Diagnosing Start Components; Capacitor; Relay - Manitowoc Q270 Technician's Handbook

Diagnosing Start Components

If the compressor attempts to start, or hums and trips
the overload protector, check the start components
before replacing the compressor.

CAPACITOR

Visual evidence of capacitor failure can include a
bulged terminal end or a ruptured membrane. Do not
assume a capacitor is good if no visual evidence is
present. A good test is to install a known good
substitute capacitor. Use a capacitor tester when
checking a suspect capacitor. Clip the bleed resistor
off the capacitor terminals before testing.

RELAY

The relay has a set of contacts that connect and
disconnect the start capacitor from the compressor
start winding. The contacts on the relay are normally
open. The relay senses the voltage generated by the
start winding and closes and then opens the contacts
as the compressor motor starts. The contacts remain
open until the compressor is de-energized.
Part Number STH039 8/13 87