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4-19
valve (one complete turn will change the setting
approximately 1.7
_
C (3
_
F).
3. Reassemble the valve and then start the unit.
4. When the unit has stabilized operation for at
least 20 minutes, recheck superheat setting.
5. If superheat setting is correct, remove gauge and
thermocouple. Secure panel in position.
4.27 EVAPORATOR FAN MOTOR CAPACITORS
The two-speed evaporator fan motors are of the
permanent-split capacitor type. The motor is equipped
with one capacitor (used in the high speed circuit) and
another capacitor is used for the low speed circuit.
a. When to check for a defective capacitor
1. Fan motor will not change speed. For example:
controller settings above ---10
_
C (+14
_
F) cause the
motor to run in high speed.
Controller settings below ---10
_
C (+14
_
F) cause
the motor to run in low speed.
2. Motor running in wrong direction (after
checking for correct wiring application).
b. Removing the capacitor
WARNING
Make sure power to the unit is OFF and power
plug disconnected before removing capacitor(s).
1. The capacitor located on the motor and above
the evaporator fan deck may be removed by two methods:
(a)
If container is empty
, open upper, rear,
panel of the unit and capacitor may be serviced after
disconnecting power plug.
(b)
If container is full,
turn the unit power OFF
and disconnect power plug. Remove the #2 evaporator
fan motor access panel. (See Figure 1-1). Remove two
lower capscrews securing motor assembly to bracket and
then remove Ty-Raps from wire harness. Loosen two
upper capscrews on the fan motor assembly. Remove or
set aside motor to reach capacitors. With power OFF
discharge the capacitor and disconnect the circuit wiring.
c. Checking the capacitor
Three methods for checking capacitors are
:
(1) Direct replacement, (2) volt-ohmmeter, and (3)
capacitor analyzer.
1.
Direct replacement
of capacitor with one of the
same value.
2.
Volt-ohmmeter set on RX 10,000 ohms.
Connect
ohmmeter leads across the capacitor terminals and
observe the meter needle. If the capacitor is good, the
needle will make a rapid swing toward zero resistance and
then gradually swing back toward a very high resistance
reading.
If the capacitor has failed open, the ohmmeter
needle will not move when the meter probes touch the
terminals. If the capacitor is shorted, the needle will
swing to zero resistance position and stay there.
3.
Capacitor analyzer
The function of the analyzer is to read the
microfarad value of a capacitor and to detect insulation
breakdown under load conditions. The important
advantages of a analyzer is its ability to locate capacitors
that have failed to hold their microfarad ratings or ones
that are breaking down internally during operation. It is
also useful in identifying capacitors when their
microfarad rating marks have become unreadable.
4.28 HUMIDISTAT
a. Maintenance
Soiled sensing elements can be cleaned by dipping
the stem in soapy fresh water or fresh water with washing
powder (max. 80
_
C = 176
_
F).
When drying, the stem must remain tensioned, i.e.,
the set point knob is set to approximately 0% R.H.
Drying time approximately 24 hours. If necessary,
recalibrate the humidistat.
b. Setting
1. The upper switching point of switch
A
is set by
the set point knob
E
(See Figure 4-25).
2. In case of deviations of the measured humidity
from the set point, a recalibration by means of the nut (
S
)
is recommended:
E
S
A
Figure 4-25. Humidistat
3. If the actual value is higher than the set point,
turn nut (
S
) clockwise.
4. If the actual value is lower than the set point,
turn nut (
S
) counterclockwise.
Set Point
20%
40%
60%
70%
80%
1/6 turn ---
15%
15%
11%
8%
5%
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