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DarkLogix
Texan and Proud
Premium
join:2008-10-23
Baytown, TX
kudos:3

[HVAC] Issue with AC

seems when its cold out (sub 40F) my split mini AC unit can't run its compressor

due to this my room quickly gets hot when its cold out. (servers and other computer equipment)

is there anything that can be done or should I just turn the AC off when temps drop (kinda rare) and be forced to leave my door open?

Might look into getting a new screen for my window and just opening that.
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Dodge
Premium
join:2002-11-27
There are some units designed to work in very low temperatures. For example: »www.ajmadison.com/cgi-bin/ajmadi ··· SV2.html (down to 14F). We have a mitsubishi in our office that cools a server room, that's been working 24/7 for a few years regardless of temperature.


DarkLogix
Texan and Proud
Premium
join:2008-10-23
Baytown, TX
kudos:3
Well replacing the unit is out of the question, so would it be possible to have the people that installed it do something so that it would keep working at low temps?
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iknow_t

join:2012-05-03
said by DarkLogix:

Well replacing the unit is out of the question, so would it be possible to have the people that installed it do something so that it would keep working at low temps?

that can be done, but it would be sort of like running a car without oil!. not good..

flaughs2000
Premium
join:2004-02-07
East Freedom, PA
reply to DarkLogix
You need a "Low Ambient Kit" installed.

Scroll do to Will's answer i did not want to steal from yahoo.com
»answers.yahoo.com/question/index ··· 1AAhsGSR


LazMan
Premium
join:2003-03-26
canada
reply to DarkLogix
Make and model of the system?

Odds are good your options are replace, or live with it; but need more info to be sure...


Cho Baka
Premium,MVM
join:2000-11-23
there
kudos:2
reply to DarkLogix
Open the window seems like a winner to me...
--


Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:2
Reviews:
·Callcentric
reply to DarkLogix
Click for full size
Here's what I have: »www.icmcontrols.com/Head-pressur ··· iew.html

It's a head pressure control module. It comes with a thermocouple to monitor your line temperatures. It slows down the outside fan motor according to the temperature of the refrigerant so that the pressures do not drop too low when trying to run your AC in the winter. What may be happening is that you are overcooling your refrigerant which is causing your compressor turn off due to a low pressure cut-off switch.

A head pressure control will vary the fan speed according to inside load and outdoor temperature conditions. This will keep your pressures up where they should be and will protect your compressor from damage when running the AC in the winter. If you try to run an AC when it's cold outside it cools the refrigerant too well which can cause the refrigerant to become a liquid before it gets to the compressor. This liquid refrigerant is non-compressible and can cause damage. The liquid will also wash the oil off the motor bearings. Both will lead to premature failure. A head pressure control can prevent that...


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Reviews:
·Comcast
reply to DarkLogix
Have you considered putting a through the wall fan in the wall to push some of the excess heat from your room to the rest of the house?

Depending on the configuration of the ceiling and space above, a fan induced jumper duct also may be able to pull the heat from the ceiling in your room to an adjacent area.

If it is that cold outside, they may appreciate some of the waste heat you are generating.
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The difference between genius and stupidity is that genius has its limits.


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
kudos:3
reply to LazMan
said by LazMan:

Make and model of the system?

Odds are good your options are replace, or live with it; but need more info to be sure...

Daikin ftxn12jevju/c001015
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cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to Cho Baka
If it's a real server room then there are no windows.


Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:2
Reviews:
·Callcentric
reply to DarkLogix
said by DarkLogix:

Daikin ftxn12jevju/c001015

OIC... head pressure control will not work considering you have only one fan motor. You could put cardboard over part of the outdoor coil to restrict (but not completely block) airflow.

Another option could be to install a room ventilation fan to pull in cold air from outside. Then you could hook it up to a cooling thermostat to automatically turn on when your room needs cooling.


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
kudos:3
said by Sly:

said by DarkLogix:

Daikin ftxn12jevju/c001015

OIC... head pressure control will not work considering you have only one fan motor. You could put cardboard over part of the outdoor coil to restrict (but not completely block) airflow.

Another option could be to install a room ventilation fan to pull in cold air from outside. Then you could hook it up to a cooling thermostat to automatically turn on when your room needs cooling.

So any solution for this unit?
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Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:2
Reviews:
·Callcentric
I did some more reading and it seems like the cardboard over the coil idea wasn't that far off... They seem to sell an optional wind baffle that will let it operate down to 0°F. Although I haven't found it for sale online anywhere.

It seems that your system has an outdoor temperature sensor that automatically turns off at 40°. According to page 39 of the manual, you place the outdoor unit with the suction side facing a wall and install a baffle plate on the air discharge side of the outdoor unit. They make a baffle but like I said, I haven't found one yet. Guess you could just make one...


SmokChsr
Who let the magic smoke out?
Premium
join:2006-03-17
Saint Augustine, FL
reply to Sly
said by Sly:

OIC... head pressure control will not work considering you have only one fan motor. You could put cardboard over part of the outdoor coil to restrict (but not completely block) airflow.

I don't know if it's easily available for standard home units, but several of the commercial wall hung units I work with which have to cool year round that have a head pressure switch on the condenser line that turns on the single condenser fan only once the head pressure is above a certain point. In cool temps it's not uncommon to hear the condenser fan just come on for a few seconds and cut right back off.


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
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reply to Sly
So who should I contact to get this "optional wind baffle" and is it a matter of just adding the baffle or do you also have to adjust the low temp somehow?
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Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:2
Reviews:
·Callcentric
Ok I think I found it... It looks like you can cut a jumper and it will allow the unit to operate at a lower ambient temperature. If you install the baffle it will go even further. Do you know exactly what outdoor model you have?

I found this PDF that has instructions for cutting the jumper. »www.daikinac.com/content/assets/ ··· nual.pdf
Page 8 says
Cutting jumper 3 (J3) on the circuit board will expand the operation range down to 5°F (–15°C). However it will stop if the
outdoor temperature drops below –4°F (–20°C) and start back up once the temperature rises again.
1) Remove the 3 screws on the side and remove the top plate of the outdoor unit.
2) Cut the jumper (J3) of the PCB inside.
I think I found the baffle at Johnstonesupply.com: »www.johnstonesupply.com/storefro ··· =X72-145

I'm not 100% sure this is the correct baffle and so that's why I need the outdoor model number.


Jack_in_VA
Premium
join:2007-11-26
North, VA
kudos:1
It was "0" here this morning and my unit was humming right along. Not putting out much heat but running.


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
kudos:3
reply to Sly
Thanks I'll see if I can get the model number of the outside part tonight (I thought that split mini's were sold as a pair so didn't think the outside would have such info, but I'll look)

BTW again today I woke up to my room being 78F and the server fans revving up (not constant but intermittently the servers would rev up then down)

BTW I'm taking that temp from this clock I have by my bed.

the weather station said it was 31F outside.
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pende_tim
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join:2004-01-04
Andover, NJ
kudos:1
Reviews:
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Once again.... is there no way you could blow some of that excess heat into the rest of the house and reduce the heating cost for them?

Someone is paying twice here: first power to run the computers in your room then again for the power AC to remove this heat.
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DarkLogix
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Baytown, TX
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Well then in summer I'd need to undo it.

Sure its "Possible" but would cost alot to do in a way that would keep my room cool.

basically not gonna happen.

The central Unit does have the fan set to on currently to keep air circulating some when nether heat or cold is active (it runs slower than when cooling/heating)

So I guess technically I could have an exhaust fan pull air out and send it to the central intake, but the logistics of doing that would make it costly.

I formerly had a "portable" unit that was ducted to push heat into the attic, but that thing was loud and didn't cool very well.

there just isn't a way to do it logistically that would be effective.

And ya I know its paying 3 times, because then there's also the cost of heating the house.

The air intake for the central unit is at floor level and under the furnace with very little clearance between the furnace and the wall around it, so feeding a duct to it would be difficult and be very small.
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pende_tim
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join:2004-01-04
Andover, NJ
kudos:1
Reviews:
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Could you put a fan at the supply vent in your room and "backfeed" the house through that? Or put a fan on the supply duct in your room and pull air from the house through the ducting system into your room? I assume there is a return path some where from your room to the central HVAC system so the air drawn into the room could escape.
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DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
kudos:3
AFAIK the only return path is at the base of the door, when standing at my door I can feel air rushing out.

All the vents in the house are home run to the plenum on top of the furnace, though I doubt a fan would compete very well with the furnace fan.
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HarryH3
Premium
join:2005-02-21
kudos:3
Perhaps a jump duct and a fan could be used to route the extra heat into the hall, the next room, etc.


pende_tim
Premium
join:2004-01-04
Andover, NJ
kudos:1
Yup. Suggested that a few days ago.


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
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reply to HarryH3
said by HarryH3:

Perhaps a jump duct and a fan could be used to route the extra heat into the hall, the next room, etc.

Not logistically do able.
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HarryH3
Premium
join:2005-02-21
kudos:3
said by DarkLogix:

said by HarryH3:

Perhaps a jump duct and a fan could be used to route the extra heat into the hall, the next room, etc.

Not logistically do able.

So you can dump heat from a portable A/C into the attic, but not back into the house?


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
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no


DarkLogix
Texan and Proud
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join:2008-10-23
Baytown, TX
kudos:3
Ok the model of the outside unit is
RXN12JEVJU


Sly
Premium
join:2004-02-20
Chuckey, TN
kudos:2
Reviews:
·Callcentric

1 edit
I've looked at the Engineering Data manual and the installation manual for that model and neither mentions a jumper for low ambient conditions.

»www.google.com/url?sa=t&rct=j&q= ··· 64,d.eW0
»www.google.com/url?sa=t&rct=j&q= ··· 64,d.eW0

After doing some more reading, models that have that jumper will operate in low ambient conditions because they have a built in head pressure control similar to what I posted above. When you cut that jumper, the inside fan defaults to high speed to warm up the evaporator as much as possible. Then the outside unit will pulse on and off as needed to keep the pressures high so that the compressor doesn't freeze up.

At this point I don't know if there's anything you can do, short of bypassing the outdoor temperature sensor and blocking the airflow. I'm not sure that I would recommend either. It may still be possible to install your own head pressure control if you don't mind doing some minor rewiring. I know I said earlier that you couldn't use one but after familiarizing myself with your system, I think you may be able to. The head pressure control has a thermocouple that monitors the outside coil temperature. As the temperature drops, it slows down the outside fan until the temperatures come back up. Then it raises it as needed so that the compressor doesn't overheat.

What's involved in hooking one up is basically attaching a thermocouple to the outside coil, hooking the head pressure control up to your low voltage wiring so that it knows when you are in heating vs air conditioning, and then relocating the wires that go to your outside fan to the head pressure control so that it can vary the fan speed. If you do this, then it would probably be safe to bypass the outdoor ambient temperature sensor so that it will operate below 40 degrees. The head pressure control will protect the compressor and so you won't need that sensor.

If you are willing to investigate, I would suggest just pulling the cover off the system to see if it has those jumpers. If it has jumper 3 in the same location as the above mentioned drawing, then if you are brave you might try cutting it to see if it works in low ambient mode. Like I said, your model may not have this feature but it is possible that it does and they just left it out of the manual. I can't say that this is a risk free thing to do. It's possible that it may have that jumper but it may do something else. But I would be willing to bet that if it does have the jumper and you do cut it (with the power off), and it doesn't work, you could always solder it back together.

You might also try calling a dealer to see if there is anything they can suggest. A low ambient baffle is just one of the things that will help. However none of it will matter unless you can bypass that outdoor temperature sensor that cuts the system off at 40...