A.D. Const

I have a minisplit for a Computer room If the occupant sets temp to 72 degrees the unit seems to work fine. However, if he sets to 70 degrees condenser fan line freezes ups units shuts down. Any sugestions

NickTech

whats a condenser fan line?

flashheatingand

leave the stat at 72. Ok, that was obvious. Seriously, freezing line-sets are due to either lack of air flow, or low refrigerant. First thing I would do is make sure the filter and indoor coil are clean.

I know I was joking about the 72 degree setting, but a/c isn't designed to bring down the temp in the 70 degree range. 72 is pushing it. If the room stays at 72 degrees, and the filters & coil are clean, I wouldn't stress it.

A.D. Const

My mistake, wrong choice of words. Thanks for pointing that out.

A.D. Const

Thanks that makes sense, I do appreciate your input on this.

beenthere

Probably slightly under charged. Got more then one computer/electronics room at 64°F, and no problem with them freezing up.

flashheatingand

They can bring a room down to 64 without a problem? Is the system oversized? Or is that a testiment to their capacity. Why would someone want the room to be that cool? When it kept the room at 62 was it summer? or spring?

beenthere

64°F 24/7/365

Since the servers don't have the A/C discharge air blown directly into them. The rooms are kept cooler.

Units are not oversized. They are sized to maintain that temp under full load of both the equipment, and outdoor temp.

Common for dedicated computer/electronic rooms.

Some cable equipment rooms are kept warmer.

Generally use 2 units(unless its a real small room).

Both sized to handle 75% of the load. Or each able to maintain the max allowable operating temp of the equiment, if one breaks down.


What is considered oversized in one area, can be undersized in another.

Phoenix arizona, from what I hear, is sized for a 30° difference between outdoor and indoor temp.

A.D. Const

Very helpful post thanks to both of you. This paticular comp room is very small 8 x 16, Thanks to your post I know wher to start. Thanks

A.D. Const

The same hold true for us, we maintain the Comp rms at 67 24/7, as per computer geek (sorry: Electronic Systems Analist). That's what is required. Not a big problem, but when it gets real hot outside it freezes. Ones again thanks everyone for your input.

beenthere

You could have moisture in teh system.
That is being released from the sieve/drier when it gets real hot outside. And it restrictes the TXV.

A.D. Const

Thats an option we had not considered, thanks. I have not personally seen this unit I will go to check it out. I am not very familiar with Mini-splits in general but It was my understanding that Mitsubitchi (and hence I tought all mini-split) had an electronic Refrigerant valve. Is this the case on a Fujitsu? or is it a standard TXV Valve?

beenthere

Not sure. It should be electronic.I use Sanyo. But, weather its electronic or not. Moisture has the same effect.

BigReds

I'm not familiar with mini-split, but with a/c condenser line freezing means, low gas, which also means your tx valve would need to let in more liquid. Check your superheat, i believe it should be in the range of 8-12.

beenthere

Don't forget. Mini splits have the TXV inside the outdoor unit.Although low charge will cause a unit to freeze up.Its not the only cause.And generally, a low charge won't cause it to freeze up when its hot outside, but work ok when its cool outside..

BigReds

That's whats weird, Is he sure its the condenser side and not the evaporator side? Because it would make sense that, if its the evaporator, than that would mean too much liquid is being let in through txv because its demanding more cooling. Where as on cool outside days, less demand, so less liquid txv is letting by.

beenthere

An over feeding TXV won't cause a freeze up.Provided the indoor fan is running.The small line outside the condenser is not a liquid line. It is part of the evap/distributor system.

BigReds

I've seen evaporator coils freeze up due to txv flooding the coil with too much liquid. Fan could not keep up with it. Which almost resulted in damage to compressor. The small line out side to the condenser is the discharge line which contains vapor. But lack of gas and exposed to outside air causes the vapor to turn to liquid too soon, which can then freeze up by fan. <- just answered my own question regarding if it is indeed the condenser side or evap side thats freezing up.

beenthere

Since the OP's question is on mini splits. Don't compare them with conventional systems. Convention systems, the small line is a liquid line, not a vapor line.In order for an over feeding TXV to cause a coil to freeze. More then just the TXV over feeding must occur.A 3 to 5 ton capacity TXV on a 3 ton system, set to feed 5 tons worth of refrigerant won't freeze the coil.It will flood the compressor.I've been on calls, where removing charge has stopped a coil from freezing. But, they weren't freezing only because of the over charge. They had a lot of other problems. Blower air flow, dirty indoor coils.Piston system with a 25 foot vertical drop to the indoor coil.If you go back and recheck those that you saw freeze. You can find atleast one other reason that each of them was it to freezing.The liquid line on a mini split is a distributor line.

A.D. Const

I found this last thread very interesting, especially the part where you said: "system with a 25 foot vertical drop to the indoor coil". That may be my case I am coming down from roof condenser in 4 story building to second floor comp. room MS. I am defenitely over 25 ft drop. How would the drop affects the performance. I know fan is good and filters are clean. However, what you are explaining would explain why I have moisture by drywall close to where the liquid (or if I understand correctly the discharge line of TXV.) This would make much sense. Thank you all for you helpful posts This would also mean that small line should be insulated, is not. Bad install I note