Welbilt FB081TF, Service Manual

Page: 75 / 96

Part Number REV00 04/08/2020 75
Section 7 Component Check Procedures
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 closed (start capacitor in
series with the start winding). The relay senses the voltage
generated by the start winding and opens the contacts as
the compressor motor starts. The contacts remain open
until the compressor is de-energized.
RELAY OPERATION CHECK
1. Disconnect wires from relay terminals.
2. Verify the contacts are closed.
Measure the resistance between terminals 1 and 2. No
continuity indicates open contacts. Replace the relay.
3. Check the relay coil.
Measure the resistance between terminals 2 and 5. No
resistance indicates an open coil. Replace the relay.
COMPRESSOR ELECTRICAL DIAGNOSTICS
Location
On the base unit behind the rear panels.
Specification
R-290 220-240/50 - 1/5HP, TL4CN
Check Procedure - The compressor does not start or will
trip repeatedly on overload
CHECK RESISTANCE (OHM) VALUES
Compressor windings can have very low ohm values. Use a
properly calibrated meter.
Perform the resistance test after the compressor cools. The
compressor dome should be cool enough to touch (below
120°F/49°C) to assure that the overload is closed and the
resistance readings will be accurate.
SINGLE PHASE COMPRESSORS
Disconnect power, then remove the wires from the
compressor terminals.
The resistance values between C and S and between C and
R, when added together, should equal the resistance value
between S and R.
If the overload is open, there will be a resistance reading
between S and R, and open readings between C and S and
between C and R. Allow the compressor to cool, then check
the readings again.
CHECK MOTOR WINDINGS TO GROUND
Check continuity between all three terminals and the
compressor shell or copper refrigeration line. Scrape metal
surface to get good contact. If continuity is present, the
compressor windings are grounded and the compressor
should be replaced.