Service Manual

SERVICING
35
Subcooling Formula = Sat. Liquid Temp. - Liquid Line
Temp.
EXAM PLE:
a. Liquid Line Pressure = 417
b. Corresponding Temp. °F. = 120°
c. Thermometer on Liquid line = 109°F.
To obtain the amount of subcooling, subtract 109°F from 120°F.
The difference is 11° subcooling. See the specification sheet or
technical informat ion manual for t he design subcooling range
for your unit.
See R410A Pressure vs. Temperat ure chart.
S-111 FIXED ORIFICE RESTRICTION DEVICES
The fixed orifice rest riction device (flowrat or) used in conjunc-
tion wit h the indoor coil is a predetermined bore (I.D.).
It is designed to control the rate of liquid refrigerant flow int o an
evaporator coil.
The amount of refrigerant that flows through the fixed orifice
rest riction device is regulated by the pressure difference between
the high and low sides of the syst em.
In the cooling cycle when the out door air temperature rises, t he
high side condensing pressure rises. At the same t ime, the cool-
ing load on t he indoor coil increases, causing t he low side pres-
sure t o rise, but at a slow er rat e.
Since the high side pressure rises faster when t he t emperature
increases, more refrigerant flows to the evaporator, increasing
the cooling capacity of the syst em.
When the outdoor temperature falls, the reverse takes place.
The condensing pressure falls, and the cooling loads on the in-
door coil decreases, causing less refrigerant flow.
If a restriction should become evident , proceed as follows:
1. Recover refrigerant charge.
2. Remove the orifice assembly and clean or replace.
3. Replace liquid line drier, evacuat e and recharge.
CHECKING EQUALIZATION TIM E
During t he " OFF" cycle, t he high side pressure bleeds t o the low
side through the fixed orifice rest riction device. Check equaliza-
tion time as follows:
1. At t ach a gauge manifold to the suction and liquid line dill
valves
2. St art the syst em and allow the pressures t o st abilize.
3. Stop the syst em and check the t ime it takes for the high and
low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the rest riction
device is inoperat ive. Replace, install a liquid line drier, evacuat e
and recharge.
S-112 CHECKING RESTRICTED LIQUID LINE
When the system is operating, the liquid line is warm to the touch.
If the liquid line is rest ricted, a definite temperature drop will be
noticed at the point of restriction. In severe cases, frost will form
at the rest riction and extend down the line in t he direction of the
flow.
Discharge and suction pressures will be low, giving the appear-
ance of an undercharged unit. However, the unit will have nor-
mal to high subcooling.
If a restriction is located, replace the rest ricted part , replace drier,
evacuat e and recharge.
S-113 REFRIGERANT OVERCHARGE
An overcharge of refrigerant is normally indicated by an exces-
sively high head pressure.
An evaporator coil, using an expansion valve met ering device,
will basically modulate and control a flooded evaporat or and
prevent liquid refrigerant from returning to the compressor.
An evaporator coil, using a fixed orifice restrictor device
(flowrat or) metering device, could allow liquid refrigerant to re-
turn to the compressor under extreme overcharge conditions.
Also with a fixed orifice restrictor device (flowrator) metering
device, extreme cases of insufficient indoor air can cause icing of
the indoor coil and liquid refrigerant to return to the compres-
sor, but the head pressure would be lower.
There are other causes for high head pressure which may be found
in the "Service Problem Analysis Guide."
If other causes check out normal, an overcharge or a syst em con-
taining non-condensables would be indicated.
If this system is observed:
1. St art the syst em.
2. Remove and capture small quantities of refrigerant as from
the suction line access fitting until t he head pressure is re-
duced to normal.
3. Observe the syst em while running a cooling performance test.
If a short age of refrigerant is indicat ed, then the syst em con-
tains non-condensables.
S-114 NON-CONDENSABLES
If non-condensables are suspect ed, shut down the syst em and
allow the pressures to equalize. Wait at least 15 minutes. Com-
pare t he pressure to t he temperature of the coldest coil since
this is where most of the refrigerant will be. If the pressure indi-
cates a higher temperature than that of the coil t emperature,
non-condensables are present.
Non-condensables are removed from the syst em by first removing
the refrigerant charge, replacing and/ or inst alling liquid line drier,
evacuat ing and recharging.