SERVICING
38
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 610 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.
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.
THREE PHASE
Using a voltmeter, test across terminals.
A.
L1-L2, L1-L3, and L2-L3 - If voltage is present,
proceed to B. If voltage is not present, check breaker
or fuses on main power supply..
B.
T1-T2, T1-T3, and T2-T3 - If voltage readings are not
the same as in "A", replace contactor.
VOLT/OHM
METER
CC
Ohmmeter for testing holding coil
Voltmeter for testing contacts
T1
L1
T3
L3
T2
L2
TESTING COMPRESSOR CONTACTOR
(ThreePhase)
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:
