Evaporator Fan Motor Capacitors; When To Check For A Defective Capacitor; Removing The Capacitor; Checking The Capacitor - Carrier 69NT40-489-100 Series Operation And Service Manual

6.17 EVAPORATOR FAN MOTOR CAPACITORS

Units are equipped with one of 2 types of evaporator fan
motors, single, and dual capacitor. The evaporator fan
motors are of the permanent-split capacitor type.

6.17.1 When To Check For A Defective Capacitor

a. Fan motor will not change speed. For example: in the
conventional perishable mode, the motors should run
in high speed. In the economy perishable mode they
should switch speeds and in the frozen mode, the mo-
tors should run in low speed.
NOTE
The evaporator fan motors will always start in
high speed.
b. Motor running in wrong direction (after checking for
correct wiring application).
c. Motor will not start, and IP-EM's are not open.

6.17.2 Removing The Capacitor

WARNING
Make sure power to the unit is OFF and
power plug disconnected before removing
capacitor(s).
The capacitors are located on the motor and above the
evaporator fan deck they may be removed by two
methods:
1 If container is empty, open upper rear panel of the
unit. The capacitor may be serviced after discon-
necting power plug.
2 If container is full, turn the unit power OFF and dis-
connect power plug. Remove the evaporator fan
motor access panel. (See Figure 1, page 5). For
removal of the evaporator fan assembly, refer to sec-
tion 6.16, page 70.
WARNING
With power OFF discharge the capacitor
before disconnecting the circuit wiring.

6.17.3 Checking The Capacitor

If the capacitor is suspected of malfunction, you may
choose to simply replace it. Direct replacement requires
a capacitor of the same value. Two methods for
checking capacitor function are:
1. 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.
2. 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 are its ability to locate capacitors that have
failed to hold their microfarad ratings, or those that are
breaking down internally during operation. It is also
useful in identifying capacitors when their microfarad
rating marks have become unreadable.

6.18 SUCTION MODULATION VALVE

On start up of the unit, the valve will reset to a known
open position. This is accomplished by assuming the
valve was fully open, driving it fully closed, resetting the
percentage open to zero, then opening to a known 21%
staging position.
1
2-1/8 inch Nut
1. Suction Modulation Valve (SMV)
2. Stepper Drive (SD)

Figure 44. Suction Modulation Valve (SMV)

6.18.1 Precheck Procedure

a. Check unit for abnormal operation.
b. Check charge. If refrigerant is low repair as required
and again check operation.
c. If sufficient capacity cannot be maintained or unit is
tripping excessively on high pressure switch (HPS) in
high ambients, check coils and clean if required.
d. If capacity or control cannot be maintained turn unit
OFF, then back ON. This will reset the valve in the
event the controller lost communication with the
valve, and may correct the problem.
Carefully listen to the valve. During reset, the
valve will make a ratcheting noise that may be
heard or felt as it is attempting to close. If this
can be heard or felt, it indicates that the control-
ler and drive module are attempting to close the
valve, and may serve as a quick indication that
the drive module is in working order.
e. During the first few minutes of unit operation, com-
pressor reliability enhancement logic (CREL) may be
in effect. This places the valve at a 21% staging posi-
tion and is sufficient to drive the temperature of the
supply probe down several degrees during this inter-
val.
f. After the CREL time-out has been met, the valve will
start responding to the control logic and open or
close, relative to the demand. Scrutinize the unit op-
eration for a few minutes. While in pulldown the unit
will open the SMV to a maximum discharge pressure
of 325 psig in high ambient conditions, or as much as
the current setting and control logic will allow. The
current level should be high. A lower discharge pres-
sure will be seen in lower ambient temperatures.
Once the unit has reached set point, the SMV will go
71
2
NOTE
T-305