Bryant FA4A - Manual (Page 13)

AUG/14/2008/THU 03:48 PM UTC TECH PUB FAX No. 317 240 5662 P. 013
TABLE e—МОТОВ CONTROL TEST VALUES
OPERATING MODE
SCREW TERMINALS
HAVING 24 VAC
VOLTAGES—7-PIN PLUG P2
W
Pin 1
Q
Pin 2
C
Pln3
c
Pin 4
R
Pin 5
Y/Y2
Pin 6 Y
Pin 7
Electric Heating R W2 W3* E* 24 vde 0 0 0 £4 vac 0
1-Speed A/C Cooling R Y/Y2 G 0 £4 vac , 0 0 24 vec 24 vac 0
2-Speed A/C, Low Speed Cooling R Y1 Q 0 £4 vac 0 0 24 vac 0 24 vac
S-Speed A/C, High Speed Cooling R Y/Y2 G 0 24 vac 0 0 24 vac 24 vac 0
1-Speed HP Cooling R Y/Y2 G 0 □ £4 vac □ 0 £4 vac 24 vac d
1-Speed HP Heating R Y/Y2 G 0 24 vac 0 0 24 vac 24 vac 0
2-Speed HP, Lew Speed Cooling R Y1 G 0 0 £4 vac 0 0 24 vac 0 24 vac
2-5peed HP, Low Speed Heating R Yi G 0 24 vac 0 0 £4 vac 0 24 vac
2-Speed HP, High Speed Cooling R Y/Y2 Y1 G 0 0 24 vac 0 0 24 vac 24 vac 24 vac
2-Speed HP, High Speed Heating R Y/Y2 YI Q 0 24 vac □ 0 24 vac 24 vac 24 vac
ContinuDue Fan R 0 24 vac 0 0 24 vac Q 0
Pin 1 @ 24 vdc with or without jumpers when ever any Individual heeter input or any combination of heater inputs are energized.
C. 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 fransforaier, 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 levy-voltage
signals,
1. Check transformer and thermostat wiring. (See Fig. 6 and
8,) Be Sure transformer is not shorting out because thermo­
stat wires are miswired,
2. Check wiring of sequencers. (See Fig. 6 and 8,) Be sure
low-voltage and high-voltage wiring are connected to
proper sequencers.
3. Check va draw o.n 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,
VI. TROUBLESHOOTING ICM2 FAN MOTOR
A. If Motor Does Not Run:
1. With power turned off, check all plugs and receptacles on
circuit board and at motor for any defonnation that may
cause a bad connection. Be sure all plugs are placed fully
seated.
%. Verify that there are approximately 230v at terminals Ml
apd Iyf2.,lf not, determine if high voltage is entering board.
It enters through black and yellow wires at pins 7 and ? in
12-pin plug.
3, Verify that there is a low-voltage control signal to motor.
The motor receives its contml signals through the 7-pin
mQ,tor 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,
B. If Motor Does Not Run Smoothly;
First verify that the cause is not an out-of-balapce or damaged
blower wheel. If it is not blower wheel, motor is defective and
should be replaced.
C. 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 and is 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.
D. If Motor Does Not Stop Running
1. Check for good ground between motor ground lead and
transformer common lead.
2. If motor continues to nin, remove all thermostat wires. If
motor stops, replace circuit board.
3. If motor continues to run, remove the 7-pin plug. If motor
continues to run, replace motor.
VII. CONDENSED VERSION OF TROUBLESHOOTING
FK4B MOTOR AND CONTROLS
This section provides a quick summary of how to troubleshoot the
FK4B. If more information is needed, refer to appropriate sections
of this service manual.
+ MOTOR
- If motor is hard to turn manually, replace motor.
- If motor docs not. run, check the components listed below
according to their instructions.
■- If motor runs in some operation modes and not in others,
check for a good ground connection between motor ground
lead and circuit board screw marked "ground screw" and
check the room thermostat and wiring harness according to
instructions listed
below.
- If motor does not stop running, remove the 7-pin plug from
circuit board. If motor continues to run, replace motor. If
motor stops running,''it is either the circuit board or thermo­
stat causing the problem. Test whether thermostat is at fault
by disconnecting it from the board.
+ CIRCUIT BOARD
- Check 5-amp fuse,
- Check for 230v between terminals Ml and M2. If m voltage
is present, check power to'board. 230-v power enters the
board through the black and yellow lead in the 12-pin plug,
- Check for 24v between SECl and'SEC2, If no voltage is
present, check the transformer.
- Check for burn traces or burnt components. If bum spots arc
present, replace board.
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