Service Manual

9
ELECTRICAL
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or death.
Exercise extreme caution when working on any
electrical components. Shut off all power to system prior
to troubleshooting. Some troubleshooting techniques
require power to remain on. In these instances, exercise
extreme caution to avoid danger of electrical shock.
ONLY TRAINED SERVICE PERSONNEL SHOULD
PERFORM ELECTRICAL TROUBLESHOOTING.
!
WARNING
Aluminum Wire
UNIT OPERATION AND SAFETY HAZARD
Failure to follow this caution may result in equipment
damage or improper operation.
Aluminum wire may be used in the branch circuit (such
as the circuit between the main and unit disconnect),
but only copper wire may be used between the unit
disconnect and the unit.
CAUTION
!
Whenever aluminum wire is used in branch circuit wiring
with this unit, adhere to the following recommendations.
Connections must be made in accordance with the National
Electrical Code (NEC), using connectors approved for
aluminum wire. The connectors must be UL approved
(marked Al/Cu with the UL symbol) for the application and
wire size. The wire size selected must have a current
capacity not less than that of the copper wire specified, and
must not create a voltage drop between service panel and
unit in excess of 2 of unit rated voltage. To prepare wire
before installing connector, all aluminum wire must be
“brush- scratched” and coated with a corrosion inhibitor
such as Pentrox A. When it is suspected that connection will
be exposed to moisture, it is very important to cover entire
connection completely to prevent an electrochemical action
that will cause connection to fail very quickly. Do not reduce
effective size of wire, such as cutting off strands so that wire
will fit a connector. Proper size connectors should be used.
Check all factory and field electrical connections for
tightness. This should also be done after unit has reached
operating temperatures, especially if aluminum conductors
are used.
Contactor
The contactor provides a means of applying power to unit
using low voltage (24v) from transformer in order to power
contactor coil. Depending on unit model, you may encounter
single- or double- pole contactors. Exercise extreme
caution when troubleshooting as 1 side of line may be
electrically energized. The contactor coil is powered by
24vac. If contactor does not operate:
1. With power off, check whether contacts are free to
move. Check for severe burning or arcing on contact
points.
2. With power off, use ohmmeter to check for continuity
of coil. Disconnect leads before checking. A low
resistance reading is normal. Do not look for a
specific value, as different part numbers will have
different resistance values.
3. Reconnect leads and apply low- voltage power to
contactor coil. This may be done by leaving
high- voltage power to outdoor unit off and turning
thermostat to cooling. Check voltage at coil with
voltmeter. Reading should be between 20v and 30v.
Contactor should pull in if voltage is correct and coil is
good. If contactor does not pull in, replace contactor.
4. With high- voltage power off and contacts pulled in,
check for continuity across contacts with ohmmeter. A
very low or 0 resistance should be read. Higher
readings could indicate burned or pitted contacts
which may cause future failures.
Capacitor
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or equipment damage.
Capacitors can store electrical energy when power is
off. Electrical shock can result if you touch the capacitor
terminals and discharge the stored energy. Exercise
extreme caution when working near capacitors. With
power off, discharge stored energy by shorting across
the capacitor terminals with a 15,000- ohm, 2- watt
resistor.
!
WARNING
NOTE: If bleed resistor is wired across start capacitor, it
must be disconnected to avoid erroneous readings when
ohmmeter is applied across capacitor.
ELECTRICAL SHOCK HAZARD
Failure to follow this warning could result in personal
injury or equipment damage.
Always check capacitors with power off. Attempting to
troubleshoot a capacitor with power on can be
dangerous. Defective capacitors may explode when
power is applied. Insulating fluid inside is combustible
and may ignite, causing burns.
!
WARNING
Capacitors are used as a phase- shifting device to aid in
starting certain single- phase motors. Check capacitors as
follows:
NOTE: ECM motors do NOT use capacitors.
1. With power off, discharge capacitors as outlined
above. Disconnect capacitor from circuit. Put
ohmmeter on R X 10k scale. Using an analog
ohmmeter, check each terminal to ground (use
capacitor case). Discard any capacitor which
measures 1/2 scale deflection or less. Place
ohmmeter leads across capacitor and place on R X
10k scale. Meter should jump to a low resistance
value and slowly climb to higher value. Failure of
meter to do this indicates an open capacitor. If
resistance stays at 0 or a low value, capacitor is
internally shorted.