GPG14M Service Manual

SERVICING
38
The low pressure control is designed to cut-out (open) at
approximately 7 PSIG ± 3 PSIG. It will automatically cut-in
(close) at approximately 25 PSIG ± 5 PSIG.
Test for continuity using a VOM and if not as above, replace
the control.
S-15 CHECKING CAPACITOR
CAPACITOR, RUN
A run capacitor is wired across the auxiliary and main
windings of a single phase permanent split capacitor motor.
The capacitors primary function is to reduce the line current
while greatly improving the torque characteristics of a motor.
This is accomplished by using the 90° phase relationship
between the capacitor current and voltage in conjunction with
the motor windings so that the motor will give two phase
operation when connected to a single phase circuit. The
capacitor also reduces the line current to the motor by
improving the power factor.
CAPACITOR, START
SCROLL COMPRESSOR MODELS
Hard start components are not required on Scroll compres-
sor equipped units due to a non-replaceable check valve
located in the discharge line of the compressor. However
hard start kits are available and may improve low voltage
starting characteristics.
This check valve closes off high side pressure to the com-
pressor after shut down allowing equalization through the
scroll flanks. Equalization requires only about one or two
seconds during which time the compressor may turn back-
wards.
Your unit comes with a 180-second anti-short cycle to
prevent the compressor from starting and running back-
wards.
MODELS EQUIPPED WITH A HARD START DEVICE
A start capacitor is wired in parallel with the run capacitor to
increase the starting torque. The start capacitor is of the
electrolytic type, rather than metallized polypropylene as
used in the run capacitor.
A switching device must be wired in series with the capacitor
to remove it from the electrical circuit after the compressor
starts to run. Not removing the start capacitor will overheat
the capacitor and burn out the compressor windings.
These capacitors have a 15,000 ohm, 2 watt resistor wired
across its terminals. The object of the resistor is to discharge
the capacitor under certain operating conditions, rather than
having it discharge across the closing of the contacts within
the switching device such as the Start Relay, and to reduce
the chance of shock to the servicer. See the Servicing
Section for specific information concerning capacitors.
S-9 CHECKING FAN RELAY CONTACTS
The fan relays are incorporated into the control board. See
section S-313 for checking control board.
S-12 CHECKING HIGH PRESSURE CONTROL
HIGH VOLTAGE!
Disconnect ALL power before servicing
or installing this unit. Multiple power
sources may be present. Failure to do so
may cause property damage, personal injury
or death.
The high pressure control senses the pressure in the liquid
line. If abnormally high condensing pressures develop, the
contacts of the control open, breaking the control circuit
before the compressor motor overloads. This control is
automatically reset.
1. Using an ohmmeter, check across terminals of high
pressure control, with wire removed. If not continuous,
the contacts are open.
3. Attach a gauge to the dill valve port on the base valve.
With power ON:
4. Start the system and place a piece of cardboard in front
of the condenser coil, raising the condensing pressure.
5. Check pressure at which the high pressure control cuts-
out.
If it cuts-out at 660 PSIG ± 10 PSIG, it is operating normally
(See causes for high head pressure in Service Problem
Analysis Guide). If it cuts out below this pressure range,
replace the control. The control should reset at 420 PSIG ±
25 PSIG.
S-13 CHECKING LOW PRESSURE CONTROL
The low pressure control senses the pressure in the suction
line and will open its contacts on a drop in pressure. The low
pressure control will automatically reset itself with a rise in
pressure.