Service manual

26
Installation and Service Manual
COMPONENT DIAGNOSTICS
DIAGNOSIS OF SERVEND CUBER THERMISTOR
Erratic Operation (Bridge Thickness Erratic):
1. Check thermistor mounting:
A) Are the wire leads to the circuit board secure?
B) Is the tip of the control flush or protrude 1/64"
(.4mm) beyond the lower evaporator extrusion?
If correctly mounted, you may feel a slight bump.
C) Is there a heavy film of sealant over the tip of the
control? A very slight film is OK. If the tip of the control
looks a milky color, the silicone is too thick.
D) After the machine sets for 24 hours is the first
sheet of ice OK? Does each succeeding sheet
of ice get thinner? This could be a sealing prob-
lem with water in the sensor well.
2. Bridge thickness gets progressively thinner each cycle:
A) Thermistor not properly sealed in lower evapo-
rator molding or thermistor set too far back into
molding.
B) To Reseal:
1. Remove water pan
2. Reach up in back of evaporator and
grasp thermistor leads and remove ther-
mistor. Use a 1/16" punch to push ther-
mistor out.
3. Remove dried silicone adhesive from
thermistor and clean out opening in
evaporator molding.
4. If replacing a plastic sleeve thermistor
with a metal jacket thermistor hole will
have to be reamed to 11/64" (.43cm). Do
not use a power drill.
5. Force G.E. RTV-108* silicone adhe-
sive into front opening of evaporator
molding filling the hole until silicone
come out the back. Place thumb or fin-
ger over opening and reinsert thermistor
from rear of opening pushing toward the
front of the evaporator modling (this will
force silicone around the thermistor as
you push thermistor forward giving a
positive seal). Allow thermistor to be
flush or protrude approximately 1/64"
(.4mm) beyond face of evaporator mold-
ing with ample amount of silicone
ahesive. (1/64" equals a very slight
bump).
6. The G. E. RTV-108 silicone will set,
tack-free, in aproximately 15 minutes. Do
not allow water to contact silicone
until it is tack free.
*This is the only silicone recommended for proper
sealing of thermistor by Servend International (part
#5000881, or purchase locally.
Check Procedure:
1. Clear the evaporator of any ice. This can be done
with the use of the manual harvest switch on the circuit board.
2. Place the machine in the ice mode. Allow the
unit to make one sheet of ice.
3. At the end of a regular freeze time, manually har-
vest the ice.
4. Observe the sheet of ice. Is the bridge thickness
even from the top to bottom? Is the bridge thinner at the
top than at the bottom?
5. If your sheet of ice is thinner at the top than at
the bottom, your machine is suffering from a water loss
or refrigeration problem.
6. If you ice has an even bridge from top to bottom,
proceed with the OHM meter check.
7. Remove the control wires from the EV terminals
on the circuit board. In a dual evaporator machine, only
the left control (connected to the EV terminals) deter-
mines the thickness of the ice.
8. Attach you OHM meter to the ends of the wires.
Do not remove the control from the evaporator extru-
sion. Your meter should be capable of reading 5,000 to
40,000 OHMs accurately.
9. At room temerature, your control should read
ABOUT 10,000 to 15,000 OHM resistance.
10. Place an ice cube on the tip of the control. You
should obtain a reading in the range of 25,000 to 36,000
OHMs.
11. These readings are approximate. Do not be con-
cerned if your reading are slightly different.
12. If your control responds comparable to the above
readings, this control is good. If your control does not
respond, replace the control.
13. If you are working with a 4 relay circuit board
and the ice sensing control is "open" or "shorted", the
power light on the circuit board will flash. The machine
will not operate.