Amana R-410A Service Manual download pdf (Page 56)

SERVICING

b. If subcooling is low and superheat is high, add

charge to raise subcooling to 5 to 7 ºF then check

superheat.

c. If subcooling and superheat are high, adjust TXV

valve to 7 to 9 ºF superheat, then check subcooling.

d. If subcooling is high and superheat is low, adjust

TXV valve to 7 to 9 ºF superheat and remove

charge to lower the subcooling to 5 to 7 ºF.

NOTE: Do NOT adjust the charge based on suction

pressure unless there is a gross undercharge.

4. Disconnect manifold set, installation is complete.

Subcooling Formula = Sat. Liquid Temp. - Liquid Line Temp.

S-109B HEAT PUMP HEATING MODE

Hot Gas Method

System charge can be checked in the heating mode by

measuring the hot discharge gas at the compressor.

1. Allow the system to operate at least 20 minutes.

2. Attach and insulate an electronic thermometer probe to

the vapor service valve (large line) at the base valve.

3. Operate the system for 10 minutes.

4. Using an accurate electronic thermometer, measure the

temperature of the discharge gas at the probe and the

outdoor ambient temperature.

5. The temperature measured on the vapor service valve line

should be equal to the outdoor ambient temperature plus

110°F (± 4°). For example, if the outdoor ambient tem-

perature is 45°F, then the temperature measured by the

thermometer probe at the vapor service valve line should

be 155°F for a system that is properly charged. If the

temperature measured by the thermometer probe is

higher than the outdoor ambient plus 110°F, the system

charge should be adjusted by adding refrigerant to lower

the temperature. If the temperature measured is lower

than the outdoor ambient plus 110°F, the system charge

should be adjusted by recovering charge to raise the

temperature

NOTE: When adjusting the charge in this manner, allow

the system to operate for at least 10 minutes before

taking the next temperature reading.

S-110 CHECKING EXPANSION VALVE

OPERATION

1. Remove the remote bulb of the expansion valve from the

suction line.

2. Start the system and cool the bulb in a container of ice

water, closing the valve. As you cool the bulb, the suction

pressure should fall and the suction temperature will rise.

3. Next warm the bulb in your hand. As you warm the bulb,

the suction pressure should rise and the suction tempera-

ture will fall.

4. If a temperature or pressure change is noticed, the

expansion valve is operating. If no change is noticed, the

valve is restricted, the power element is faulty, or the

equalizer tube is plugged.

5. Capture the charge, replace the valve and drier, evacuate

and recharge.

S-111 FIXED ORIFICE RESTRICTOR DEVICES

The fixed orifice restrictor device (flowrator) used in conjunc-

tion with the indoor coil is a predetermined bore (I.D.).

It is designed to control the rate of liquid refrigerant flow into

an evaporator coil.

The amount of refrigerant that flows through the fixed orifice

restrictor device is regulated by the pressure difference

between the high and low sides of the system.

In the cooling cycle when the outdoor air temperature rises,

the high side condensing pressure rises. At the same time,

the cooling load on the indoor coil increases, causing the low

side pressure to rise, but at a slower rate.

Since the high side pressure rises faster when the tempera-

ture increases, more refrigerant flows to the evaporator,

increasing the cooling capacity of the system.

When the outdoor temperature falls, the reverse takes place.

The condensing pressure falls, and the cooling loads on the

indoor coil decreases, causing less refrigerant flow.

A strainer is placed on the entering side of the tube to prevent

any foreign material from becoming lodged inside the fixed

orifice restriction device.

If a restriction should become evident, proceed as follows:

1. Recover refrigerant charge.

2. Remove the orifice or tube strainer assembly and re-

place.

3. Replace liquid line drier, evacuate and recharge.

CHECKING EQUALIZATION TIME

During the "OFF" cycle, the high side pressure bleeds to the

low side through the fixed orifice restriction device. Check

equalization time as follows:

1. Attach a gauge manifold to the suction and liquid line dill

valves.

2. Start the system and allow the pressures to stabilize.

3. Stop the system and check the time it takes for the high

and low pressure gauge readings to equalize.

If it takes more than seven (7) minutes to equalize, the

restrictor device is inoperative. Replace, install a liquid line

drier, evacuate and recharge.

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Amana R-410A Service Manual Page 56

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