Manitowoc J-1300, Руководство по обслуживанию

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Section 6 Electrical System
6-45
CONTROL BOARD RELAYS
Function
The control board relays energize and de-energize
system components.
Specifications
Relays are not field replaceable. Old and new style
control boards use four control board relays. New
style control boards have a fifth relay which is not
used.
Check Procedure
To increase relay life, there is a capacitor and a
resistor mounted across the relay contacts to reducing
arcing. Keep this in mind when measuring voltage
through open relay contacts.
When measuring voltage through open contacts with
a component disconnected from the relay, the current
flows through the capacitor and resistor. This results
in a “line voltage” reading. The current through the
capacitor and resistor is milliamps. Always measure
voltage with the component connected to the relay
contacts which result in a “0” reading when the
contacts are open.
For example, a service technician turns the toggle
switch OFF (relay contact open) and unplugs the
water pump (component disconnected). The service
technician places the voltmeter leads into the water
pump plug (taking voltage through open contacts
with the component disconnected). He reads 208
volts (“line voltage” for the model being worked on).
The service technician mistakenly replaces the
control board, thinking that the relay is stuck closed.
Actually, there is nothing wrong with the relay, as the
technician was reading milliamp current flow through
the capacitor and resistor.
Remember to leave components connected to the
relays when taking voltage measurements. Otherwise,
the reading will always be “line voltage”, whether the
relay contacts are open or closed.