STEP
ACTION
YES
NO
GO TO
56
Continue to observe the furnace operation for 10 minutes.
57
57
Does status code 24 flash after the blower comes on?
58
59
58
The insulation is loose and has shorted against the limit
switch(es).
11
59
Check for loose or torn insulation because it can cause in-
termittent occurrences of status code 24.
45
Status Code 25
MODEL SELECTION OR SETUP ERROR – If status code 25 only flashes 4 times on power-up the variable speed furnace control is
missing its model plug (PL4) and is defaulting to the model selection stored in memory.
This usually indicates one of the following:
1. Model plug (PL4) is missing and there is no valid model stored in permanent memory. This will happen if you forget to install the model
plug (PL4) on a service replacement board.
2. Thermostat call with SW1-1 ON.
3. Thermostat call with SW1-6 ON.
4. SW1-1 and SW1-6 both ON together.
5. Two different furnace models twinned.
STEP
ACTION
YES
NO
GO TO
1
Turn power off, remove blower the blower access panel,
and disconnect R thermostat lead.
2
2
Turn power on and depress door switch. Use a piece of
tape to hold switch closed.
3
3
Does status code 25 flash only 4 times on power-up?
4
6
4
The model plug is missing or invalid but the control will de-
fault to the model stored in memory. The furnace will oper-
ate properly as if the model plug was installed. If you have
the APM program you can confirm the setting in memory.
5
5
Go to page number indicated in Index for CLEANUP AND
START-UP INSTRUCTIONS.
INDEX
6
Is setup switch SW1-1 in the ON position?
7
8
7
Put setup switch SW1-1 in the OFF position.
5
8
Is setup switch SW1-6 in the ON position?
9
10
9
Put setup switch SW1-6 in the OFF position.
5
10
Is this a new service replacement control?
11
13
11
You need to remove the model plug PL4 from the old con-
trol and install it on the new replacement control. Once you
install the model plug the power to the furnace needs to be
reset because the model plug is only read on power-up.
12
12
If the model plug is not available from the old control, refer-
ence the model plug chart on the wiring schematic for the
correct part number. If absolutely necessary you can install
two resistors into the PL4 connection on the control board.
R1 goes across the middle 2 pins and R2 goes across the
outer 2 pins. Reference the model plug chart on the sche-
matic for the correct resistance values. Resistors can be
purchased at a nearby Radio Shack. The resistors need to
be within 10of the stated value. Check with an ohm meter
before installing.
5
13
Is this furnace twinned with another furnace?
14
17
14
Is the MAIN furnace flashing the status code?
15
17
15
Do the furnaces have the same model number on the rating
plate?
18
16
16
Replace one of the furnaces because you cannot twin dif-
ferent size furnaces.
5
17
Replace the variable speed furnace control.
5
18
One of the model plugs is bad. Ohm out each one and re-
place the one that does not match the model plug chart on
the wiring schematic.
5
20
