ThermoForma 3771 - Compressor Installation

MAINTENANCE & REPAIR 39
Also check that the door seals properly. An air leak will
affect proper operation, and the cabinet’s ability to
reach its coldest temperature.
Run the cabinet at both 100% run, and a cycling tem-
perature for at least 24 hours. If the temperature and
pressures are correct, the system can be considered
repaired.
Hermetic systems should now have their process
stubs pinched off, hand valves removed and the ends
brazed shut.
COMPRESSOR INSTALLATION &
MAINTENANCE
TO CHANGE THE COMPRESSOR:
1. Disconnect the power supply to the cabinet.
2. Disconnect the power supply leads at the
compressor.
3. Disconnect wires to relay and capacitors.
4. Remove relay and starting capacitor and install on
new compressor.
5. Remove defective compressor from condensing unit
base.
6. Set new compressor in place.
7. Reconnect relay and capacitor wires.
8. Reconnect power supply lead.
9. Leak test, evacuate, and weigh in charge.
CHANGING DRIER
If flare connected, make sure flares and faces of fit-
tings on new drier are clean and in good condition
before installing new drier.
If sweat connected, clean tubing close to original drier
before cutting tubing in clean area. Check that ends of
the replacement drier are clean, then make brazed
connection using as little heat as possible.
Cut tubing only with tube cutters, not hacksaws, to
avoid metal filings from entering the system. Driers
must be replaced any time you enter the system,
except when you are obtaining pressures.
SERVICE VALVES
The compressors on some cabinets have service
valves for measuring suction and discharge pressures.
Two types are used. The first type is connected direct-
ly to the compressor body or shell and back seats to
connect gauges to the access port. The second
(Schrader type) is on the end of a process tube and
requires a gauge or charging line with a depressing
pin to open valve when the connection is made.
TO CHECK FOR OPEN WINDINGS
Use a multimeter. Measure ohms between “C” and “R”
and between “C” and “S.”
Add these values together. The resistance should equal
S to R
If there is no reading, the compressor winding or wind-
ings are open and the compressor should be replaced.
TO CHECK FOR
GROUNDED COMPRESSOR
Use multimeter. Touch probe from each terminal to an
unpainted surface of compressor body. If there is no
ground, there will be no change of the meter.
A reading indicates a ground and the compressor
should be replaced.
If there is voltage at the compressor terminals and the
compressor tries, but does not run, check voltage at
the compressor terminals while attempting to start the
compressor. If the voltage at the compressor terminals
is below 90% of the nameplate voltage, it is possible
the motor may not have developed sufficient torque to
start. Check to determine if:
A. Wire sizes are adequate.
B. Electrical connections are tight.
C. The circuit is not overloaded.
D. The power supply is adequate.
A defective relay or capacitor may prevent the com-
pressor starting.
TO CHECK OUT THE RELAY
1. Disconnect the cabinet from the power supply.
2. Remove the wires from the relay.
3. Touch probes to the contact terminals. Meter should
show infinity if closed.
4. Touch probes to the terminals of coil. The meter
should show a resistance reading.
If items 3 & 4 are O.K., the relay is good. If items 3 &
4 are not as indicated, change the relay.
WARNING
Be Careful Not to Touch Uninsulated
Parts of the Meter Probes.
CAUTION
This type valve should be tightly capped
except when making the gauge connection.