STEP
ACTION
YES
NO
GO TO
26
Is 115-vac across the transformer leads?
27
25
27
Replace the transformer.
18
28
Is 24-vac across W/W1 and C
OM
-24V on the variable speed
furnace control?
30
29
29
You have a defective thermostat, or a break in wiring be-
tween thermostat and furnace. Fix problem.
18
30
Disconnect all thermostat leads from the thermostat termi-
nal block and jumper R to W/W1.Does the furnace respond
to the call for heat?
31
25
31
You have an incompatible thermostat. Do any of the follow-
ing:
1. Wire the thermostat C terminal to C
OM
-24V.
2. Isolate the W/W1 input with a relay.
3. Install ballast resistor across W/W1 and C
OM
-24V.
4. Replace the thermostat with a compatible model.
18
RAPID FLASHING AMBER LED - Indicates line voltage polarity is reversed, or the transformers are out of phase in twinned units.
STEP
ACTION
YES
NO
GO TO
1
Is this furnace twinned with another furnace?
7
2
2
Remove blower access panel and depress door switch. Use
a piece of tape to hold switch closed.
3
3
Is 115-vac across NEUTRAL-L2 and chassis ground?
4
6
4
Line voltage polarity is reversed. Fix problem.
5
5
Go to page number indicated in Index for CLEANUP AND
START-UP INSTRUCTIONS.
INDEX
6
Replace the variable speed furnace control.
5
7
Remove blower access panels and depress door switch in
each unit. Use tape to hold switches closed.
8
8
Is the AMBER LED status light blinking rapidly in only one
of the twinned units?
9
16
9
Are the fuses, breakers, or manual disconnects to the prob-
lem unit correctly set?
11
10
10
Fix problem.
5
11
Are the Auxiliary Limit switches properly set?
12
10
12
Do you have 115-vac across L1 and NEUTRAL-L2 in the
problem unit?
13
15
13
Do you have 24-vac across SEC-1 and SEC-2 in the prob-
lem unit?
6
14
14
Replace the transformer.
5
15
Turn power off to both units. Check continuity of power
leads and door switch in the problem unit. If necessary re-
pair power leads and/or replace door switch in the problem
unit.
5
16
Check the furnace circuit breaker location in the service
panel.
On single-phase (residential) systems, each furnace circuit
breaker should be located directly across from each other in
service panel, or each furnace circuit breaker should be lo-
cated on the same side of service panel, but must skip 1
space to be connected to the same leg of the 1-phase
power supply.
On 3-phase (commercial) systems, each furnace circuit
breaker should be located directly across from each other in
service panel, or each furnace circuit breaker should be lo-
cated on the same side of service panel, but must skip 2
spaces to be connected to the same leg of the 3-phase
power supply.
17
17
Check the 115-vac power lead connections at the variable
speed furnace control of each furnace. The BLACK lead
goes to L1 and the WHITE lead goes to NEUTRAL-L2.
18
18
Check the 115-vac transformer lead connections at the vari-
able speed furnace control of each furnace. The BLACK
lead goes to L1 and the WHITE lead goes to NEUTRAL-L2.
19
19
If the circuit breaker location and the 115-vac wiring is cor-
rect reverse the transformer secondary lead connections
SEC-1 and SEC-2 in the MAIN furnace.
5
11