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SERVICING
S-12 CHECKING HIGH PRESSURE CONTROL
WARNING
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 capillary senses the pressure in the
compressor discharge 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.
2. Attach a gauge to the dill valve port on the base valve.
With power ON:
WARNING
Line Voltage now present.
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 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.
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 21 PSIG for heat pumps and 55 PSIG for air
conditioners. It will automatically cut-in (close) at approximately
50 PSIG for heat pumps and 95 PSIG for air conditioners.
Test for continuity using a VOM and if not as above, replace the
control.
S-14 CHECKING HIGH AND LOW PRESSURE
SWITCH VOLTAGE
The HPC and LPC are wired in series so output at both switches
should be the same when switches are closed voltage reading
should be 6.5 VDC or 8.0 VAC.
NOTE:
the Discharge Thermostat
is wired in series with the HPC if DT is open you will read input
voltage on the HPC and no voltage on the output of HPC or LPC.
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.
The line side of this capacitor is marked with “COM” and is wired
to the line side of the circuit.
S-15A RESISTANCE CHECK USING A DIGITAL
MULTI-METER
WARNING
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.
Check for Digital Test
1. Set the meter on Ohm range (Set it at lease 1000 Ohm =
1k).
