Trane TR-SCS Series Installation, Operation And Maintenance Manual page 20

Installation
charge will be performed by introducing liquid refrigerant
(R407C or R410A) to the discharge side of the compressor
or an available liquid line port with the A/C unit turned Off.
1. Bleed air from hoses and break the vacuum by
supplying liquid refrigerant (R407C or R410A) to the
discharge port near the compressor until the pressure
is equalized. This holding charge allows the low
pressure switch to hold enabling the compressor to
operate throughout the process of charging the
system.
Fine Tuning the System Charge
Once the initial charge is completed, additional refrigerant
will need to be added with the unit running until the
superheat temperature can be maintained between 12–
15°F.
2. Disconnect the refrigerant cylinder from the discharge
side of the compressor and connect it to the suction
side.
3. Start the A/C system and use the system controller to
lower the room temperature setpoint 3–5°F below
actual room temperature thus ensuring cooling
remains on as the unit is charged.
NOTICE
Compressor Damage!
POE oil is used in systems with R407C or R410A
refrigerant. POE oil quickly absorbs moisture when
exposed to air. High POE oil moisture levels react with
refrigerant to form acid which results in system
contamination. Keep the entire system sealed as much
as possible and minimize exposure of the POE oil to
outside air.
When fine tuning the charge during low ambient
conditions it will be necessary to restrict the airflow across
the condenser coil to raise the pressure. The fan closest to
the header must be running. Refrigerant R407C operates
at a lower pressure than R410A. When fine tuning the
charge, ensure the pressures are correct for the type of
refrigerant used.
0ºF Fan Cycling and -20ºF Variable Speed
Control
The following instructions are for charging systems
provided with condenser fan cycling or variable fan speed
control during low ambient conditions using R407C or
R410A refrigerant.
1. Block off the intake air to the condenser with cardboard
until a constant discharge pressure can be obtained.
This will lower the possibility of overcharging (for units
with fan cycling only).
a. R407C Refrigerant- Allow the discharge pressure to
rise to 325–350 psig and hold it constant.
b. R410A Refrigerant- Allow the discharge pressure to
rise to 445–480 psig and hold it constant.
20
NOTICE
Compressor Damage!
Failure to follow instructions below could result in
compressor failure and/or reduced compressor life.
To prevent compressor liquid slugging, only add liquid
in the suction line when the compressor is running. Use
extreme caution to meter liquid refrigerant into the
suction line slowly. If liquid is added too rapidly,
compressor oil dilution and oil pumpout could occur.
2. Slowly meter liquid refrigerant through the suction
side while watching the pressure gauge and
monitoring superheat and sub-cooling temperatures.
3. Take a superheat temperature reading near the feeler
bulb from the thermostatic expansion valve with the
temperature measuring device being well insulated.
The ideal superheat temperature is 10–15°F. Maximum
allowable superheat temperature is 20°F.
4. While monitoring the pressure, take a sub-cooling
temperature reading on the output side of the
condenser. The sub-cooling temperature should be
10–20°F.
5. If necessary, (slowly) add liquid refrigerant to the
suction side to achieve the sub-cooling temperature.
6. If the unit has hot gas reheat (optional), the previous
steps are still followed except the hot gas reheat valve
must be open to allow refrigerant to flow into the
reheat coil to obtain the proper amount of refrigerant
charge. This can be done by using the system
controller to enable a call for dehumidification (lower
the humidity setpoint). This process may need to be
repeated several times. After cycling the system
through the hot gas reheat cycle, recheck the system
charge with the system only in the Cooling mode.
Important: Remove the blockage to the air intake of the
condenser. Fill out the applicable sections
of Warranty Registration and Start-Up
Checklist.
-30 °F Flooded Head Pressure Control
Note: For units using flooded head pressure control, a
receiver is used to store the refrigerant during the
time the condenser is not utilizing the extra
refrigerant charge.
Note: It is important not to exceed 80% of the total
condenser and receiver volume to allow room for
expansion.
Perform the initial system charge. Energize all solenoids,
hot gas bypass, hot gas reheat, etc. The condenser fan
nearest the condenser header should be operating
continuously. If not change the fan control setting to force
continuous operation. All other fans, if additional fans
exist, should be off during this time.
SS-SVX006C-EN