Scotsman HID312 Service Manual - Manual (Page 29)

HID312, HID525, HID540
Service Manual
April 2015
Page 29
Test Procedures - Refrigeration
The HID refrigeration system is steady-state. When
in operation and stabilized, it will maintain nearly
constant discharge and suction pressures.
Items that can affect that are:
• Irregular water flow
• Erratic thermostatic expansion valve
• Changes in room air temperature
Normally use of refrigeration gauges is unnecessary.
If the unit is making ice properly, it is highly likely that
all is normal. Refrain from attaching gauges, and
then only use very short hoses to avoid changing
the amount of refrigerant charge. See pressure
information on page 9.
The compressor gets its power from the contactor,
which is operated by the controller. It must be working
or the compressor will be off.
Compressor Starting
The HID312 uses a current relay for starting. The
HID525 and HID540 use a potential relay. Both have
start capacitors.
HID312 current relay: The contacts of a current relay
are normally open and close when the current is high.
They stay closed until the compressor starts and the
current drops off.
Compressor starts but current too high, overheats. If
the relay does not open the start winding will remain
powered and there will be current in the wire between
the start capacitor and the compressor. Replace the
relay.
Compressor does not start. Current relay contacts
may be open because relay coil is open, check for
continuity. Start capacitor may have failed.
HID525 or HID540 potential relay: The contacts of
this relay are normally closed and open when the
compressor starts.
Compressor starts but current too high, overheats. If
the relay contacts do not open, there will be current
from the start capacitor. Replace the relay.
Compressor does not start. Relay contacts open,
check for continuity. Replace relay if open. Start
capacitor may have failed.
Capacitor Testing
Capacitors may be tested using a multimeter, but
begin with a visual test. A good indication of a failed
capacitor is one that is bulging or leaking.
If the capacitor looks ok, check it with a multimeter.
1. Discharge the capacitor.
2. Set a digital meter to a high resistance scale of at
least 4k.
3. Put the probes on the capacitor terminals and
observe the display. It should provide a reading
and then show Open Line. If no reading, the
capacitor has failed and should be replaced.
If the meter has a Capacitance setting, use it to
measure the capacitance, replace if not near to the
mfd listed on it.
Compressor Testing
Because the compressor is the hermetic type, the
available testing methods are limited. Some items that
can be measured are winding resistance and amp
draw.
If the compressor does not start and a check with an
amp meter shows it does not draw any current, it is
likely it has an open winding or overload. Those can
be checked using a multimeter.
If the compressor is hot the overload may be open. An
open overload is an indication of a worn compressor,
defective starting components or high superheat.
Note: Normal operating temperature of the
compressor dome is 85 - 95 degrees F. - warm to the
touch.
If the overload is open and the compressor is not hot,
the overload itself could be the problem. Overloads
also open due to high current and a shorted winding
could cause that. Check for shorted or grounded
windings with a multimeter.
High superheat is caused by lack of refrigeration,
possibly from low charge or a TXV starving the
evaporator.