13
REFRIGERANT BLENDS — TEMPERATURE GLIDE
The majority of HFC refrigerants in use today are referred to as refrigerant “blends” (composed of two or more different refrigerants).
As such, each component within this “blend” evaporates (or condenses) at different temperatures. The temperature range within which
each of these different refrigerants completely changes state from a liquid to a gas (or vice versa) is referred to as “temperature glide”.
Essentially this means that the traditional way we measure superheat and liquid sub-cooling must be adjusted to account for this
temperature “glide”. Depending upon which one of these refrigerant is used in the system the temperature glide could range from as
low as 6 to perhaps as high as 12 degrees. Technically R-404A is also a blend but since it’s temperature glide is only around 1 degree
it is typically treated as an azeotrope (a refrigerant whose components boil and evaporate at the same temperature).
When measuring superheat at the evaporator outlet of a system utilzing any of these high glide rfrigerants you must always refer to the
refrigerants’ “Dew Point” which is the point at which the last droplet of liquid refrigerant has vaporized. These values are all listed for
easy reference on all current temperature pressure charts, mechanical and electronic service gauge manifolds and apps commonly
used by todays field service technicians. If in doubt about the values you’ve measured always refer to published data supplied by the
various refrigerant manufacturers to confirm your field measurements. Regardless of which type of refrigerant is used in the system
the service technicians goal is still the same - to maximize the evaporator performance while ensuring both adequate compressor motor
cooling and the prevention of liquid floodback
.
The diagram on the right graphically illustrates the relationship
or “glide” of two different components making up a single refrig-
erant blend as they pass through the evaporator coil. The
number on the left of the / mark represents the percentage of
refrigerant “A” and the number to the right of the / mark repre-
sents the percentage of refrigerant “B” which is present at each
location (1, 2 & 3) in the evaporator coil.
Note that the mixture is only equal (50/50) at the inlet
(100% liquid) and at the outlet (100% vapor) of the evapo-
rator coil.
FIELD WIRING — ELECTRICAL REQUIREMENTS
The electrical characteristics of each unit are clearly marked on the unit rating label located on the front facing, left hand end cover of
the unit (as viewed facing the fans). This label lists the operating voltage, phase and amp draw of the fan motors and defrost heaters
(when equipped). It also lists the
MINIMUM CIRCUIT AMPACITY
(
MCA
) and
MAXIMUM OVER CURRENT PROTECTION DEVICE
(
MOPD
) which should be used in order to determine the minimum wire gauge size required to supply power to the unit and the largest
circuit breaker / fuse size it should be fed from. These values apply only to the main power supply to the unit - there may be separate,
field control circuit wiring required which can be ran in smaller gauge wiring, but must still be suitable for the applied voltage.
All field wiring must be ran using copper conductors only and in total compliance with the National Electrical Code (NEC) as well as
any local or state codes. There are multiple knockouts supplied on the electrical end of the unit (opposite the refrigerant connection
end) to accommodate field installed wiring / conduit connections. Field wiring must be landed on the factory supplied terminal block
located inside the electrical end panel. Refer to the unit wiring diagram located on the inside of the electrical end cover panel for the
specific terminals to connect to. When making the field wiring connections it is always advisable to double check the factory wiring
connections to be sure that none have loosened in shipment or are otherwise dislodged from their terminals. The unit must also be
properly grounded which may require that a dedicated ground wire be ran to the unit (depending upon local code requirements and
the type of conduit utilized in the installation).
The fan motors for all air defrost units are factory
wired to the terminal block. On electric defrost units
all fan motors, defrost heaters, heater safety and fan
delay / defrost termination controls are factory wired.
If not provided as a factory mounted option it is the
installing contractors responsibility to install and wire
a room thermostat, liquid line solenoid valve and de-
frost timer (when required). The typical wiring dia-
grams supplied on the following pages will assist with
the field wiring of these controls - as well as wiring for
multiple units on a single system when required.
MOTORS
K
J
N P
Fig. 5
Heater Safety
Field Power Wiring
Defrost Termination
Fan Delay Control
Factory Mounted
Junction Box /
Terminal Block
FACTORY WIRING
