Gas Heat Troubleshooting Guide - York 20 Series Installation Manual

349215-JIM-B-1008
default. They can be checked by local distributors.
For units with factory installed economizers, the
UCB is programmed to lock out compressor opera-
tion when the LAS set point is reached.
For units without factory installed or with field
installed economizers, the UCB allows compressor
operation all the time. This programming can be
checked or changed by the local distributor.
14. If none of the above corrected the error, test the
integrity of the UCB. 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 HEAT TROUBLESHOOTING GUIDE

Troubleshooting of components may require
opening the electrical control box with the
power connected to the unit. Use extreme
care when working with live circuits! Check
the unit nameplate for the correct line voltage
and set the voltmeter to the correct range
before making any connections with line termi-
nals.
For troubleshooting of optional VFD, discon-
nect all power to the drive. Be aware that high
voltages are present in the drive even after
power has been disconnected. Capacitors
within the drive must be allowed to discharge
before beginning service.
When not necessary, shut off all electric power
to the unit prior to any of the following mainte-
nance procedures so as to prevent personal
injury.
Johnson Controls Unitary Products
Label all wires prior to disconnection when ser-
vicing controls. Wiring errors can cause
improper and dangerous operation, which
could cause injury to person and/or damage
unit components. Verify proper operation after
servicing.
To find the Btu input, multiply the number of
NOTE:
cubic feet of gas consumed per hour by the
Btu content of the gas in your particular locality
(contact your gas company for this information
- it varies widely from city to city.).
The furnace may shut down on a high tem-
perature 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.
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" position).
1. Place the thermostat fan switch in the "ON" posi-
tion. 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. For
units with VFD, check that line voltage is being
supplied to the M3-Auxiliary contacts. 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 protec-
tion. Cancel any thermostat calls and set the fan
switch to "AUTO", wait for the internal overload to
reset. Test again when cool.
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