Troubleshooting Pcb - Bryant SM03-4 Service Manual

TYPE
CONNECTION
Heater
Connection
3. HP-EFF—provides same airflow for heating and cooling
modes (approximately 350 CFM/ton).
The factory setting is AC. (See Fig. 24.)
D. AC/HP CFM Adjust
Select low, nominal, or high airflow. To provide any of these
airflows, AC/HP ADJUST select must be moved to NOM position.
The factory selection is NOM. The adjust selections HI/LO will
regulate airflow supplied for all operational modes, except non-
heat pump heating modes, +15 percent and -10 percent respec-
tively. The adjust selection options are provided to adjust airflow
supplied to meet individual installation needs for such things as
noise, comfort, and humidity removal. (See Fig. 24.)
E. AC/HP Time Delay
Select desired time delay profile. Four motor operation delay
profiles are provided to customize and enhance system operation.
(See Fig. 24.) The selection options are:
1. The standard 90 sec off delay (factory setting 0/90).
2. No delay option used for servicing unit or when a thermo-
stat is utilized to perform delay functions (0/0).
3. A 30 sec on/90 sec off delay profile used when it is
desirable to allow system coils time to heat up/cool down
prior to airflow. This profile will minimize cold blow in
heat pump operation and could enhance system efficiency
(30/90).
4. ENH, enhanced selection provides a 30 sec on/150 sec at 70
percent airflow and no off delay.
F. Continous Fan
Select desired Continuous fan profile LO, MED, or HI. Airflow are
provided to customize and enhance the continous fan functions.
(See Fig. 24.) The possible selections are:
1. LO—provides 50% of Y/Y2 Cool airflow.
2. MED—provides 65% of Cool airflow (71% on 006 model).
3. HI—provides 100% of Cool airflow.
The factory setting is LO.
NOTE: If applied to two-speed unit, do not select continuous fan
as high since LO speed cooling will also run at HIGH airflow and
insufficient dehumidification may result.
XIII. TROUBLESHOOTING PCB
Use Fig. 25 and 26 and Tables 7 and 8 as guides in troubleshooting
PCB unless otherwise noted.
A. If Fan Will Not Turn On From Thermostat:
IF THERE IS NO HIGH VOLTAGE TO MOTOR:
1. Check connection of 12-pin plug from heaters to receptacle.
This supplies power to transformer and motor. Be sure plug
is connected properly.
TABLE 8—CONNECTIONS AND CONNECTOR (FK4C)
TYPE
PIN NO.
CONNECTOR
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
12-Pin
Pin 7
Pin 8
Pin 9
Pin 10
Pin 11
Pin 12
—32—
DESCRIPTION
Common to screw terminal G
Common to screw terminal Y/Y2 through diode D3
Common to Y1 through diode D2
Common to W2 screw terminal
Common to W2 screw terminal
Common to screw terminal W1 screw terminal
Common to W1 screw terminal
R 24VAC
Common to transformer C
Common to transformer C
Common to transformer C
Common to DH screw terminal
2. Check power leads L1 and L2. If these are not receiving
power, system cannot function.
IF MOTOR 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. 24 and
26.)
2. Check low-voltage fuse shown in Fig. 24. 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.
c. Check sequencers for excessive current draw.
d. Check wiring of heaters. If a heater is miswired, fuse
may blow. If a heater is miswired, correct miswiring.
3. Check yellow and black wire connections on primary side
of transformer. If they are not connected properly, low-
voltage transformer 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.
B. 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 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 fan coil has power applied to it.
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