Troubleshooting Pcb; Troubleshooting Icm2 - Carrier FA4ANF Service Manual

airflow. This profile will minimize cold blow in heat pump
operation and could enhance system efficiency.
4. ENH, enhanced selection provides a 30 sec on/180 sec off
delay at half airflow, adding comfort and efficiency.
Step 5—Troubleshooting PCB
Use Fig. 17 and 18 and Tables 3, 4, and 5 as guides in
troubleshooting PCB unless otherwise noted.
IF FAN WILL NOT TURN ON FROM THERMOSTAT:
If There Is No High Voltage To PCB:
1. Check connection of 12-pin plug from heaters to receptacle on
Easy Select board. This supplies power to PCB. Be sure plug
is connected properly.
2. Check sequencer number 1 and plug wiring. Yellow wire
should be connected to pin number 9 of plug and to limit
switch. Black wire should be connected to pin number 7 of
plug and to sequencer number 1.
3. Check power leads L1 and L2. If these are not receiving
power, system cannot function.
If PCB Has High Voltage Applied To It:
1. Check low-voltage transformer leads (red and brown). Be sure
they are wired to correct locations. (See Fig. 16
and 18.)
2. Check output voltage of transformer secondary side SEC2 and
SEC1. Be sure transformer output is around 24 vac. If
transformer output is zero vac and transformer is receiving
correct input voltage (208v or 240v), then transformer needs
to be replaced with recommended transformer. If transformer
output is 24 vac, proceed to items 3 and 4.
3. Check low-voltage fuse shown in Fig. 16. If fuse is blown,
replace it. The transformer cannot supply power to board with
fuse blown or loose. If fuse blows when unit has power
applied to it, the system most likely has 1 of the following
problems:
a. Check control circuit for a short or miswiring problem.
b. The maximum load on transformer is 40 VA. If load on
transformer is excessive, the low-voltage 5-amp fuse will
blow to protect transformer. If load exceeds VA rating of
transformer, a larger VA rated transformer needs to be
installed. Check sequencers for excessive current draw.
c. Check wiring of heaters. If a heater is miswired, fuse may
blow. If a heater is miswired, correct miswiring.
4. Check T1, T2, and T3 connections on primary side of
transformer. If they are not connected properly, low-voltage
terminal board cannot supply 24-v signal to energize fan
motor. If transformer is receiving correct primary voltage but
is not putting out correct secondary voltage, transformer needs
to be replaced.
IF ELECTRIC HEAT STAGES WILL NOT TURN ON BUT
FAN WILL TURN ON:
1. Check wiring of sequencers. Pay particular attention to high-
and low-voltage wiring of sequencers.
2. Check plug wiring to make sure that it is wired correctly.
3. Check voltage to sequencer. Sequencer number 1 receives a
24-vac signal. If it is receiving correct voltage, check to see if
sequencer is closing. If sequencer is not closing but is
receiving correct voltage, replace sequencer. If sequencer is
closing, check high-voltage wiring as discussed in items 1 and
2.
If There Are Blown Diodes:
If diodes are blown, it is probable that electric heater plug is
miswired. Correct miswiring.
NOTE: Board will need to be replaced if diode is bad.
If Traces Are Overheated on Back of PCB:
Usually whenever there is a trace blown on PCB, it means either
there has been a high-voltage short or high voltage has been
applied to low-voltage circuit. This can be prevented by making
sure PCB is wired correctly before PCB has power applied to it.
IF PCB FUSE KEEPS BLOWING:
When low-voltage fuse blows, it means transformer would have
blown if fuse had not been in circuit to protect it. The fuse usually
blows when there is a high current drawn on transformer, high
voltage applied to low-voltage circuit, or a direct secondary short.
When there is a high current drawn on transformer, it is most likely
because transformer has been shorted or system is trying to draw
more VA than transformer rating allows. When fuse blows because
of high voltage, the system has mixed high- and low-voltage
signals.
1. Check transformer and thermostat wiring. (See Fig. 16 and
18.) Be sure transformer is not shorting out because thermostat
wires are miswired.
2. Check wiring of sequencers. (See Fig. 16 and 18.) Be sure
low-voltage and high-voltage wiring are connected to proper
sequencers.
3. Check VA draw on transformer. If VA draw is more than VA
rating of transformer, fuse will blow. If this is the case, replace
transformer with one that has a higher VA rating and meets
system specifications.
Step 6—Troubleshooting ICM2 Fan Motor
IF MOTOR DOES NOT RUN:
1. With power turned off, check all plugs and receptacles on
circuit board and at motor for any deformation that may cause
a bad connection. Be sure all plugs are placed fully seated.
2. Verify that there are approximately 230v at terminals M1 and
M2. If not, determine if high voltage is entering board. It
enters through black and yellow wires at pins 7 and 9 in 12-pin
plug.
3. Verify that there is a low-voltage control signal to motor. The
motor receives its control signals through the 7-pin motor plug
P2. The voltage output of each pin in plug will be different for
each mode of operation. Table 6 lists circuit board screw
terminals that have 24 vac present (powered by thermostat)
and lists voltage that is present at each pin of 7-pin plug for
each operating mode. Tests should be taken between points
listed and common (C screw terminal). If all values of any 1
of operating modes checks OK and motor fails to run, then
motor is defective and should be replaced.
IF MOTOR DOES NOT RUN SMOOTHLY:
First verify that the cause is not an out-of-balance or damaged
blower wheel. If it is not blower wheel, motor is defective and
should be replaced.
IF MOTOR SHAFT DOES NOT ROTATE SMOOTHLY:
When manually turning shaft of ICM, the shaft does not rotate
smoothly. The shaft has steps during rotation referred to as motor
cogging. The cogging is caused by permanent magnets passing
each pole of motor. However, shaft should not require excessive
force to turn. If shaft is VERY difficult to turn, motor control or
bearings have failed and motor must be replaced.
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