Trane Voyager Commercial, Installation, Operation And Maintenance Manual

Page: 105 / 156

RT-SVX34R-EN 105
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
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1. 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. 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.
N No otte e:: 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 , p. 68 to Table 46, p. 74 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 than the modulating can provide, the second
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