Carrier 26H - Manual (Page 47)

Carrier
S E R V I C E 26H
24. CAPACITORS
26H3
A 158-191 MFD capacitor, located on the compressor
above the terminal box, is used on the 26H3 115V
compressor.
26H5
A 243-270 MFD starting capacitor is used oh the
115 volt units. A 53-64 MFD capacitor is used on
the 230 volt units.
A capacitor may fail because of a shorf circuit or
an open circuit. If short circuited, the starting
current will be excessive.
The compressor may not start and will be responsi­
ble for blowing fuses or dimming lights. If fhe
capacitor wiring is open circuited, no current will
reach the starting winding and the compressor will
not start.
To check the starting capacitors, disconnect the
old capacitor and substitute a new capacitor. If
the unit storts,the old capacitor is faulty and should
be discarded.
25. RELAY
26H3
The current type relay is housed in the compressor
terminal box. It permits the compressor starting
winding to be energized for abouf 3/5 of a second
when the compressor is started. The locked rotor
surge of current energizes a magnetic coil closing
a set of contacts and completing the starting ca­
pacitor circuit to the compressor starting winding.
As the compressor speed increases, the initial
locked rotor current surge decreases, the magnetic
coil is de-energized, the contacts are opened, and
the starting capacitor circuit is removed from the
compressor starting winding.
26H5
The voltage type relay energizes the starting wind­
ing of the motor when the compressor is started
until it comes up to speed. After the motor comes
up to speed, the windings induce voltage back into
the starting circuit of the relay. This "back EMF"
is passed through a magnetic coil, which opens the
relay contacts an d cuts off the power to the starting
winding. When the compressor is stopped, a spring
pulls the contacts together again.
47
RELAY CONTACTS STUCK OPEN
If the relay fails with the contacts open, no current
will reach the starting windings. The compressor
will hum, but will not start. After 15 or 20 seconds,
the motor overload will cut off the power to the com­
pressor. After approximately 30 seconds, the over­
load will turn the power on again. If the relay
contacts are still open, the overload will cut off
the power again after another 15 or 20 seconds.
This cycle will repeat itself until the condition is
remedied. Replacement should be made immediately
since continued cycling may cause serious damage
to the unit. To test for relay contacts stuck open,
connect the power supply and turn the selector
switch to the "on" position. Momentarily touch a
jumper to relay terminals 1 and 2 on the H5, (3 and
the unmarked terminal on the H3) until the com­
pressor has a change to come up to speed. C A U ­
T I O N : Do not keep the jumper across these termi­
nals for more than an instant; otherwise, the start­
ing winding will be damaged.
RELAY CONTACTS STUCK CLOSED
If the relay fails with the contacts closed, the
starting windings will continue to be energized
after the compressor has come up to speed. The
compressor will start, but will run with a loud
grinding hum. After approximately eight seconds,
the overload will cut off the unit. Approximately
30 seconds later the overload will turn the power
on again. If the relay contacts still fail to open,
the overload will cut out after another eight seconds.
This cycle will repeat itself until the condition is
remedied.
To test for relay contacts which remain closed,
remove the nut from ferminal "S" on the compressor
terminal board. Connect the unit to the power
source and turn the selector switch to the "on"
position. As soon as the compressor has started,
immediately remove the wire from terminal "S".
If removal of the wire makes the unit operate
quietly, and without stopping, while attaching the
wire makes the unit operate noisily and cut off
on the overload, then the relay contacts are stuck
closed and the relay assembly should be replaced.
26. COMPRESSOR MOTOR OVERLOAD
Remove the top panel and the top of the compiessor
terminal box to reach the overload in the 26H5.
The 26H3 terminal box is accessible simply by re­
moving the front panel and terminal box cover.
26H-57PD