User Guide

SERVICING
36
Wiring is subject to change. Always refer to the wiring diagram on the unit for the most up-to-date wiring.
S-104 CHECKING COMPRESSOR
EFFICIENCY
The reason for compressor inefficiency is broken or damaged
suction and/or discharge valves, or scroll flanks on Scroll com-
pressors, reducing the ability of the compressor to pump re-
frigerant 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 - replace
the compressor.
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 refrigerant to
the compressor.
The illustration below shows typical heatpump TXV/check valve
operation in the heating and cooling modes.
COOLING HEATING
TXV VALVES
Some TXV valves contain an internal check valve thus eliminat-
ing 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 su-
perheat spring in the valve.
0% bleed type expansion valves are used on indoor and out-
door coils. The 0% bleed valve will not allow the system pres-
sures (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 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 can-
not 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 OP-
TIMUM PRODUCT OPERATION. DO NOT USE SUBSTI-
TUTES.
S-106 OVERFEEDING
Overfeeding by the expansion valve results in high suction pres-
sure, cold suction line, and possible liquid slugging of the com-
pressor.
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.
S-108 SUPERHEAT
The expansion valves are factory adjusted to maintain 15 to 18
degrees superheat of the suction gas. Before checking the
superheat or replacing the valve, perform all the procedures
outlined under Air Flow, Refrigerant Charge, Expansion 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 ex-
isting pressure. See Temperature - Pressure Chart on follow-
ing pages.
S-109 CHECKING SUBCOOLING
Refrigerant liquid is considered subcooled when its tempera-
ture is lower than the saturation temperature corresponding to
its pressure. The degree of subcooling equals the degrees of
temperature decrease below the saturation temperature at the
existing pressure.