Thermostatic Expansion Valve; Overfeeding; Underfeeding - Daikin APGM3 Service And Troubleshooting

SERVICING
Checking Compressor Efficiency
The reason for compressor inefficiency is broken or
damaged scroll flanks on Scroll compressors, reducing the
ability of the compressor to pump refrigerant vapor.
The condition of the scroll flanks is checked in the following
manner.
1. Attach gauges to the high and low side of the system.
2. Start the system and run a "Cooling Performance Test.
If the test shows:
a. Below normal high side pressure.
b. Above normal low side pressure.
c. Low temperature difference across coil.
d. Low amp draw at compressor.
And the charge is correct. The compressor is faulty -
replace the compressor.

Thermostatic Expansion Valve

The expansion valve is designed to control the rate of liquid
refrigerant flow into an evaporator coil in exact proportion
to the rate of evaporation of the refrigerant in the coil. The
amount of refrigerant entering the coil is regulated since
the valve responds to temperature of the refrigerant gas
leaving the coil (feeler bulb contact) and the pressure of the
refrigerant in the coil.
This regulation of the flow prevents the return of liquid
refrigerant to the compressor.
The three forces which govern the operation of the valve
are: (1) the pressure created in the power assembly by the
feeler bulb, (2) evaporator pressure, and (3) the equivalent
pressure of the superheat spring in the valve.
0% bleed type expansion valves are used on the indoor
coils. The 0% valve will not allow the system pressures
(High and Low side) to equalize during the shut down
period. The valve will shut off completely at approximately
100 PSIG Pressure.
Good thermal contact between the feeler bulb and the
suction line is essential to satisfactory valve control and
performance.
The bulb must be securely fastened to a clean straight
section of the suction line. Application of the bulb to a
horizontal run of line is preferred. If a vertical installation
cannot be avoided the bulb should be mounted so that the
capillary tubing comes out at the top.
THE VALVES PROVIDED ARE DESIGNED TO MEET
THE SPECIFICATION REQUIREMENTS FOR OPTIMUM
PRODUCT OPERATION. DO NOT USE SUBSTITUTES.

Overfeeding

Overfeeding by the expansion valve results in high suction
pressure, cold suction line, and possible liquid slugging of
the compressor.
If these symptoms are observed:
1. Check for an overcharged unit by referring to the
cooling performance charts in the servicing section.
2. Check the operation of the power element in the valve
as explained in Checking Expansion Valve Operation.
3. Check for restricted or plugged equalizer tube.

Underfeeding

Underfeeding by the expansion valve results in low system
capacity and low suction pressures.
If these symptoms are observed:
1. Check for a restricted liquid line or drier. A restriction
will be indicated by a temperature drop across the
drier.
2. Check the operation of the power element of the valve
as described in Checking Expansion Valve Operation.
To prevent personal injury, carefully connect and
disconnect manifold gauge hoses. Escaping liquid
refrigerant can cause burns. Do not vent refrigerant to
atmosphere. Recover during system repair or final unit
disposal.
CAUTION
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