Startup
RT-SVX34F-EN
85
Scroll Compressor Operational Noises
Because the scroll compressor is designed to
accommodate liquids (both oil and refrigerant) and solid
particles without causing compressor damage, there are
some characteristic sounds that differentiate it from those
typically associated with a reciprocating compressor.
These sounds (which are described below) are
characteristic, and do not affect the operation or reliability
of the compressor.
At Shutdown
When a Scroll compressor shuts down, the gas within the
scroll compressor expands and causes momentary
reverse rotation until the discharge check valve closes.
This results in a “flutter” type sound.
At Low Ambient Startup
When the compressor starts up under low ambient
conditions, the initial flow rate of the compressor is low
due to the low condensing pressure. This causes a low
differential across the thermal expansion valve that limits
its capacity. Under these conditions, it is not unusual to
hear the compressor rattle until the suction pressure
climbs and the flow rate increases.
During Normal Operation
The scroll compressor emits a higher frequency tone
(sound) than a reciprocating compressor.
Compressor Crankcase Heaters
Each compressor is equipped with a crankcase heater.
When the compressor is “Off”, the crankcase heater is
energized. When the compressor is “On”, the crankcase
heater is de-energized. The proper operation of the
crankcase heater is important to maintain an elevated
compressor oil temperature during the “Off” cycle which
reduces the potential for refrigerant to migrate into the
compressor oil.
If present during a compressor start, liquid refrigerant
could damage compressor bearings due to reduced
lubrication and eventually could cause compressor
mechanical failures.
Prior to the initial start or when power to the unit has been
“Off” for an extended period, allow the crankcase heater to
operate a minimum of 8 hours before starting the unit.
Charging by Subcooling
The unit is shipped with a complete refrigerant charge.
However, if it becomes necessary to add refrigerant, it
should be done so by adding charge to obtain an
acceptable subcooling as described below. Refer to the
maintenance section for proper refrigerant charging
practices.
The outdoor ambient temperature must be between 65°
and 105° F and the relative humidity of the air entering the
evaporator must be above 40 percent. When the
temperatures are outside of these ranges, measuring the
operating pressures can be meaningless.
With the unit operating at “Full Circuit Capacity”,
acceptable subcooling ranges between 14° F to 22° F.
Measuring Subcooling
1.
At the liquid line service valve, measure the liquid line
pressure. Using a Refrigerant R-410A pressure/
temperature chart, convert the pressure reading into
the corresponding saturated temperature.
2. Measure the actual liquid line temperature as close to
the liquid line service valve as possible. To ensure an
accurate reading, clean the line thoroughly where the
temperature sensor will be attached. After securing the
sensor to the line, insulate the sensor and line to isolate
it from the ambient air.
Note:
Glass thermometers do not have sufficient contact
area to give an accurate reading.
3. Determine the system subcooling by subtracting the
actual liquid line temperature (measured in step 2)
from the saturated liquid temperature (converted in
step 1).
Gas Heat Units
Open the main disconnect switch to shut the unit off and
to reset the RTRM.
Follow the Test Guide in
Table 31, p. 56
-
Table 36, p. 58
to
start the unit in the heating mode. Jumping the “Test”
terminals several times for two to three seconds will be
required.
When starting the unit for the first time or servicing the
heaters, it is a good practice to start the heater with the
main gas supply turned “Off”.
All heating units have either two stage or modulating heat
capabilities. The “High” heat models contain two heat
exchangers. In staged units, the heat exchangers operate
simultaneously at either the low or high fire state. In
modulating units, the modulating furnace fires first and
adjusts to the needed capacity. If more heat is required
WARNING
R-410A Refrigerant under Higher Pressure
than R-22!
The units described in this manual use R-410A
refrigerant which operates at higher pressures than R-
22 refrigerant. Use ONLY R-410A rated service
equipment or components with these units. For
specific handling concerns with R-410A, please contact
your local Trane representative.
Failure to use R-410A rated service equipment or
components could result in equipment exploding under
R-410A high pressures which could result in death,
serious injury, or equipment damage.
