Goodman [A/G]PG, Service Instructions Manual

SERVICING

31

S-15 CHECKING CAPACITOR

CAPACITOR, RUN

A run capacitor is wired across the auxiliary and main wind-
ings 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 re-
duces the line current to the motor by improving the power
factor.

CAPACITOR, START

SCROLL COMPRESSOR MODELS

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 characteris-
tics.

This check valve closes off high side pressure to the compres-
sor 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.

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 elec-
trolytic 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.

RELAY, START

A potential or voltage type relay is used to take the start ca-
pacitor out of the circuit once the motor comes up to speed.
This type of relay is position sensitive.  The normally closed
contacts are wired in series with the start capacitor and the
relay holding coil is wired parallel with the start winding.  As
the motor starts and comes up to speed, the increase in volt-
age across the start winding will energize the start relay hold-
ing coil and open the contacts to the start capacitor.

Two quick ways to test a capacitor are a resistance and a
capacitance check.

S-15A Resistance Check

1. Discharge capacitor and remove wire leads.

Discharge capacitor through a 20 to 30 OHM resistor
before handling.

Ca

p

aci

to

r

Volt / Ohm
    Meter

TESTING CAPACITOR RESISTANCE

2. Set an ohmmeter on its highest ohm scale and connect

the leads to the capacitor -

A. Good Condition - indicator swings to zero and slowly
returns to infinity.  (Start capacitor with bleed resistor will
not return to infinity.  It will still read the resistance of the
resistor).

B. Shorted - indicator swings to zero and stops there -
replace.

C. Open - no reading - replace.  (Start capacitor would read
resistor resistance).

S-15B Capacitance Check

Using a hookup as shown below, take the current and voltage
readings and use them in the formula:

Discharge capacitor through a 20 to 30 OHM resistor
before handling.

Capacitance (MFD) = 2650 X Current

Voltage