SERVICING
52
NOTE: THIS CHARGING PROCEDURE CAN ONLY BE
DONE IN THE COOLING MODE OF OPERATION. ALL
MODELS WITH COMPRESSOR PROCESS TUBE ACCESS
VALVE CAN BE PROCESSED IN HEATING CYCLE IF THIS
VALVE IS USED.
Units having capillary tubes or flow control restrictors can be
checked against the Desired Superheat vs. Outdoor Tem-
perature Chart in this section. Coils with thermostatic ex-
pansion valves (TXV's) must be checked by subcooling. See
"Checking Subcooling and Superheat" sections in this
manual.
If a restriction is located, replace the restricted part, replace
drier, evacuate and recharge.
S-104 CHECKING COMPRESSOR EFFICIENCY
The reason for compressor inefficiency is broken or dam-
aged suction and/or discharge valves, or scroll flanks on Scroll
compressors, reducing the ability of the compressor to pump
refrigerant vapor.
The condition of the valves or 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-
⇒ Below normal high side pressure.
⇒ Above normal low side pressure.
⇒ Low temperature difference across coil.
⇒ Low amp draw at compressor.
-and the charge is correct. The compressor is faulty - re-
place the compressor. NOTE: THIS TEST CANNOT BE
DONE IN THE HEATING MODE
S-105 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 refriger-
ant 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 suc-
tion line is essential to satisfactory valve control and perfor-
mance.
The bulb must be securely fastened to a clean straight sec-
tion 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 BY AMANA
®
BRAND ARE DE-
SIGNED TO MEET THE SPECIFICATION REQUIREMENTS
FOR OPTIMUM PRODUCT OPERATION. DO NOT USE
SUBSTITUTES.
S-106 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 S-110 Checking Expansion Valve Operation.
3. Check for restricted or plugged equalizer tube.
S-107 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 S-110 Checking Expansion Valve Operation.
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