SERVICING
20
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
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.
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.
Testing Start Relay Kits
Testing Coil Relay
1. Disconnect power to unit
2. Disconnect all wiring
3. Measure the resistance of the coil between terminals
2 & 5
4. If the coil reads open or shorted, replace the relay
Testing Contacts Resistance
1. Disconnect power to unit
2. Disconnect all wiring to the start relay
3. Measure the resistance of the contacts between
terminals 1 & 2
4. If the contacts read open, replace the relay
Testing Contacts Voltage
1. With power on, provide a call for cool to energize the
compressor
2. With the compressor running, use a voltmeter to
measure the voltage between terminals 1 & 2
3. voltage reading of zero indicates that the relay’s
contacts are stuck, replace the relay
Two quick ways to test a capacitor are a resistance and a
capacitance check.
Capacitance Check (MFD)
WARNING
Discharge capacitor through a 20 to 30 OHM resistor before
handling.
1.
Turn Power off to Unit
2.
Discharge capacitor through a 20Ω - 30Ω resistor
3. Remove wires from capacitor
4. Use multi-meter check micro-farads (MFD) of the
capacitor.
5. Place leads from C – HERM
