Specifications

035-17377-000 (0201) REV A
62 Unitary Products Group
For units with economizers
:If 24 volts is present at the Y1
“OUT” terminal, check for 24 volts at the Y1 “ECON” termi-
nal. If 24 volts is not present, check for loose wiring from
the Y1 “OUT” terminal to the Mate-N-Lock plug, a poor
connection between the UCB and economizer Mate-N-
Lock plugs, loose wiring from the Mate-N-Lock plug to the
economizer, back to the Mate-N-Lock plug, and from the
Mate-N-Lock plug to the Y1 “ECON” terminal. The econo-
mizer board may have faulted and is not returning the 24
volts to the Y1 “ECON” terminal even though the econo-
mizer is not providing free cooling. To test the economizer
board, disconnect the Mate-N-Locks and jumper between
the WHITE and YELLOW wires of the UCB’s Mate-N-Lock
plug.
13. The UCB can be programmed to lock out compressor
operation during free cooling and in low ambient condi-
tions. These options are not enabled by default. They can
be checked by local York distributors.
14. If none of the above corrected the error, test the integrity of
the UGB. Disconnect the C1 terminal wire and jumper it to
the Y1 terminal. DO NOT jump the Y1 to C1 terminals. If
the compressor engages, the UCB has faulted.
15. If none of the above correct the error, replace the UCB.
GAS FURNACE OPERATIONS
On calls for heating, the draft motor operates and the furnace
lights but the supply air blower motor does not energize after a
short delay (the room thermostat fan switch is in “AUTO” posi-
tion).
1. Place the thermostat fan switch in the “ON” position. If the
supply air blower motor energizes, go to Step 9.
2. If the supply air blower motor does not energize when the
fan switch is set to “ON,” check that line voltage is being
supplied to the contacts of the M3 contactor, and that the
contactor is pulled in. Check for loose wiring between the
contactor and the supply air blower motor.
3. If M3 is pulled in and voltage is supplied at M3, lightly
touch the supply air blower motor housing. If it is hot, the
motor may be off on inherent protection. Cancel any ther-
mostat calls and set the fan switch to “AUTO”, wait for the
internal overload to reset. Test again when cool.
4. If M3 is not pulled in, check for 24 volts at the M3 coil. If
24 volts is present at M3 but M3 is not pulled in, replace
the contactor.
5. Failing the above, if there is line voltage supplied at M3,
M3 is pulled in, and the supply air blower motor still does
not operate, replace the motor.
6. If 24 volts is not present at M3, check that 24 volts is
present at the supply air blower motor terminal on the
UCB. If 24 volts is present at the UCB terminal, check for
loose wiring between the UCB and M3.
a. If 24 volts is not present at the UCB supply air blower
motor terminal, check for 24 volts from the room ther-
mostat. If 24 volts is not present from the room ther-
mostat, check for the following:
proper operation of the room thermostat (contact
between R and G with the fan switch in the “ON” posi-
tion and in the “AUTO” position during operation
calls), b) proper wiring between the room thermostat
and the UCB, and c) loose wiring from the room ther-
mostat to the UCB.
7. If 24 volts is present at the room thermostat but not at the
UCB, check for proper wiring between the thermostat and
the UCB, i.e. that the thermostat G terminal is connected
to the G terminal of the UCB, and for loose wiring.
8. If the thermostat and UCB are properly wired, replace the
UCB.
9. If the blower motor runs with the fan switch in the “ON”
position but does not run shortly after the furnace has
ignited when the fan switch is in the “AUTO” position,
check the room thermostat for contact between R and G
during “W1” calls.
On calls for heating, the supply air blower operates but the
draft motor does not (the room thermostat fan switch is in the
“AUTO” position).
1. The draft motor has inherent protection. If the motor shell
is hot to the touch, wait for the internal overload to reset.
2. If the motor shell is cold with the room thermostat calling
for heat, check for line voltage at the motor leads. If line
voltage is present, replace the draft motor.
3. If line voltage is not present, check for line voltage on the
ignition control at the “inducer” terminal draft motor relay
(DMR or DMC) contacts in the main control box and check
to see if the (DMR or DMC) is pulled in.
The draft motor runs but the furnace does not light and the
spark ignitor does not spark.
The furnace may shut down on a high temperature
condition during the procedure. If this occurs, the
UCB energize the supply air blower motor until the
high temperature limit has reset. Caution should
be used at all times as the supply air blower may
energize regardless of the room thermostat fan
switch position.