SERVICING
25
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
characteristics.
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
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.
RELAY, START
A potential or voltage type relay is used to take the start
capacitor 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
voltage across the start winding will energize the start relay
holding 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
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.
1. Discharge capacitor and remove wire leads.
WARNING
Discharge capacitor through a 20 to 30 OHM
resistor before handling.
OHMMETER
CAPACITOR
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 amperage and
voltage readings and use them in the formula:
VOLTMETER
CAPACITOR
AMMETER
15 AMP
FUSE
TESTING CAPACITANCE
Summary of Contents for DCH048 SERIES
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Page 133: ...38 DCC COMMERCIAL 15 25 Ton Packaged Air Conditioner Unit WIRING DIAGRAMS...
