Electric Heater Function And Troubleshooting - Carrier FA4ANF Service Manual

3. Check power leads L1 and L2. If these are not receiving
power, the system cannot function.
If the PCB has high voltage applied to it:
1. Check the low-voltage transformer leads, R and C. Make sure
they are wired to the correct locations. Note that Fig. 13 shows
wiring of the HK61GA001 board.
2. Check the output voltage of the secondary side, R and C, of
the transformer. If the circuit board is a HK61GA003, make
sure the ground strap is in place from C to the bracket. This
strap must be in place to complete the 24-v circuit. Make sure
the transformer output is around 24-v ac. If the transformer
output is zero-v ac and the transformer is receiving the correct
input voltage (208-v or 240-v), then the transformer needs to
be replaced with the recommended transformer. If the trans-
former output is 24-v ac, then proceed to 3 and 4.
3. Check the low-voltage fuse shown in Fig. 6 and Fig. 7. If the
fuse is blown, replace it. The transformer cannot supply power
to the board with the fuse blown or loose. If the fuse blows
when the unit has power applied to it, the system most likely
has 1 of the following problems:
a. If the transformer is shorting out, check the wiring of the
transformer.
b. The maximum load on the transformer is 40 VA. If the load
on the transformer is excessive, the low-voltage, 5-amp
fuse will blow to protect the transformer. If the load
exceeds the VA rating of the transformer, a larger VA rated
transformer needs to be installed. Check the sequencers for
excessive current draw.
c. Check the wiring of the heaters. If the heater is miswired,
the fuse may blow. Check the diodes shown in Fig. 14 for
signs of overheating. If the heater is miswired, correct the
miswiring.
4. Check the T1, T2, and T3 connections on the primary side of
the transformer. If they are not connected properly, the
low-voltage terminal board cannot supply the 24-v signal to
energize the fan relay. If the transformer is receiving the
correct primary voltage but is not outputting the correct
secondary voltage, the transformer needs to be replaced.
IF THE ELECTRIC HEAT STAGES WILL NOT TURN ON
BUT THE FAN WILL TURN ON:
1. Check the wiring of the sequencer. Pay particular attention to
the high and low-voltage wiring of the sequencers.
2. Check the plug wiring to make sure that it is wired correctly.
3. Check the voltage to the sequencer; sequencer number 1
receives a 24-vac signal. If it is receiving the correct voltage,
check to see if the sequencer is closing. If the sequencer is not
closing but is receiving the correct voltage, replace the
sequencer. If the sequencer is closing, check the high-voltage
wiring as discussed in 1 and 2.
IF THE ELECTRIC HEAT AND THE FAN WILL NOT TURN
ON:
If there is no high voltage to the PCB:
1. Check the plug connection. This brings power to the PCB
transformer and the fan. Make sure the plug is connected
properly.
2. Check sequencer number 1 and the plug wiring. The yellow
wire should be connected to pin number 9 of the plug and the
limit switch. The black wire should be connected to pin
number 7 of the plug and to sequencer number 1.
3. Check incoming high-voltage power leads. If these are not
receiving power, the system cannot function.
If the PCB has high-voltage applied to it:
1. Check the low-voltage transformer leads, R and C. Make sure
they are wired to the correct location. The unit will not
function without proper connections.
2. Check the output voltage of the secondary side, R and C, of
the transformer. If the circuit board is an HK61GA003, make
sure the ground strap is in place from C to the bracket. This
strap must be in place to complete the 24-v circuit. If the
transformer output is zero-v ac, refer to "If the PCB has high
voltage applied to it" in column 1, numbers 3 and 4.
IF THE TRACES ARE BURNT OFF THE BACK OF THE PCB:
Usually whenever there is a trace blown on the PCB it means
either there has been a high-voltage short or high voltage has been
applied to the low-voltage circuit. This can be prevented by
making sure the PCB is wired correctly before the PCB has power
applied to it.
IF THERE ARE BLOWN DIODES:
1. If diodes a and b are blown, it is probable the electric heater
plug was miswired. Correct the miswiring. It should be noted
the board will need to be replaced if the diode indicated is bad.
2. If any of the c diodes are blown, the fan is miswired to 1 of the
low-voltage terminals, AUX1 or AUX2. Check to make sure
that the fan leads are connected to the proper terminals as
shown in Fig. 13. If the fan is connected properly, make sure
that no other high voltage is applied to the AUX terminals.
THE PCB FUSE KEEPS BLOWING:
When the low-voltage fuse blows, it means the transformer would
have just blown if the fuse had not been in the circuit to protect it.
The fuse usually blows when there is a high current draw on the
transformer, high voltage applied to the low-voltage circuit, or a
direct secondary short. When there is a high current draw on the
transformer, it is most likely because the transformer has been
shorted or the system is trying to draw more VA than the
transformer is rated for. When the fuse blows because of high
voltage, the system has mixed high- and low-voltage signals.
1. Check the transformer and thermostat wiring as shown in Fig.
11. Make sure the transformer is not shorting out by the
thermostat wires being miswired.
2. Check the wiring of the sequencers as shown in Fig. 13. Make
sure the low-voltage and the high-voltage wiring are con-
nected to the proper sequencers.
3. Check the VA draw on the transformer. If the VA draw is
more than the VA rating of the transformer, the fuse will blow.
If this is the case, replace the transformer with 1 that has a
higher VA rating and meets system specifications.
THE FAN RUNS CONTINUOUSLY:
1. If the PCB has no low-voltage power, check the blue and
black fan leads. These may be switched at the sequencer.
2. If the PCB has low-voltage power, check the fan relay to see
if it is opening and closing. It may be stuck in the normally
closed position due to debris in the relay.
3. See Service Manager Bulletin (SMB) 92-3.
TRANSFORMER FAILURE:
1. Check the 208-v and 240-v taps connected to T1, and T3.
They may be miswired.
ELECTRIC HEATER FUNCTION AND
TROUBLESHOOTING
This section describes KFA, KFB, KFC, and KFD series electric
heaters in exclusion of Smart Heat by examining the functional
operation of these heaters.
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