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Status Code 3 + 5
GAS VALVE FAULT - This status code indicates that the modulating gas valve failed to respond to a command from the
modulating furnace control or power to the gas valve electronics was interrupted.
On every cycle after the medium pressure switch MPS makes the modulating furnace control sends a PWM (pulse width modulation) command to
the gas valve GV for a duration of 1 second. Following this the gas valve GV responds back with the PWM command it received for a duration of 1
second. If the PWM response does not match the command sent the modulating furnace control will resend the PWM command up to 5 more times.
After the gas valve sends the PWM response it operates the stepper motor. The stepper motor can be operated for up to 17 seconds if the propane
jumper is installed in the gas valve GV. This worst case time is also dependent on the initial position of the stepper motor, if power was just reset,
and if the initial call for heat after power-up is maximum heat. Generally speaking the stepper motor will only operate for a few seconds or less.
After the stepper motor is done moving the gas valve GV will send a PWM-DONE command to the modulating furnace control. If the gas valve GV
fails to respond back with the PWM command it received or the PWM-DONE command the modulating furnace control will flash status code 3 + 5,
shut the unit down, wait 2 minutes, stop flashing status code 3 + 5, and restart the heating cycle.
The same general operation stated above also applies when the blower motor is turned on or whenever the modulating gas rate is changed. The only
exception is the stepper motor will operate for a few seconds.
Due to these short 1 second command/response bursts it is difficult to troubleshoot the gas valve GV. As a result the COMPONENT TEST mode is
designed to send the command for intermediate gas rate to the gas valve 15 seconds after the COMPONENT TEST is started. The only exception is
the PWM command will only be sent 3 times and you may not get status code 3 + 5 to flash at the end of the COMPONENT TEST.
STEP
ACTION
YES
NO
GO TO
1.
Shut the power off, remove both doors and disconnect communication connector PL7 (if
used) or the R thermostat lead (if used) from the furnace control board.
2
2.
Turn the power on and depress the door switch. Use a piece of tape to hold it closed.
3
3.
Jumper the R and W/W1 thermostat terminals.
4
4.
Observe the operation of the furnace for the next 5 minutes or until fault occurs.
5
5.
Does status code 3 + 5 flash?
9
6
6.
Does a different status code flash?
7
8
7.
Go to page number indicated in the Index for the section covering the status code.
INDEX
8.
Go to page number Indicated in Index for CLEANUP AND START-UP INSTRUCTIONS.
INDEX
9.
Does status code 3 + 5 flash at the start of the cycle before the hot surface igniter would
normally be energized?
10
35
10.
Is 24-vac across RED and GREEN/YELLOW wire at gas valve?
15
11
11.
Is 24-vac across PL8-1 and C
OM
-24V on modulating furnace control?
12
13
12.
You have an open wire or bad terminal on the RED or GREEN/YELLOW wire from the
modulating furnace control to the gas valve GV.
14
13.
Replace the modulating furnace control.
8
14.
Repair or replace the main wire harness.
8
15.
Disconnect jumper wire across R and W/W1 thermostat terminals and wait for the blower to
turn off.
16
16.
Connect a DC voltmeter across terminals PL17-2 YELLOW (+) and PL17-4
GREEN/YELLOW (-). Is there 4-vdc across the YELLOW and GREEN/YELLOW wires?
18
17
17.
Replace gas valve.
8
18.
Check the gas valve PWM input. To do this connect a DC voltmeter across terminals PL17-2
YELLOW (+) and PL17-4 GREEN/YELLOW (-) then run COMPONENT TEST by turning
setup switch SW1-6 ON. In 15 seconds the voltage will drop briefly from 4.0-vdc. The
voltage drop will be several volts or more and will last for about 1 second. If everything is
working properly this will happen once otherwise the voltage will drop briefly 2 more times
while the hot surface igniter is energized.
19
19.
Does the voltage drop briefly 3 times as described in step 18?
27
20
20.
Does the voltage drop briefly at all?
21
23
21.
If the voltage dropped briefly once then the communication between the modulating furnace
control and the gas valve are working properly.
22
22.
Put setup switch SW1-6 in the OFF position. There may be an intermittent connection
between the modulating furnace control and the main wire harness at connector PL8 or
between the main wire harness and the gas valve at connector PL17.
14
23.
Turn power off and put setup switch SW1-6 in the OFF position.
24
24.
Disconnect PL8 from the modulating furnace control and PL17 from the gas valve.
25
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