Service manual

48TD 204
defective. The overload protector, start and/or run capacitor, relay,
circuit board, safety controls, etc.
1. Check voltage at compressor terminals. NO voltage
will require checking the electrical circuit working
back from the compressor to determine where the volt-
age supply is interrupted and correct as required. The
load voltage, while compressor is trying to start,
should not be less than 90% of rated required voltage.
Line voltage and wire size effect the life expectancy of the electrical
components, compressor, motor winding, solenoid coils, etc.
Poor line quality voltage will cause many erratic electrical prob-
lems. Remember every electrical product, ice machine, dispenser,
walk–in, reach–in, air conditioner, etc. required proper power sup-
ply to operate. Be certain when voltage checks are performed that
you are measuring load voltage, not line voltage.
2. A defective capacitor or start relay may prevent the
compressor from starting. Should the compressor at-
tempt to start, but is unable to do so, or if the compres-
sor hums or trips off on the over protector, check the
following:
NOTE: For 50 HZ application on dual rated 50/60 HZ mod-
els, load voltage while compressor is starting must
not be less than 90% of 50 HZ rating.
Relay
Potential –
For the potential type, contacts are normally closed. The start con-
tacts open by C.E.M.F. generated by the compressor at approximate-
ly 80% of the normal operating speed. As the contacts open, only the
start capacitor is removed from the start circuit. Both the start and
run winding and the run capacitor remain in the circuit. This relay
may or may not be directional in mounting.
Current –
For the current type, contacts are normally open. The start contacts
close by the high current draw from the locked rotor condition with
only the run winding in the circuit. As the contacts close, the start
capacitor and the start winding is energized and the compressor
starts. At approximately 80% of its operating speed the current draw
drops off, the relay contacts open removing the start winding and
start capacitor from the circuit. Remember, current relays are direc-
tional in their mounting to allow contacts to lift and close.
Capacitors
A quick check is to replace suspected defective capacitors with
known good capacitors being careful to stay within the range for
substitute values. Should those values be unknown, a basic rule for
capacity is: for start capacitors 10% and run capacitors 5% of