters the evaporator as a liquid and leaves as a vapor)

If you set your tstat at 60° you will end up removing so much heat from the structure that there isn’t enough heat content left in the air stream to evaporate all the refrigerant. So…the compressor gets back a combination of liquid and vapor.. But your compressor is a vapor pump, and liquid refriferant will damage the compressor. This repair can be very expensive.

While not damaging to the compressor every time, if left like this it will damage the compressor more times than not. Setting the tstat at 60° is asking for a very expensive repair. I advise to never set a stat below 65°, and better yet, 68°. (and 68° is darn cold for A/C)

The main problem you’ll have with setting the temp lower (other then extra wear and tear on various parts) is that if it runs too long on a really humid day, you can wind up icing over the evap coils and that can cause problems, but as long as you don’t notice a reduction in the amount of air coming though the vents you should be safe. With the temp set higher, the AC will spend less time running and that gives any accumulated ice more time to thaw and drip off.
Oh, and as for 72 degrees being some magical number at which point bad things will happen, it sounds arbitrary to me…ask for a cite.

This is partially true, but the icing doesn’t come from humidity. (which would have the effect of raising pressures and would work against icing the coil) In this context, the icing would be a result of removing too much heat from the structure. (as explained above) Compressors are durable machines and will take a fair amount of abuse before they die, but running liquid through them is bad news. If the suction line is well insulated the homeowner may never know----or be able to see—that the evaporator and compressor (which is housed in the condenser) are iced up.

My .02¢: 65° is iffy, but may be OK. 68° is better. 60° will in time cause damage. (and maybe a short time!)

[Joey_P]

I tend to forget that alot of my (second hand) knowledge about AC comes from commercial cooler/freezers. Correct me if I’m wrong, but I beleive they have a solonoid (or a valve maybe) that circulates liquid freon around the compressor.

Also, I’m not sure if this is what you were referring to or not, but when I mentioned a ‘very humid’ day, I meant to imply that it was humid enough that the inside air was damp as well. Wouldn’t that cause the evap coils to ice up? And if the ice doesn’t come from humidity, what causes it? A hot humid day will keep the AC running longer, but a dry hot day and it won’t have any moisture to condensate.

BTW I’m not debating you on any of these points. I’ve always been interested in HVAC. For years I’ve been meaning to go and take some HVAC classes and get my EPA certification so I can do more work on my own units. Currently I’m running 12 (soon to be 13) coolers and freezers. Over the years I’ve learned ALOT about how to fix them* via the internet, asking around or following the repair guy around.

*Since I can’t do anything involving freon, I’ve always heard the terms thown around (high side, head pressure etc) but never really learned anything about it. Acutally, one of our repair guys told me that with how much I already know about fixing the units, I should get a set of guages and learn how to use it. That way I could pin point the problem and give his dispatcher a better idea of what’s wrong before they send him out. But I digress.

[raindog]

[QUOTE=Joey P]
I tend to forget that alot of my (second hand) knowledge about AC comes from commercial cooler/freezers. Correct me if I’m wrong, but I beleive they have a solonoid (or a valve maybe) that circulates liquid freon around the compressor.

Also, I’m not sure if this is what you were referring to or not, but when I mentioned a ‘very humid’ day, I meant to imply that it was humid enough that the inside air was damp as well. Wouldn’t that cause the evap coils to ice up? And if the ice doesn’t come from humidity, what causes it? A hot humid day will keep the AC running longer, but a dry hot day and it won’t have any moisture to condensate.

BTW I’m not debating you on any of these points. I’ve always been interested in HVAC. For years I’ve been meaning to go and take some HVAC classes and get my EPA certification so I can do more work on my own units. Currently I’m running 12 (soon to be 13) coolers and freezers. Over the years I’ve learned ALOT about how to fix them* via the internet, asking around or following the repair guy around.

*Since I can’t do anything involving freon, I’ve always heard the terms thown around (high side, head pressure etc) but never really learned anything about it. Acutally, one of our repair guys told me that with how much I already know about fixing the units, I should get a set of guages and learn how to use it. That way I could pin point the problem and give his dispatcher a better idea of what’s wrong before they send him out. But I digress.
[/QUOTE]

I should have been clearer. Sorry.

The humidity is the “source” of the ice, but the humidity, in an of itself, doesn’t cause the ice.

The cause of the ice is found in the pressure-temperature relationship. (found everywhere in nature and elsewhere)

The “low” side or “suction” side (the blue gage) of an A/C system for human comfort cooling has an evaporator coil temp of around 40°; that means that the coil is 40° and as warm air-----laden with water vapor (humidity)----- passes over it the water vapor condenses to water; called condensation, or, condensate. So far so good.

At 40°, the water will not freeze. it runs down the drain. However…if the coil temperature gets to 32°, or colder, the condensate now turns to frost. The frost acts as an insulator and creates a rapid spiral. Soon, it’s not frost but ice.

Here’s where the pressure-temperature relationship comes in. Anything that represents a “load”—heat— would elevate the pressure in the coil. So…higher temperatures create higher pressures. Humidity is one such load; it’s “latent” heat—heat that can’t be read on a thermometer. (as oppsed to another load; “sensible” heat, that can be read on a thermometer) At any rate, the higher the load, the higher the pressures.

Now most A/C systems (for now) use R-22 or “Freon.” It is the nature of the chemical properties of Freon that [around] 58 psi corresponds to 32°.

When the house is hot this heat*, or load*, elevates the pressure in the evaporator—and the temperature. The pressure stays above 58psi and any condensate stays water. Humidity is such a load and serves to keep the pressure and temerature up—above 58psi.

The problem with a setpoint of 60° is that as you remove more and more[ latent and sensible] heat the pressure (and the subsequent temperature!) in the evaporator falls. There is less and less heat content----in any form; latent or sensible----in the air stream. So…the pressure falls below 58psi and any humidity will now begin to freeze. (because the coil is now colder than 32°)

Most A/C sytems for humans operate with evaporator pressures between 60 and 70 psi. With Freon, this corresponds to 33° to 40°. The heat in the house is needed; it’s part of the design. The system is designed for a certain amount of “load” imposed on the evaporator. In fact, the engineers calculate both the latent load, and the sensible load, the evaporator needs to see to operate correctly.

When you run the stat down to 60° you’re effectively outside design conditions. There is not enough heat or load imposed on the evaporator to keep the pressure above 58psi, and the temperature falls below 32°; the point in which any additional humidity will not condense, but freeze.

I don’t know if this makes any sense, but it’s the best I can do. :o

[Joey_P]

[QUOTE=the raindog]
I should have been clearer. Sorry.
[/quote]

You were fine, you had no idea this would become a lesson.

At 40°, the water will not freeze. it runs down the drain. However…if the coil temperature gets to 32°, or colder, the condensate now turns to frost. The frost acts as an insulator and creates a rapid spiral. Soon, it’s not frost but ice.

I think we have to come back to this part.

Anything that represents a “load”—heat— would elevate the pressure in the coil. So…higher temperatures create higher pressures.

I assume the pressure goes up becuase of the extra heat being removed from the air? More heat being removed=hotter freon gas=higher pressure

Humidity is one such load; it’s “latent” heat—heat that can’t be read on a thermometer. (as oppsed to another load; “sensible” heat, that can be read on a thermometer) At any rate, the higher the load, the higher the pressures.

The humidty condensing on the coils creates heat, right? For the same reason the cond coils are warm, correct…in principle that is. When something condesnes it gives off heat. So the water vapor condenses, gives off a little heat, and the coils absorbs the heat.

The problem with a setpoint of 60° is that as you remove more and more[ latent and sensible] heat the pressure (and the subsequent temperature!) in the evaporator falls. There is less and less heat content----in any form; latent or sensible----in the air stream. So…the pressure falls below 58psi and any humidity will now begin to freeze. (because the coil is now colder than 32°)

This would be the spiral you were referring to. Let me get this stright. You set the temp too low, there’s no heat left for the system to remove, so the evap coils get way colder then they need too, therefore freezing over. Once they freeze over, air doens’t circulate etc etc etc. Right so far?

Okay, I think I’m starting to understand the pressure thing better.

So there is a ‘magic’ number. Of course it’s not the number the AC is set to. It’s the number the house temp shouldn’t fall below. You could set your tstat at 40 degrees, but as long as the house temprature never goes below 60(?), you’ll be safe.
Now, I assume that the same problem would happen on a dry day, but it would just take a lot longer without the ice buildup.

Now, why do the cond coils need to have a little heat on them all the time? On our big units that have two fans the coils, one is always running and the other only comes on during the hot summer days. We had problems a while ago with them both running all the time, something about head pressure. The result was that our cooler warmed up a few degrees. Nevermind, don’t answer that, I don’t want to hijack the thread more then it is already.

[Rick]

[QUOTE=the raindog]
I’m not so sure. As you noted, problems could occur. A standard A/C system for human comfort needs Btus across the evaporator to evaporate or boil all the refrigerant before exiting the evaporator. (Freon enters the evaporator as a liquid and leaves as a vapor)

If you set your tstat at 60° you will end up removing so much heat from the structure that there isn’t enough heat content left in the air stream to evaporate all the refrigerant. So…the compressor gets back a combination of liquid and vapor.. But your compressor is a vapor pump, and liquid refriferant will damage the compressor. This repair can be very expensive.

While not damaging to the compressor every time, if left like this it will damage the compressor more times than not. Setting the tstat at 60° is asking for a very expensive repair. I advise to never set a stat below 65°, and better yet, 68°. (and 68° is darn cold for A/C)
[/quote]
First off liquid is not compressible. So any liquid getting back to the compressor will do damage. However the engineers that design these systems are not idiots

It is designed so well that a lot of “cooling effect” is still left in the refrigerant as it returns back into the compressor and this cools off the hot motor windings and mechanical parts just before it gets compressed again to start the new cycle though the system. But, it is designed so well that no liquid is left to dump into the compressor, because liquid will not compress and it would break the valves inside the compressor. You see, now, that the pieces all have to fit together just right like the manufacturer planned it.

cite

This is partially true, but the icing doesn’t come from humidity. (which would have the effect of raising pressures and would work against icing the coil) In this context, the icing would be a result of removing too much heat from the structure. (as explained above) Compressors are durable machines and will take a fair amount of abuse before they die, but running liquid through them is bad news. If the suction line is well insulated the homeowner may never know----or be able to see—that the evaporator and compressor (which is housed in the condenser) are iced up.

My .02¢: 65° is iffy, but may be OK. 68° is better. 60° will in time cause damage. (and maybe a short time!)

This is incorrect. Icing is caused by two things. Humidity and too cold an evaporator temp. If you have both of these, the evaporator will ice. You do not have to remove too much heat from the system, if the evaporator is cold enough, it will ice if there is humidity present.

[raindog]

[QUOTE=Rick]
First off liquid is not compressible. So any liquid getting back to the compressor will do damage. However the engineers that design these systems are not idiots cite
[/quote]

Not true. While liquid is not compressible the average compressor (hermetic recips and scrolls) will take liquid for months in many cases before damage. It is a crap shoot, however, and I’ve seen compressors go the first time they’re slugged. (hence the use of crankcase heaters)

So…while “any liquid” may cause damage—and it certainly bad for a compressor,—(read my posts, K?) it is not true that “any liquid” will damage them. I see compressors every day with fixed orifice metering evaporators that are overcharrged, or that have clogged filters or bad blowers or dirty coils or, or, or…and liquid is being fed to the compressor. In time, all compressors will be damaged if liquid is run through them. Some of them will be damaged the first time they see liquid (particulalry at start up); others m,ay have liquid run through them for weeks and still be OK once they’re fixed.

This is incorrect. Icing is caused by two things. Humidity and too cold an evaporator temp. If you have both of these, the evaporator will ice. You do not have to remove too much heat from the system, if the evaporator is cold enough, it will ice if there is humidity present.

Apparently you didn’t take the time to read my posts in their entirety, or even at all. Read it again.

How do you get “too cold an evaporator temp”? When within design conditions—which includess proper sizing, airflow and sufficient load on the evaporator among others—the evaporator will be within 60 and 70psi. With R-22 that is between 33 and 40 °.

So your answer is incorrect. If there is a heavy load on the evaporator it will not ice up! Hell, there doesn’t even need to be a heavy load; there only needs to be design load—and the evaporator will be above 60 psi. Based on the P/T relationship of R-22, the coil will be above 32° and water/condensate will not freeze. Hence my comment:
*
"The humidity is the “source” of the ice, but the humidity, in an of itself, doesn’t cause the ice.

The cause of the ice is found in the pressure-temperature relationship. (found everywhere in nature and elsewhere) "*

It is all in the pressure/temperature relationship. If the evaporator has design load, you cannot have “too cold an evaporator temp.”

So, humidity is not the “cause” of icing. It is the “source”, but not the cause. Low load on the evaporator—not enough heat on the evaporator, is the cause of freezing. (low refrigerant charge being another; but this too is due to the P/T relationship)

(Incidentally, that cite was one of the worst written explanations of the refrigeration cycle I’ve ever seen)

[raindog]

[QUOTE=Joey P]

I assume the pressure goes up becuase of the extra heat being removed from the air? More heat being removed=hotter freon gas=higher pressure
[/quote]
Exactly.

The humidty condensing on the coils creates heat, right? For the same reason the cond coils are warm, correct…in principle that is. When something condesnes it gives off heat. So the water vapor condenses, gives off a little heat, and the coils absorbs the heat.

Well, kinda. The water vapor, (humidity) which is a form of heat. The cold evapoator coil accepts the Btus, and in the process the Btus are transferred to the Freon. Because the coil is below the dew point, the water[vapor] in the moist air is condensed to water. The air is “dried out.”

This would be the spiral you were referring to. Let me get this stright. You set the temp too low, there’s no heat left for the system to remove, so the evap coils get way colder then they need too, therefore freezing over. Once they freeze over, air doens’t circulate etc etc etc. Right so far?

Exactly. Anything that reduces the load on the evaporator has the potential to lower the pressure (and therefore the temperature!) and cause the evaporator to ice up. Too low a setpoint may cause this—too much heat removed from the air stream. The most common causes are dirty filters, dirty coils, too many closed registers, a faulty blower motor etc. You’ll note that each of these examples are things that reduce airflow—and in the airflow is heat; load.

So there is a ‘magic’ number. Of course it’s not the number the AC is set to. It’s the number the house temp shouldn’t fall below. You could set your tstat at 40 degrees, but as long as the house temprature never goes below 60(?), you’ll be safe.

I think you’re right. I don’t know if that number is 60°, or 62°, or 56°; but you’re right that at some point an evaporator will ice up if there is insufficient load to keep pressures above 60psi/32°.

Now, I assume that the same problem would happen on a dry day, but it would just take a lot longer without the ice buildup.

This is true in theory. Of course, theres always some humidity in the air, right? So we never get to 0% RH. But you are right. The ice is NOT the cause of icing. But on a dry day there will be less water vapor, and therefore less condensate. Still, if your evaporator is colder than 32° (which is a function of the P/T relationship, and with R-22 corresponds to about 58psi) any humidity in the air will not condense to water and stay water. It will condense and promptly freeze.

Now, why do the cond coils need to have a little heat on them all the time? On our big units that have two fans the coils, one is always running and the other only comes on during the hot summer days. We had problems a while ago with them both running all the time, something about head pressure. The result was that our cooler warmed up a few degrees. Nevermind, don’t answer that, I don’t want to hijack the thread more then it is already.

[Joey_P]

Thank you.

One of the 'great mysteries" to me was why low freon caused the blowers to ice up. It always seemed to me that low freon, meant less cold and therefore the cooler should start warming up. I never would have guessed that less freon means more cold (which means ice, which means no air movement, which means the cooler starts warming up, which means the tstat keeps everything running, which means more ice…) and more freon meant less cold. But like I said (until now) I never even bothered to learn anything about freon. Don’t get me wrong, I have a basic understading of the cycle, but since, legally, I can’t do anything with it, I spent my time learning about the electrical side.

[Joey_P]

One more thing, when freezer coils ice over, that would be soley do to humidity, correct? Since 32 degrees is well within the temprature range they are designed to handle.

Any will you come and take all the product off the bottom shelf of my three door freezer and find out why my door heaters are shorted out? Cuz I don’t wanna do it again.)

[CookingWithGas]

[QUOTE=Hampshire]
The other problem you need to solve is pumping hot air out of the top of the house when it’s trapped there. Attic fans can do this but if you don’t have one you may need to open a window during the night.
[/QUOTE]
I disagree with this if you are using air conditioning. An attic fan blows air out of the house, which means air has to come in somewhere to replace it. That means hot outside air. The attic should be insulated so that hot air in the attic is not a big issue. Opening a window when the A/C is running is also self-defeating.

Every floor should have air returns (a townhouse may just have one per floor) that sucks the air back down to the A/C unit to re-cool it, so hot air should not be getting trapped on the top floor.

Also, closing vents on the lower floors is fine, but what works even better is adjusting the louvers in the ducts near the A/C unit, if you have louvers. You can see levers on the sides of the big ducts that leave the A/C unit. You can close off an entire area of the house that way.

Another strategy, in addition to closing vents, is closing off returns on the lower floor to create more suction in the returns on the top floor. I don’t know if an HVAC pro would agree with that, but it’s worked for me.

[raindog]

[QUOTE=CookingWithGas]
I disagree with this if you are using air conditioning. An attic fan blows air out of the house, which means air has to come in somewhere to replace it. That means hot outside air. The attic should be insulated so that hot air in the attic is not a big issue. Opening a window when the A/C is running is also self-defeating.

Every floor should have air returns (a townhouse may just have one per floor) that sucks the air back down to the A/C unit to re-cool it, so hot air should not be getting trapped on the top floor.

Also, closing vents on the lower floors is fine, but what works even better is adjusting the louvers in the ducts near the A/C unit, if you have louvers. You can see levers on the sides of the big ducts that leave the A/C unit. You can close off an entire area of the house that way.

Another strategy, in addition to closing vents, is closing off returns on the lower floor to create more suction in the returns on the top floor. I don’t know if an HVAC pro would agree with that, but it’s worked for me.
[/QUOTE]

You may be thinking of a “whole house fan” instead of an attic fan. A whole house fan is located in the ceiling and draws air from outside and discharges it into the attic. It basicaly pulls air through the [open] windows [and blows it into the attic.] And you should never run a whole house fan with the A/C on. With the WHF running you’re air conditiong the neighborhood. It won’t work.

An attic fan is another matter. It is almost always a good idea. Rather than the ceiling, it is mounted on the roof. Where a whole house fan is designed to ventilate the house, an attic fan is designed to ventilate the attic. The attic fan draws it’s “make up” air from ridge vents in the roof, vents cut into the roof, or soffit vents. Reducing the attic temperature from 115+° (common) to 100° takes a HUGE load off the A/C system. And the energy to run them is much less that the energy used in running the A/C. IME/IMO most every home should have an attic fan.

[Napier]

FWIW I’ve been running a $80 window air conditioner flat out for over a year now and it still works.

I have a humidity problem in my house and am trying to provide a little fresh air for a special contamination control problem. It’s a long story. But I fixed something by attaching a duct thimble (which is a fitting) onto the cold air output of the AC and then hanging the whole damn assembly outdoors under a fairly high deck. It’s not in a window, it’s just sucking outdoor air over both coils and hanging on 4 chains and 2 support bars. I set the fan on low and turned the thermostat all the way cold. During most of the summer months the compressor runs 24/7. The duct fitting is connected to a small duct that runs into my basement. Depending on conditions, a temperature probe attached inside the cold air duct fitting on the AC reads about 15 or 20 °C below the outdoor temp, but bottoms out at around 0.5 °C if the outdoor temp is low enough. The coil never ices. I think there must be some pretty accurate temp limit circuit that cuts the compressor to prevent icing. Also, during winter months I don’t change any settings, but the compressor doesn’t run. As a result, my basement is always cool and dry, and some air I also pump from the basement up into my bedroom is quite dry. I generally keep the bedroom around 23 °C and 40% RH in the summer, and drier in the winter.

[raindog]

[QUOTE=Napier]
FWIW I’ve been running a $80 window air conditioner flat out for over a year now and it still works.

I have a humidity problem in my house and am trying to provide a little fresh air for a special contamination control problem. It’s a long story. But I fixed something by attaching a duct thimble (which is a fitting) onto the cold air output of the AC and then hanging the whole damn assembly outdoors under a fairly high deck. It’s not in a window, it’s just sucking outdoor air over both coils and hanging on 4 chains and 2 support bars. I set the fan on low and turned the thermostat all the way cold. During most of the summer months the compressor runs 24/7. The duct fitting is connected to a small duct that runs into my basement. Depending on conditions, a temperature probe attached inside the cold air duct fitting on the AC reads about 15 or 20 °C below the outdoor temp, but bottoms out at around 0.5 °C if the outdoor temp is low enough. The coil never ices. I think there must be some pretty accurate temp limit circuit that cuts the compressor to prevent icing. Also, during winter months I don’t change any settings, but the compressor doesn’t run. As a result, my basement is always cool and dry, and some air I also pump from the basement up into my bedroom is quite dry. I generally keep the bedroom around 23 °C and 40% RH in the summer, and drier in the winter.
[/QUOTE]

I’m not sure I entirely understand what you’ve done. Are you using this as a dehumidifier?

The part I don’t fully understand is the part about running the air over both coils. (??)

[Dag_Otto]

[QUOTE=the raindog]
I’m not sure I entirely understand what you’ve done. Are you using this as a dehumidifier?

The part I don’t fully understand is the part about running the air over both coils. (??)
[/QUOTE]

It sound to me like it is a 100% outside air application with no humidity control.