AC question

[24Carat]

Compare these two outside units, both are considered 2 ton:

A. 3 lbs 4 oz R-22. Pressure differential is 350 high side and 300 low side.

B. 4.5 lbs R-22. Pressure differential is 300 high side and 150 low side. (Neighbor)

Unit B is physically 1/3 larger than unit A.

Which unit will provide cooler and dryer "conditioned" air more economically?

Premise: My townhome apartment has unit A. The humidity will not go below 62% and on a sunny day the inside temp goes up 5 degrees and the unit runs constantly from 10:00 in the morning until 3:00 AM the next morning to pull down that 5 degree climb.

The apartment maintenance crew says the gauge pressures are good and that a temp of 55 degrees at the inside vents is acceptable.

I aimed a water mist at our unit during the heat of the day and my humidity dropped to 55% after 3 days of water mist during the hottest part of the day.

Give me ammo to approach management about how insufficient our compressor unit is.

 

[giovani]

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[giovani]

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[24Carat]

I don't think I was clear. On the Data plate on the corresponding units those are the "design" pressures not gauge readings. My observation is that the 50 point differential on unit A, compared to the 150 point differential on unit B means that A is a cheap POS.




Unit "A"

Unit "B"

 

[danbb]

The design pressures are simply the maximum pressure that the unit can safely take, and has little to no correlation to where gauge pressures would be. It is more for a technician leak testing the system to know how much nitrogen pressure they can safely run up in the system without damaging anything. Do you have the model numbers of the units, and the manufacturer's name and model number off the compressors (black cannonball looking thing in the bottom of the unit)? That will give a better idea of the quality and capacity of the units.

 

[ghitch75]

those are test pressures......the smaller unit is more than likely a 10 seer unit and the larger one is a 13 seer unit......10 older 13 newer......both make 24,000 btu's just one uses less power than the other......as with most apartments is it under sized..... you may need a 30,000 btu(2 1/2 ton) to properly cool the space....

 

[churchmouse]

those are test pressures......the smaller unit is more than likely a 10 seer unit and the larger one is a 13 seer unit......10 older 13 newer......both make 24,000 btu's just one uses less power than the other......as with most apartments is it under sized..... you may need a 30,000 btu(2 1/2 ton) to properly cool the space....

This^^^^^^^^^^^^^^^^^^^^6

The newer 13 seer and higher units have larger evaporators to achieve the efficiency rating. Also the increased fin surface area allows for better de-humidification. As stated above, apartment units are always undersized. If you are on the top floor you get the heat from downstairs and the attic area. The water mist you used just tricks the unit into thinking it is operating in a lower ambient temp and the sub-cooling temp on the liquid refrigerant is reduced. This aids in using more of the evaporator and getting the super-heat down. In short....the unit is happier.
I had to do this on my A/C last year in the 100 plus temps to keep my house comfortable until I stepped up half a ton.

Luck with the front office....most times they do not really care.

 

[24Carat]

Thinking about "cleaning" it after the cooling season with some muriatic acid and forgetting to rinse it off. That will probably cinch future discussions in my favor with the front office management.

 

[churchmouse]

Thinking about "cleaning" it after the cooling season with some muriatic acid and forgetting to rinse it off. That will probably cinch future discussions in my favor with the front office management.

There are other ways but I am not one to tell folks to do wrong..................................

 

[wolfman]

1) Are the coils inside the air exchanger clean? 2) Is the catch pan under the coils full of water? If so you may need to clean the drain, which will help dehumidify the air. 3) Do you have ice forming on the condenser coils blocking air flow?

 

[remauto1187]

1) Are the coils inside the air exchanger clean? 2) Is the catch pan under the coils full of water? If so you may need to clean the drain, which will help dehumidify the air. 3) Do you have ice forming on the condenser coils blocking air flow?

The OP has a register temp of 55 degrees which is 20 degrees plus below the ambient outdoor temp. (Im assuming he was measuring that on one of the last hot days we have had). So that is well within design specs of a split system.
Spraying mist on the condenser actually increases the efficiency of the unit. This is how the manufacturers increase the efficiency of the window units. The blower picks condensation up of the tray area and flings it onto the condenser. The more heat you remove fromt he refrigerant at the condenser the more able it is to pick up heat when it gets to the evaporator.

Sounds like the unit is grossly undersized for the home. Lots of windows and especially large windows let alot sun in which heats the room up and keeps your AC from ever catching up. Blinds, curtains, etc. will help alot!

All else fails, have the neighborhood drunks, friends and dogs pee on the condenser alot, eventually it will eat through the condenser coils and make the unit junk.

 

[24Carat]

1) Are the coils inside the air exchanger clean? 2) Is the catch pan under the coils full of water? If so you may need to clean the drain, which will help dehumidify the air. 3) Do you have ice forming on the condenser coils blocking air flow?

The OP has a register temp of 55 degrees which is 20 degrees plus below the ambient outdoor temp. (Im assuming he was measuring that on one of the last hot days we have had). So that is well within design specs of a split system.
Spraying mist on the condenser actually increases the efficiency of the unit. This is how the manufacturers increase the efficiency of the window units. The blower picks condensation up of the tray area and flings it onto the condenser. The more heat you remove fromt he refrigerant at the condenser the more able it is to pick up heat when it gets to the evaporator.

Sounds like the unit is grossly undersized for the home. Lots of windows and especially large windows let alot sun in which heats the room up and keeps your AC from ever catching up. Blinds, curtains, etc. will help alot!

All else fails, have the neighborhood drunks, friends and dogs pee on the condenser alot, eventually it will eat through the condenser coils and make the unit junk.

The maintenance guys are competent but the conflict is that this place is tasked with making money while doing their damndest to not spend any money, or as little as possible. We have a dog and dog people talk. This place is chocked full of disgruntled residents because of the heat and humidity in their units. I am lucky with having just enough hands on building and equipment experience to end run the bastards and make this place comfortable. It just really erks me that they can so nonchalantly lie to my face and tell me everything is cotton candy and puppy breath.

 

[churchmouse]

The maintenance guys are competent but the conflict is that this place is tasked with making money while doing their damndest to not spend any money, or as little as possible. We have a dog and dog people talk. This place is chocked full of disgruntled residents because of the heat and humidity in their units. I am lucky with having just enough hands on building and equipment experience to end run the bastards and make this place comfortable. It just really erks me that they can so nonchalantly lie to my face and tell me everything is cotton candy and puppy breath.

The way of things these days my friend. If the maint. man tells you the truth he is looking for a job the next day.

I like the pee idea. That will eat up the coil but takes a while to get through the copper.

 

[pwoller]

All windows open and turn the AC on. Let it run that way for a couple of days and I bet they will need to replace it.

 

[24Carat]

In the meantime I get replaced too !

 

[CountryBoy19]

This^^^^^^^^^^^^^^^^^^^^6

The water mist you used just tricks the unit into thinking it is operating in a lower ambient temp and the sub-cooling temp on the liquid refrigerant is reduced.

I wouldn't really say it's "tricking" the unit. That would imply the unit is using some type of smart technology to cool based upon ambient outside temp. What he is actually doing is using 2 different principles to aid in cooling. #1 Upon contant with the condensor the water droplets nearly instantly come up to the temp or the fins/coils, and therefore draw BTU's out of the condensor. #2 As the outside air passes through the now moistened coils they are further cooled by the process of evaporative cooling. This is the same principle that swamp coolers work on. It takes energy to transform liquid water into water vapor. That energy comes by way of reduced temperature. So as the air picks up vaporized moisture from the water mist it drops in temperature and then passes through the coils. This now water laden air requires more BTU to come up in temperature than dry air. That's a lot of words to say, spraying water on your condensor (outside unit) will drop the temperature of the refrigerant. Lower temperature of the refrigerant means that as the air passes through your evaporator (inside unit) it can pull more heat out of the air...

All windows open and turn the AC on. Let it run that way for a couple of days and I bet they will need to replace it.

I highly doubt that will kill the unit. As the OP said, his unit is already running from 10AM-3AM the next day. That is 17 out of 24 hrs in a day. These units are made to run continuous if need-be and running his continuous won't do anything except kill his checkbook when the electricity bill comes around...

 

[churchmouse]

I wouldn't really say it's "tricking" the unit. That would imply the unit is using some type of smart technology to cool based upon ambient outside temp. What he is actually doing is using 2 different principles to aid in cooling. #1 Upon contant with the condensor the water droplets nearly instantly come up to the temp or the fins/coils, and therefore draw BTU's out of the condensor. #2 As the outside air passes through the now moistened coils they are further cooled by the process of evaporative cooling. This is the same principle that swamp coolers work on. It takes energy to transform liquid water into water vapor. That energy comes by way of reduced temperature. So as the air picks up vaporized moisture from the water mist it drops in temperature and then passes through the coils. This now water laden air requires more BTU to come up in temperature than dry air. That's a lot of words to say, spraying water on your condensor (outside unit) will drop the temperature of the refrigerant. Lower temperature of the refrigerant means that as the air passes through your evaporator (inside unit) it can pull more heat out of the air...


I highly doubt that will kill the unit. As the OP said, his unit is already running from 10AM-3AM the next day. That is 17 out of 24 hrs in a day. These units are made to run continuous if need-be and running his continuous won't do anything except kill his checkbook when the electricity bill comes around...

I have been using this "Trick" since 1965 on refrigeration and HVAC units. I see your point but it is tricking the system. Condensing temps fall below what they would be if allowed to run on just the ambient air available to the condenser.

I have done this on evaporation condensing towers as well. Been in this game for a long....long....long time.

Actually too long..................

 

[ghitch75]

I have been using this "Trick" since 1965 on refrigeration and HVAC units. I see your point but it is tricking the system. Condensing temps fall below what they would be if allowed to run on just the ambient air available to the condenser.

I have done this on evaporation condensing towers as well. Been in this game for a long....long....long time.

Actually too long..................

+1.....not back to 65 but to 81......to if you have to wet a condenser you have other troubles that need to be addressed....it can go the other way for you to as to lower the evap. temp to low then it freezes and then no cooling....

 

[24Carat]

+1.....not back to 65 but to 81......to if you have to wet a condenser you have other troubles that need to be addressed....it can go the other way for you to as to lower the evap. temp to low then it freezes and then no cooling....

I don't think freezing will be an issue as the unit is cooling and cycling at a rate I would call "normal". I have a humidistat too and we've seen it drop from 62% to 54% in a matter of a week and that's just running the spray from noon until 6 PM.

If I had the tools and equipment, I thought it would be fun to switch the lines and the 24 VDC between my 10 seer and my neighbors 13 seer unit. Alas, somebody might catch that.

 

[LtScott14]

My Brother in Law bought an older Apt bldg. All the units had working central A/C, unti it got really hot. The upper level units ran constantly, barely cooling.
Downstairs units... worked but marginal.

We found every evap coil plugged solid. Not cleaned in years. We found compressors running with poor capacity- bad valves or overheating from cottonwood jammed into the outdoor condenser.
We scrubbed and cleaned all the stuff. Plugged drains. (units froze from never shutting off.)
Out of six apts: One condenser was replaced, 2 required new Condensor fans, old ones tripped off due to bad motor bearings, the other three ran pretty well after being CLEANED! Actual pressures R22 ran 250#, high side. 75# low side on hot day. Suction lines were wet, and cool on return to condenser.
That is with specs on the unit panels. (inside the unit, not the nameplate readings!)

Moral of story: No Maintenance from previous owner for 10 yrs left the equipment barely running. Cleaning was a major issue and was put off due to the installation without a removal panel to access the evap coils. Crap install. Cheap, save a buck, get in and out.
One renter complained of a hot unit. I checked the temprature on a 95 degree day and was running at 75 degrees. Thermostat read 84. New thermostat and end of complaint.

We had a couple of older window units that we could install in the kitchen, or bedroom if needed. Never used them after working on the stuff.
Churchmouse has seen this for years. Cheap isn't always right.