Service Manual

10
2. Capacitance testers are available which will read
value of capacitor. If value is not within 10 percent
value stated on capacitor, it should be replaced. If
capacitor is not open or shorted, the capacitance
value is calculated by measuring voltage across
capacitor and current it draws.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Exercise extreme caution when taking readings while
power is on.
!
WARNING
Use following formula to calculate capacitance:
Capacitance (mfd)= (2650 X amps)/volts
3. Remove any capacitor that shows signs of bulging,
dents, or leaking. Do not apply power to a defective
capacitor as it may explode.
Sometimes under adverse conditions, a standard run
capacitor in a system is inadequate to start compressor. In
these instances, a start assist device is used to provide an
extra starting boost to compressor motor. This device is
called a positive temperature coefficient (PTC) or start
thermistor. It is a resistor wired in parallel with the run
capacitor. As current flows through the PTC at start- up, it
heats up. As PTC heats up, its resistance increases greatly
until it effectively lowers the current through itself to an
extremely low value. This, in effect, removes the PTC from
the circuit.
After system shutdown, resistor cools and resistance value
returns to normal until next time system starts. Thermistor
device is adequate for most conditions, however, in systems
where off cycle is short, device cannot fully cool and
becomes less effective as a start device. It is an easy
device to troubleshoot. Shut off all power to system.
Check thermistor with ohmmeter as described below. Shut
off all power to unit. Remove PTC from unit. Wait at least 10
minutes for PTC to cool to ambient temperature.
Measure resistance of PTC with ohmmeter.
The cold resistance (RT) of any PTC device should be
approximately 100- 180 percent of device ohm rating.
12.5- ohm PTC = 12.5- 22.5 ohm resistance (beige color)
If PTC resistance is appreciably less than rating or more
than 200 percent higher than rating, device is defective.
A94006
Fig. 4 – Capacitors
Cycle Protector
ICP thermostats have anti- cycle protection built in to protect
the compressor. Should a non- ICP stat be utilized, it is
recommended to add a cycle protector to the system.
Solid- state cycle protector protects unit compressor by
preventing short cycling. After a system shutdown, cycle
protector provides for a 5  2- minute delay before
compressor restarts. On normal start- up, a 5- minute delay
occurs before thermostat closes. After thermostat closes,
cycle protector device provides a 3- sec delay.
Cycle protector is simple to troubleshoot. Only a voltmeter
capable of reading 24v is needed. Device is in control
circuit, therefore, troubleshooting is safe with control power
(24v) on and high- voltage power off.
With high- voltage power off, attach voltmeter leads across
T1 and T3, and set thermostat so that Y terminal is
energized. Make sure all protective devices in series with Y
terminal are closed. Voltmeter should read 24v across T1
and T3. With 24v still applied, move voltmeter leads to T2
and T3. After 5  2 minutes, voltmeter should read 24v,
indicating control is functioning normally. If no time delay is
encountered or device never times out, change control.
Crankcase Heater
Crankcase heater is a device for keeping compressor oil
warm. By keeping oil warm, refrigerant does not migrate to
and condense in compressor shell when the compressor is
off. This prevents flooded starts which can damage
compressor.
On units that have a single- pole contactor, the crankcase
heater is wired in parallel with contactor contacts and in
series with compressor. (See Fig. 5.) When contacts open, a
circuit is completed from line side of contactor, through
crankcase heater, through run windings of compressor, and
to other side of line. When contacts are closed, there is no
circuit through crankcase heater because both leads are
connected to same side of line. This allows heater to
operate when system is not calling for cooling. The heater
does not operate when system is calling for cooling.
TEMP SWITCH
BLK
2111
BLKBLKBLK
CRANKCASE HTR
A97586
Fig. 5 – Wiring for Single- Pole Contactor
For 3- phase 460V units, the CCH is controlled by a
temperature switch and relay. The relay is controlled by the
temperature switch that is wired in series with the low
voltage indoor transformer connections, R & C, from the low
voltage harness assembly. If the OD ambient is above 85 F,
the CCH switch is open and the relay will be de- energized.
In this state, the CCH will not be energized. If the OD
ambient goes below 65 F and doesn’t rise above 85 F, the
CCH switch is closed and the relay will be energized. In this
state, the CCH will be energized when the compressor
contactor is open.