It would seem that your setup is fine...your problem seems to lie with A/C technicians that work like doctors. They aren't sure what the problem is so the take a guess and fix one thing at a time until something works without really knowing what's causing the problem...being out there for the 3rd time when you haven't had issues in 5 years.

I've worked in server rooms for quite a few years, but I can't say that I've ever inquired about how the A/C system works. But I do know when working in the server room, it alway seemed windy. The main issue isn't really cooling the air, it's the transfer of air. Just as inside the computers themselves...they don't run cool air over the heat sinks, they just run plain air to move the hot air away. Ambient air will always be cooler than what the systems are generating. So you mainly just need a flow going to push the hot air out. Adding in cold air is just a bonus for extra cooling.

Case in point, I was working in a server room once when the fan to the A/C unit broke. We went from 68 degree to about 100 degrees in less than an hour. By the time we got a bunch of huge fans in the area to circulate the air, the temperature dropped to low 90s, high 80s...and that was without cooling and our crappy quick fix circulation.

Guess the point here is...seems like you have a working layout solution. Just keep the air circulation going.

Here's my take on the situation: There's gotta be a Pelicanite nearby in the HVAC biz that wouldn't mind taking a look and maybe trying a fix. It could be worth a nice swap...labor vs. Porsche parts! ;)

Wayne, having 10yrs experience working on computer room a/c units (Phone company:)) I can tell you this. Cleanliness needs to be paramount... also redundancy needs to be built in to your system... What I mean is, you need a lead and a lag unit.... These units will change lead/lag weekly to insure equal run time on the compressors... also, The lead unit only cools, and the lag unit needs to have it's fan running continuously... what this does, is continually circulate air, but also prevents the lead unit from running after cooling has stopped, and redepositing the moisture that it has collected back into the air... If, you are utilizing cool dry air as return air, you run the risk of dropping your humidity too low, to the point that static electricity becomes an issue, and electronics can be knocked out due to these situations... also, if your main unit goes out, you have a back up... as far as the freezing up situation, it is possible that the evaporator is freezing up due to the cold air for one simple reason, usually you have a 10-20 degree split between supply air and discharge air... that being said, if your supply air is 60 degrees and you have a 20 degree split, that means your discharge air would be approximately 40 degrees, which would mean that you coil temperature has dropped below freezing... you may remedy the situation by overcharging it, but run the risk of damaging the valves in the compressor... If I were your a/c guy I would recommend only cooling the air in the room that needs to be conditioned... I would not import or export it... Computer rooms are considered critical for a reason and are generally taken better care of / more expense applied to than personnel occupied spaces....

All he needs to do is send me a plane ticket and I would be more than willing to look at it for him....:D

I'd need a plane ticket, a nice hotel room and a big juicy steak..

JR

Wayne,

What is the make and model of your server room unit? Thanks.

He might get you some fuel from the refinery across the street.

I guess El Segundo is a bit different than 10 years ago...

The A/C guy is probably thinking of the balance of make up air, nothing too much more serious than that. A closed loop system keeps the intake and supply relatively balanced introducing a small amount of outside air, which is user adjustable on window units. Larger units are fairly well engineered with respect to exchange rates and make up air.

Wayne, your exhaust fan can't be more CFM than the A/C unit is pulling in or you will be pulling in dirty, unconditioned air. The A/C guy doesn't know what you have exactly, so he is playing it safe. You want a lightly positive system, certainly not negative.

Something has changed. If your tech has been servicing the unit for a while he should be able to pick that up.
+ 3 or 4 to airflow then charge. It is possible that the TX valve if equipped has lost pressure in its element simulating a full closed valve. Eventually this will cause a full freeze on the coil, but it takes a long time to do it. If charge is good and airflow is unchanged, look to the metering device. They can wear and develop glitches and allow full flood and coil starvation.
Has the system been topped up lately? Correct Refrigerant? Oil compatibility?