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?
916
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?
614
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
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