Old and Grunpy wrote:
"Uncle Monster" wrote in message
...
markm75 wrote:
I'm lookin to get an AC window unit in my 9x12 office.. not sure on
the btu i would need, but i have a lot of computer equipment forcing
the ambient temp in the room from about 78 to as high as 85 at times
(at mid height in the room)..

I've had window units years ago and i remember having trouble when it
got colder.. the unit would freeze up.. do they all do this these
days.. as i'd need to run this unit in the winter time too..

I'm hoping to find one with thermostat control, so when the room
reaches a temp it shuts off too.

We have whole house ac, but this room gets hot, despite this.

Thanks for any advice..

I do a lot of commercial HVAC and refrigeration
work and when I have to run a piece of equipment
under low ambient conditions like the AC at a
restaurant which often has to run in the winter,
I install whats called a "head pressure" or "low
ambient" control. For the large AC unit that you
would find at a restaurant, it's a simple matter
of controlling the condenser fan. When the fan
is turned off by the electric controller, the head
pressure rises until reaching a preset limit then
the condenser fan comes back on. This keeps things
from freezing up and protects the compressor from
flooding with liquid freon.

Sorry Uncle that does not stop refrigerant from floading compressor
but actually does the oposit however it helps for compressor from
cutting out on low pressure switch and saving compressor from
pumping oil out of crankcase. However for the health of compressor
if unit is going to be use all year round additional items need to be
install
(depend) on system size, Crankcase heater, suction accumulator,
large Recivers also need rap around heater.


The problem with a
window unit is that there is only one motor turning
both condenser and evaporator fans. To control the
head pressure in that situation you need to modify
the plumbing and add a head pressure control that
controls the flow of freon. This type of control
throttles the head pressure by opening and closing
a valve to keep the head pressure within a certain
range. What I've written here is a bit simplistic
in explaining the process but a good refrigeration
guy could modify your window unit. Most AC techs
don't get into plumbed in controls which is what
refrigeration techs tackle all the time. Here are
some links to information that may help you grasp
the process and explain in more detail than I can
here.

http://tinyurl.com/52houb

http://tinyurl.com/4f8xr3

I hope this helps you out.

[8~{} Uncle Monster



Most of the systems I install have crankcase
heaters anyway. When I order a new unit I get
all the bells and whistles like high and low
pressure cutouts, phase/voltage protection
modules, head pressure controls, etc. Some of
the units have suction line accumulators like
the 4 ton Carrier condensing unit here at the
office. Somebody got on the roof last summer
and thought it belonged to my neighbor in the
next shop, the silly ******* left the service
valves loose and all the freon got loose and
went off to kill some helpless little ozones.
It took 13lbs of R22 to recharge it and until
I saw this huge accumulator next to the
compressor, I wondered where in the hell the
charge was going. In my previous post I said
my explanation was "simplistic". Anyway, I
posted what I thought would work for the guy
in another thread and suggested a portable AC
unit which is what I've used to cool small
computer server rooms before. The whole unit
is in the room and uses a big hose to exhaust
hot air. No low ambient problems there.

http://www.portableairshop.com/

[8~{} Uncle Monster