Long Lineset Instructions
Page 35
maximum allowable pressure drop The amount of
pressure drop a liquid line can experience before flash gas
will begin to form. This number can be calculated if the
amount of sub-cooling leaving the condenser is known by
subtracting the liquid temperature from the saturated liquid
temperature then converting the results into a pressure on
the HCFC-22 saturation chart. The difference in pressure
between saturated liquid temperature and the liquid
temperature is equal to the maximum allowable pressure
drop.
If the outdoor unit is charged to operate with 10F
subcooling at 115F saturated liquid temperature, the
maximum allowable pressure drop will be 30 psi.
metering (metering device) Any device which regulates
the flow of liquid refrigerant into an evaporator.
migrate (migration) The tendency of refrigerant gas to
slowly travel to the coldest part of the piping system during
the off-cycle and condense and collect as liquid.
miscibility The ability of two or more substances to mix,
and form a single homogeneous phase.
multiple evaporators A single condenser operating with
several evaporators at the same time.
non-recycling pump-down control See Pump Down
Control.
oil trap A small U bend typically located in the suction line
where it exits the indoor coil. Short radius elbows should be
used on oil traps to keep the oil volume as small as possible.
outdoor coil The name given to the coil in the outdoor unit
in heat pump systems.
pressure drop (pressure loss) The loss of refrigerant
pressure experienced in copper pipe, usually expressed in
terms of pounds (psi) per 100 feet.
pump-down control A field installed kit consisting of a
solenoid valve located in the liquid line before the
expansion valve. At the end of a cooling cycle, the controls
close the valve. The compressor continues to run until all
refrigerant is returned into the condenser where it is stored
as a liquid. The valve remains closed until the next cooling
demand.
RFC (refrigerant flow control device) OEM' trademark
protected name for various types of refrigerant metering
devices with fixed orifice size -
RFC: Liquid line serves as the expansion device. It has a
precisely sized inside diameter and length which matches
the capacity of the condensing unit and evaporator.
RFCII: Fixed orifice for air conditioners located at
evaporator.
RFCIII: Floating bullet type orifice for heat pump coils which
front seats for cooling and back seats for heating
RFCIV: Fixed bullet orifice for air conditioners.
riser The name of any length of refrigerant pipe which
transports refrigerant vertically upward.
run-around hot gas bypass A type of hot gas bypass
system that diverts hot discharge gas and liquid directly into
the suction line inside the condensing unit. Although this
type of system requires no piping external to the unit, it is
less desirable than feeding into a side tap on the distributor
on the evaporator coil.
saturation temperature The temperature at which a gas
begins to turn into liquid.
sight glass A glass window type device placed in a liquid
line and used for visual inspection of the liquid. It can also
be used to determine the point at which all gas bubbles are
removed from the liquid line. A sight glass is not a good
indicator of subcooling and cannot be used to determine
charge.
sil-phos Brazing material composed of silver,
phosphorous, and copper and used for brazing joints of
copper pipe.
slug A column of liquid refrigerant returned to the
compressor in the suction line. A slug which enters the
compressor can cause permanent compressor damage
due to non-compressibility of liquids.
solenoid valve An electromechanical valve located in the
refrigerant lines and used to shut-off refrigerant flow.
split-coil
A single evaporator or condenser coil which is
plumbed so that a single coil can serve two or more
independent refrigeration circuits.
subcooling Cooling of refrigerant liquid below its saturated
temperature while holding it at saturated pressure.
suction riser See Riser.
superheat Heating of refrigerant gas above its saturated
temperature while holding it at saturated pressure.
thermometer well A device located in the liquid line of most
OEM equipment which allows a thermometer to be inserted
into the liquid line. The well is used for accurately
measuring the temperature of the liquid line for charging
purposes.
thermostatic expansion valve (TXV) An extremely
precise type of expansion device which regulates
refrigerant flow into the evaporator based on the amount of
superheat at the TXV bulb location. An expansion valve is
desirable in long line set applications because it can
maintain control of superheat in extremes of operating
conditions.
trap See Oil Trap.
two stage Condensing (or heat pump) outdoor units
equipped with a two stage compressor. Generally, the
compressor operates at 60% capacity on low stage and
100% capacity on high stage.
TXV See Thermostatic Expansion Valve.
unload (unloading) See Capacity Reduction.
Vapor line Term used with heat pumps to describe the
discharge hot gas line in heating mode and the suction line
in cooling mode. In either mode the line carries refrigerant
in a vapor form.
variable capacity See Capacity Reduction.
velocity A measure of the speed at which refrigerant
travels through a pipe, usually expressed in feet per minute.
wrought copper Hammered refrigeration grade copper
used in refrigerant fittings.