Carrier 38AQS016 Specifications download pdf (Page 19)

8. Backseat (open) compressor vapor and discharge valves.

Now close valves one turn to allow refrigerant pressure to

reach test gages.

Preliminary Charge

Before starting the unit, charge liquid refrigerant into the

high side of the system through the liquid service valve. Allow

high and low side pressures to equalize before starting com-

pressor. If pressures do not equalize readily, charge vapor on

low side of system to assure charge in the evaporator. Refer to

GTAC II, Module 5, Charging, Recovery, Recycling, and Rec-

lamation for liquid charging procedures.

Liquid Line Solenoid — To minimize refrigerant migra-

tion to the compressor during the heat pump OFF cycle, the

38AQ,ARQ unit must have a bi-flow liquid line solenoid valve

(field supplied). The valve opens when the compressor is ener-

gized, and closes when the compressor is deenergized. This

reduces compressor flooded starts, thus significantly increasing

compressor life.

Accumulator — The unit accumulator controls the rate of

liquid refrigerant to the compressor during heat pump operation.

The 38AQS accumulator features a unique method for

returning oil to the compressor. The oil return mechanism is

external to the accumulator. The mixture of oil and refrigerant

is metered to the compressor by a brass orifice which is remov-

able and cleanable. The oil return mechanism also contains a

solenoid valve that opens when the compressor is ON and

closes when the compressor is OFF. This keeps the liquid

refrigerant stored in the accumulator from draining to the

compressor during the heat pump OFF cycle, which further

protects the compressor against flooded starts.

START-UP

Compressor Rotation (38AQ,ARQ Units) —

3-phase units with scroll compressors, it is important to be cer-

tain compressor is rotating in the proper direction. To determine

whether or not compressor is rotating in the proper direction:

1. Connect service gages to suction and discharge pressure

fittings.

2. Energize the compressor.

3. The vapor pressure should drop and the discharge pres-

sure should rise, as is normal on any start-up.

If the vapor pressure does not drop and the discharge

pressure does not rise to normal levels:

1. Note that the condenser fan is probably also rotating in

the wrong direction.

2. Turn off power to the unit, tag disconnect.

3. Reverse any two of the unit power leads.

4. Reapply power to the compressor, verify correct pressures.

The vapor and discharge pressure levels should now move

to their normal start-up levels.

Compressor Overload — This overload interrupts

power to the compressor when either the current or internal

motor winding temperature becomes excessive, and automati-

cally resets when the internal temperature drops to a safe level.

This overload usually resets within 60 minutes (or longer). If

the internal overload is suspected of being open, disconnect the

electrical power to the unit and check the circuit through the

overload with an ohmmeter or continuity tester.

Advanced Scroll Temperature Protection

(ASTP) —

Advanced Scroll Temperature Protection

(ASTP) is a form of internal discharge temperature protection

that unloads the scroll compressor when the internal tempera-

ture reaches approximately 300 F. At this temperature, an inter-

nal bi-metal disk valve opens and causes the scroll elements to

separate, which stops compression. Suction and discharge pres-

sures balance while the motor continues to run. The longer the

compressor runs unloaded, the longer it must cool before the

bi-metal disk resets. See Fig. 17.

To manually reset ASTP, the compressor should be stopped

and allowed to cool. If the compressor is not stopped, the motor

will run until the motor protector trips, which occurs up to

90 minutes later. Advanced Scroll Temperature Protection will

reset automatically before the motor protector resets, which

may take up to 2 hours. A label located above the terminal box

identifies Copeland Scroll compressor models (ZR94, 108 and

125) that contain this technology. See Fig. 18.

The 38ARQ008 and 38ARQ012 units contain a 9 lb

(4.1 kg) charge of refrigerant. Add remainder of prelimi-

nary charge and allow pressure to equalize before starting

compressor. Failure to do so WILL cause the compressor

to overheat in a few minutes, possibly causing permanent

compressor damage. The amount of refrigerant added

must be at least 80% of the operating charge listed in

the Physical Data table (Tables 1A-1D).

Compressor crankcase heater must be on for 24 hours

before start-up. After the heater has been on for 24 hours,

the unit can be started.

Prior to starting compressor, a preliminary charge of refrig-

erant must be added to avoid possible compressor damage.

100

110

120

0 102030405060708090

Compressor Unloaded Run Time (Minutes)

Recommended Cooling Time

(Mi

nut

es)

*Times are approximate. Various factors, including high humidity,

high ambient temperature, and the presence of a sound blanket

will increase cool-down times.

Fig. 17 — Recommended Minimum Cool-Down

Time After Compressor is Stopped*

Fig. 18 — Advanced Scroll Temperature

Protection Label

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 31 32

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Carrier 38AQS016 Specifications Page 19

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