191 Rev. 3
SERVICING
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% bleed 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.
30% bleed valves used on some previous models will con-
tinue to allow some equalization even though the valve has
shut-off completely because of the bleed holes within the
valve. This type of valve should not be used as a replace-
ment for a 0% bleed valve, due to the resulting drop in perfor-
mance.
Good thermal contact between the feeler bulb and the suc-
tion line is essential to provide satisfactory valve control and
performance.
The bulb must be securely fastened with two straps to a
clean straight section of the suction line. Application of the
bulb to a horizontal run of line is preferred. If a vertical instal-
lation cannot be avoided, the bulb must be mounted so that
the capillary tubing comes out at the top.
All single phase reciprocating compressors must use a
hard start kit when matched with a expansion valve
indoor coil .
THE VALVES PROVIDED BY AMANA ARE DESIGNED TO
MEET THE SPECIFICATION REQUIREMENTS FOR OPTI-
MUM PRODUCT OPERATION. DO NOT USE SUBSTI-
TUTES.
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-26 Checking Expansion Valve Operation.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 12 to
18 degrees superheat of the suction gas. Before checking
the superheat or replacing the valve, perform all the proce-
dures outlined under Air Flow, Refrigerant Charge, Expan-
sion Valve - Overfeeding, Underfeeding. These are the most
common causes for evaporator malfunction.
CHECKING SUPERHEAT
Refrigerant gas is considered superheated when its tempera-
ture is higher than the saturation temperature corresponding
to its pressure. The degree of superheat equals the degrees
of temperature increase above the saturation temperature at
existing pressure. See Temperature - Pressure Chart.
1. Attach an accurate thermometer or preferably a thermo-
couple type temperature tester to the suction line at a
point at least 6" from the compressor.
2. Install a low side pressure gauge on the suction line ser-
vice valve at the outdoor unit.
3. Record the gauge pressure and the temperature of the
line.
4. Convert the suction pressure gauge reading to tempera-
ture by finding the gauge reading in Temperature - Pres-
sure Chart and reading to the left, find the temperature in
the °F. Column.
5. The difference between the thermometer reading and pres-
sure to temperature conversion is the amount of super-
heat.
EXAMPLE:
a. Suction Pressure = 84
b. Corresponding Temp. °F. = 50
c. Thermometer on Suction Line = 63°F.
To obtain the degrees temperature of superheat subtract 50.0
from 63.0°F.
The difference is 13° Superheat. The 13° Superheat would
fall in the ± range of allowable superheat.
SUPERHEAT ADJUSTMENT
The expansion valves used on Amana coils are factory set
and are not field adjustable. If the superheat setting becomes
disturbed, replace the valve.
