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SERVICING
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
discharge line. If abnormally high discharge 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.
2. Attach a gauge to the access fitting on the liquid line.
With power ON:
3. Start the system and place a piece of cardboard in
front of the condenser coil, raising the condensing
pressure.
4. 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.
The low pressure control is designed to cut-out (open) at
approximately 22 PSIG ± 7 PSIG. It will automatically cut-in
(close) at approximately 50 PSIG ± 7 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 (Single Phase Compressors
Only)
Hard start components are not required on Scroll
compressor 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
compressor after shut down allowing equalization through
the scroll flanks. Equalization requires only about one or
two seconds during which time the compressor may turn
backwards.
Your unit comes with a 180-second anti-short cycle
to prevent the compressor from starting and running
backwards.
51
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