Service Manual
SERVICING
35
A superheat charge chart is available for other operating condi-
tions. Use it to provide the correct superheat at the conditions
the unit is being charged at.
After superheat is adjusted it is recommended to check unit
sub-cooling at the condenser coil liquid line out. In most oper-
ating conditions 12
+ 4
0
F of sub-cooling is adequate.
An inaccurately charged system will cause future problems.
1. Using a quality set of charging scales, weigh the proper
amount of refrigerant for the system. Allow liquid refrigerant
only to enter the high side.
2. After the system will take all it will take, close the valve on
the high side of the charging manifold.
3. Start the system and charge the balance of the refrigerant
through the low side.
NOTE: R410A should be drawn out of the storage con-
tainer or drum in liquid form due to its fractionation proper-
ties, but should be "Flashed" to its gas state before enter-
ing the system. There are commercially available restric-
tion devices that fit into the system charging hose set to
accomplish this. DO NOT charge liquid R410A into the
compressor.
4. With the system still running, close the valve on the charg-
ing cylinder. At this time, you may still have some liquid
refrigerant in the charging cylinder hose and will definitely
have liquid in the liquid hose. Slowly 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 refrig-
erant does not enter the compressor.
Final Charge Adjustment
The outdoor temperature must be 60°F or higher. Set the room
thermostat to COOL, fan switch to AUTO, and set the tem-
perature control well below room temperature.
After system has stabilized per start-up instructions, compare
the operating pressures and outdoor unit amp draw to the num-
bers listed in the technical manual. If pressures and amp draw
are too low, add charge. If pressures and amp draw are too
high, remove charge. Check subcooling and superheat as de-
tailed in the following section.
5. With the system still running, remove hose and reinstall
both access fitting caps.
6. Check system for leaks.
Due to their design, Scroll compressors are inherently more
tolerant of liquid refrigerant.
NOTE: Even though the compressor section of a Scroll com-
pressor is more tolerant of liquid refrigerant, continued flood-
back or flooded start conditions may wash oil from the bearing
surfaces causing premature bearing failure. S-104 CHECK-
ING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll com-
pressors, reducing the ability of the compressor to pump re-
frigerant vapor.
The condition of the valves or scroll flanks is checked in the
following manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run a Cooling Performance Test.
If the test shows-
⇒
Below normal high side pressure.
⇒ Above normal low side pressure.
⇒
Low temperature difference across coil.
⇒ Low amp draw at compressor.
-and the charge is correct. The compressor is faulty - replace
the compressor.
S-104 CHECKING COMPRESSOR
EFFICIENCY
The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll com-
pressors, reducing the ability of the compressor to pump re-
frigerant vapor.
During the "OFF" cycle, the high side pressure bleeds to the
low side through the fixed orifice restriction device. Check
equalization time as follows:
1. Attach a gauge manifold to the suction and liquid line ac-
cess fittings.
2. Start the system and allow the pressures to stabilize.
3. Stop the system and check the time it takes for the high
and low pressure gauge readings to equalize.
If it takes more than seven (7) minutes to equalize, the restrictor
device is inoperative. Replace, install a liquid line drier, evacu-
ate and recharge.
S-108 SUPERHEAT
CHECKING SUPERHEAT
Refrigerant gas is considered superheated whenever its tem-
perature is higher than the saturation temperature correspond-
ing to its pressure. The degree of superheat equals the de-
grees of temperature increase above the saturation tempera-
ture at existing pressure. See Temperature - Pressure Chart.