Subcooling; Measuring Superheat; Compressor Oil; Compressor Crankcase - Trane RAUJ-C20 Installation, Operation And Maintenance Manual

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N N o o t t e e : : Interchanging "Load" side power wires at the

contactors only affects the individual fan

rotation. Ensure that the voltage phase

sequence at the main terminal block 1TB1 is

ABC as outlined in the "Electrical Phasing"

section.

Some Motors are Rotating Backward

1. Turn the field supplied disconnect switch or circuit

protector switch that provides power to the

condensing unit to the "Off" position. Lock the

disconnect switch in the open position while

working at the unit.

2. If the unit main power phase sequence is correct,

rotation of an individual motor will be backwards if

any two leads are interchanged between the unit

main power and the motor. Verify that wiring from

the unit main power to the motor is per the unit

wiring diagram. Refer to the illustration in Figure 63

for the compressor terminal/phase identification.

Compressor damage could occur if a compressor

runs backwards for a very short period of time.

Subcooling

The outdoor ambient temperature must be between

65ºF and 105ºF 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 8ºF to 16ºF.

Measuring Subcooling

N N o o t t e e : : System charging is done by using the System

Charging Chart. Do not attempt to charge the

system based on subcooling.

•

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.

•

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.

N N o o t t e e : : Glass thermometers do not have sufficient

contact area to give an accurate reading.

•

Determine the system subcooling by subtracting

the actual liquid line temperature from the

saturated liquid temperature.

SS-SVX11K-EN

Measuring Superheat

•

Measure the suction pressure at the outlet of the

evaporator as close to the expansion valve bulb

location as possible.

•

Measured the suction line temperature as close to

the expansion valve bulb, as possible.

•

Using a Refrigerant/Temperature chart, convert the

pressure reading to a corresponding saturated

vapor temperature.

N N o o t t e e : : On many Trane fan/coil units, an access valve

is provided close to the expansion valve bulb

location. This valve must be added on

climate changers and other evaporators.

•

Subtract the saturated vapor temperature, from the

actual suction line temperature. The difference

between the two temperatures is known as

"superheat".

Compressor Oil

N N O O T T I I C C E E

C C o o m m p p r r e e s s s s o o r r D D a a m m a a g g e e ! !

P P O O E E o o i i l l i i s s h h y y g g r r o o s s c c o o p p i i c c – – i i t t a a b b s s o o r r b b s s w w a a t t e e r r d d i i r r e e c c t t l l y y

f f r r o o m m t t h h e e a a i i r r . . T T h h i i s s w w a a t t e e r r i i s s n n e e a a r r l l y y i i m m p p o o s s s s i i b b l l e e t t o o

r r e e m m o o v v e e f f r r o o m m t t h h e e c c o o m m p p r r e e s s s s o o r r o o i i l l a a n n d d c c a a n n r r e e s s u u l l t t i i n n

c c o o m m p p r r e e s s s s o o r r f f a a i i l l u u r r e e s s . .

T T o o p p r r e e v v e e n n t t P P O O E E o o i i l l f f r r o o m m a a b b s s o o r r b b i i n n g g w w a a t t e e r r , , t t h h e e

s s y y s s t t e e m m s s h h o o u u l l d d n n o o t t r r e e m m a a i i n n o o p p e e n n f f o o r r l l o o n n g g e e r r t t h h a a n n

n n e e c c e e s s s s a a r r y y . . W W h h e e n n o o p p e e n n , , d d r r y y n n i i t t r r o o g g e e n n s s h h o o u u l l d d f f l l o o w w

t t h h r r o o u u g g h h t t h h e e p p i i p p i i n n g g . . O O n n l l y y n n e e w w o o i i l l c c o o n n t t a a i i n n e e r r s s s s h h o o u u l l d d

b b e e u u s s e e d d f f o o r r s s e e r r v v i i c c e e a a n n d d m m a a i i n n t t e e n n a a n n c c e e . . A A l l w w a a y y s s u u s s e e

t t h h e e s s m m a a l l l l e e s s t t c c o o n n t t a a i i n n e e r r s s i i z z e e r r e e q q u u i i r r e e d d f f o o r r t t h h e e j j o o b b

r r e e q q u u i i r r e e m m e e n n t t s s . . A A l l w w a a y y s s l l e e a a v v e e t t h h e e o o i i l l c c o o n n t t a a i i n n e e r r

t t i i g g h h t t l l y y s s e e a a l l e e d d u u n n t t i i l l t t i i m m e e o o f f u u s s e e . . D D o o n n o o t t r r e e u u s s e e o o i i l l

t t h h a a t t h h a a s s b b e e e e n n o o p p e e n n e e d d . .

RAUJ unit and replacement compressors ship fully

charged with POE oil from the factory. The scroll

compressor uses POE oil (OIL00079 for a quart

container or OIL00080 for a gallon container) without

substitution. The appropriate oil charge for a 7.5 Ton

scroll compressor is 6.3 pints. For 9 through 15 Ton

light commercial scroll compressors is 7 pints. For a 15

and 20 Ton large commercial scroll compressors (80 to

120 ton units), use 14.2 pints.

Compressor Crankcase Heaters

Table 35. Heater information