ICP 9MAC/E series Troubleshooting manual - page 25
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4. MEDIUM TO LOW RANGE INPUT TRANSITION – When transitioning to a low range input the medium pressure switch MPS should
open when the PSR relay is energized to open the NC contact. However if the PSR relay contact remains closed and the medium pressure
switch MPS is made the modulating furnace control begins flashing status code 9and continues to operate at the desired low range input.
After the call for heat is satisfied and the blower off-delay is completed the modulating furnace control will stop displaying status code 9.
- HIGH RANGE INPUT OPERATION (72% - 100% OF MAXIMUM HEAT)
1. PREPURGE - If the medium pressure switch MPS does not make within 45 seconds after the low pressure switch LPS made the
modulating furnace control begins flashing status code 9, shuts unit down, waits 2 minutes, stops flashing status code 9, and restarts
heating cycle.
If medium pressure switch MPS opens before ignition, the modulating furnace control ramps inducer RPM up until the medium pressure
switch MPS remakes. When the medium pressure switch MPS remakes the modulating furnace control continues heating cycle. If
medium pressure switch MPS does not remake within 45 sec after opening, the modulating furnace control starts flashing status code 9,
shuts unit down, waits 2 minutes, stops flashing status code 9, and restarts heating cycle.
The high pressure switch HPS is ignored until ignition occurs.
2. MEDIUM TO HIGH RANGE INPUT TRANSITION - If the medium pressure switch MPS opens while transitioning to a high range
input, the modulating furnace control ramps inducer RPM up until the medium pressure switch MPS remakes. When the medium pressure
switch MPS remakes the modulating furnace control continues heating cycle. If medium pressure switch MPS does not remake within 45
sec after opening, the modulating furnace control starts flashing status code 9 and shuts unit down. After the blower off-delay is completed
the modulating furnace control will stop displaying status code 9 and if there is a call for heat, begin a new heating cycle.
If the high pressure switch HPS opens or failed to make within 30 sec after starting the transition, the modulating furnace control ramps
inducer RPM up until the high pressure switch HPS makes. If the high pressure switch HPS fails to make after an additional 45 sec, the
modulating furnace control starts flashing status code 9and shuts unit down. After the blower off-delay is completed the modulating
furnace control will stop displaying status code 9 and if there is a call for heat, begin a new heating cycle.
3. STEADY-STATE - If the high pressure switch HPS opens the modulating furnace control ramps inducer RPM up until the high pressure
switch HPS remakes. When the high pressure switch HPS remakes the modulating furnace control continues the heating cycle. If high
pressure switch HPS does not remake within 45 sec after opening, the modulating furnace control starts flashing status code 9 and shuts
unit down. After the blower off-delay is completed the modulating furnace control will stop displaying status code 9 and if there is a call
for heat, begin a new heating cycle.
4. HIGH TO MEDIUM RANGE INPUT TRANSITION - If the medium pressure switch MPS opens while transitioning to a medium range
input, the modulating furnace control ramps inducer RPM up until the medium pressure switch MPS remakes. When the medium pressure
switch MPS remakes the modulating furnace control continues heating cycle. If medium pressure switch MPS does not remake within 45
sec after opening, the modulating furnace control starts flashing status code 9 and shuts unit down. After the blower off-delay is completed
the modulating furnace control will stop displaying status code 9 and if there is a call for heat, begin a new heating cycle.
5. OTHER TRANSITIONS - If the modulating furnace control is transitioning from low to high range input the modulating furnace control
will first transition from low to medium range input and then transition from medium to high range input. If the modulating furnace
control is transitioning from high to low range input the modulating furnace control will first transition from high to medium range input
and then transition from medium to low range input.
STEP
ACTION
YES
NO
GO TO
1.
Turn 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 power on and depress door switch. Use a piece of tape to hold switch closed.
3
3.
Put setup switch SW4-2 into the ON position, and jumper R and W/W1 thermostat terminals.
4
4.
Wait 90 seconds before proceeding to the next step.
5
5.
Is status code 9 flashing?
9
6
6.
Is a different status code flashing?
7
34
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.
Is 24-vac across GRAY wire on the medium pressure switch MPS and C
OM
-24V on
modulating furnace control?
15
10
10.
Is 24-vac across connector terminal PL1-12 and C
OM
-24V on modulating furnace control?
11
13
11.
You have an open wire or bad terminal on the GRAY wire from the modulating furnace
control to the medium pressure switch MPS.
12
12.
Repair or replace wire harness.
8
13.
Replace the modulating furnace control.
8
14.
You have excessive restriction in the vent pipe. Also, check for proper vent sizing for
installation.
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