Overfeeding; Underfeeding; Superheat - Goodman ASX Service Instructions Manual

SERVICING
COOLING
TXV VALVES
Some TXV valves contain an internal check valve thus
eliminating the need for an external check valve and bypass
loop. 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 indoor and
outdoor 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 approxi-
mately 100 PSIG.
30% bleed valves used on some other models will continue
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 replacement for a 0%
bleed valve, due to the resulting drop in 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 installation
cannot be avoided, the bulb must be mounted so that the
capillary tubing comes out at the top.
THE VALVES PROVIDED BY GOODMAN ARE DESIGNED
TO MEET THE SPECIFICATION REQUIREMENTS FOR
OPTIMUM PRODUCT OPERATION. DO NOT USE SUB-
STITUTES.
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.
52
S-107 UNDERFEEDING
Underfeeding by the expansion valve results in low system
capacity and low suction pressures.
If these symptoms are observed:
HEATING
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 Opera-
tion.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 8 to
12 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 tem-
perature is higher than the saturation temperature corre-
sponding to its pressure. The degree of superheat equals the
degrees of temperature increase above the saturation tem-
perature at existing pressure. See Temperature - Pressure
Chart on following pages.