Service Manual

SERVICING
33
3. If the vacuum pump is working properly, close the valve to the
vacuum thermocouple gauge and open the high and low side
valves to the high vacuum manifold set . With the valve on t he
charging cylinder closed, open the manifold valve to the cyl-
inder.
4. Evacuate the syst em to at least 29 inches gauge before open-
ing valve to thermocouple vacuum gauge.
5. Cont inue to evacuate to a minimum of 250 microns. Close
valve to vacuum pump and watch rate of rise. If vacuum
does not rise above 1500 microns in t hree to five minutes,
system can be considered properly evacuat ed.
6. If thermocouple vacuum gauge continues to rise and levels
off at about 5000 microns, moist ure and non-condensables
are st ill present. If gauge continues to rise a leak is present.
Repair and re-evacuate.
7. Close valve t o thermocouple vacuum gauge and vacuum
pump. Shut off pump and prepare to charge.
S-103 CHARGING
WARNINGWARNING
CAUTION
Charge the syst em with the exact amount of refrigerant .
Refer to the specification sect ion or check the unit nameplates
for the correct refrigerant charge.
Aft er complet ing airflow measurement s and adjustments, the
unit’s refrigerant charge must be checked. The unit comes fac-
tory charged, but this charge is based on 400 CFM per ton at
minimum ESP per AHRI t est condit ions (generally between .15 -
.25 ESP). When air quantit y or ESP is different than above, charge
must be adjust ed t o the proper amount .
All package units are charged to the superheat method at the
compressor suct ion line (these are fixed orifice devices).
For charging in the warmer months, 10
0
F superheat at the com-
pressor is required at condit ions: 95
0
F outdoor ambient (dry bulb
temperature), 80
0
F dry bulb / 67
0
F wet bulb indoor ambient,
approximat ely 50% humidity. This superheat varies when condi-
tions vary from the conditions described.
A superheat charge chart is available for other operat ing condi-
tions. Use it to provide the correct superheat at t he conditions
the unit is being charged at.
Aft er superheat is adjusted it is recommended to check unit sub-
cooling at the condenser coil liquid line out. In most operating
conditions 12 + 4
0
F of sub-cooling is adequat e.
An inaccurat ely charged syst em will cause fut ure problems.
1. Using a quality set of charging scales, weigh the proper
amount of refrigerant for the syst em. Allow liquid refriger-
ant only to enter the high side.
2. Aft er the syst em will take all it will t ake, close t he valve on
the high side of the charging manifold.
3. St art the syst em and charge the balance of the refrigerant
through the low side.
NOTE: R410A should be drawn out of the st orage container
or drum in liquid form due to its fractionat ion properties,
but should be "Flashed" to its gas st ate before entering the
system. There are commercially available restriction devices
that fit into the syst em charging hose set to accomplish this.
DO NOT charge liquid R410A into the compressor.
4. With the system st ill running, close the valve on t he charg-
ing cylinder. At this time, you may st ill have some liquid
refrigerant in t he charging cylinder hose and will definitely
have liquid in the liquid hose. Slow ly open the high side
manifold valve and transfer the liquid refrigerant from the
liquid line hose and charging cylinder hose into the suction
service valve port . CAREFUL: Watch so that liquid refriger-
ant does not enter the compressor.
Final Charge Adjustment
The outdoor temperature must be 60°F or higher. Set the room
thermostat to COOL, fan sw itch to AUTO, and set the tempera-
ture control well below room temperature.
Aft er syst em has st abilized per st art-up inst ructions, compare
the operat ing pressures and outdoor unit amp draw to the num-
bers listed in the technical manual. If pressures and amp draw
are t oo low, add charge. If pressures and amp draw are t oo high,
remove charge. Check subcooling and superheat as detailed in
the following section.
5. With the system st ill running, remove hose and reinst all bot h
access fitt ing caps.
6. Check syst em for leaks.
Due to their design, Scroll compressors are inherent ly more t ol-
erant of liquid refrigerant.
NOTE: Even though the compressor section of a Scroll compressor is
more tolerant of liquid refrigerant , cont inued floodback or flooded
st art conditions may wash oil from the bearing surfaces causing
premature bearing failure. S-104 CHECKING COM PRESSOR EFFI-
CIENCY