York 20 Series Installation Manual page 58

349215-JIM-B-1008
between the room thermostat and the UCB, i.e. Y1
to Y1, Y2 to Y2, and c) loose wiring from the room
thermostat to the UCB.
8. If 24 volts is present at the UCB Y1 terminal, the
compressor may be out due to an open high-pres-
sure switch, low-pressure switch, or freezestat.
Check for 24 volts at the HPS1, LPS1, and FS1
terminals of the UCB. If a switch has opened, there
should be a voltage potential between the UCB ter-
minals, e.g. if LPS1 has opened, there will be a 24-
volt potential between the LPS1 terminals.
9. If 24 volts is present at the UCB Y1 terminal and
none of the protection switches have opened, the
UCB may have locked out the compressor for
repeat trips. The UCB should be flashing an alarm
code. If not, press and release the ALARMS button
on the UCB. The UCB will flash the last five alarms
on the LED. If the compressor is locked out, cancel
any call for cooling. This will reset any compressor
lock outs.
While the above step will reset any lockouts,
NOTE:
compressor #1 may be held off for the ASCD.
See the next step.
10. If 24 volts is present at the UCB Y1 terminal and
none of the switches are open and the compressor
is not locked out, the UCB may have the compres-
sor in an ASCD. Check the LED for an indication of
an ASCD cycle. The ASCD should time out within
5 minutes. Press and release the TEST button to
reset all ASCDs.
11. If 24 volts is present at the UCB Y1 terminal and
the compressor is not out due to a protective
switch trip, repeat trip lock out, or ASCD, the econ-
omizer terminals of the UCB may be improperly
wired. Check for 24 volts at the Y1 "OUT" terminal
of the UCB. If 24 volts is present, trace the wiring
from Y1 "OUT" for incorrect wiring. If 24 volts is not
present at the Y1 "OUT" terminal, the UCB must be
replaced.
12. For units without economizers:If 24 volts is present
at the Y1 OUT terminal, check for 24 volts at the
Y1 "ECON" terminal. If 24 volts is not present,
check for loose wiring from the Y1 "OUT" terminal
to the Mate-N-Lock plug, the jumper in the Mate-N-
Lock plug, and in the wiring from the Mate-N-Lock
plug to the Y1 "ECON" terminal.
58
13. For units with economizers: If 24 volts is present at
the Y1 "OUT" terminal, check for 24 volts at the Y1
"ECON" terminal. 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. If nothing is found,
the economizer control may have faulted and is fail-
ing to return the 24-volt "call" to the Y1 "ECON" ter-
minal even though the economizer is not providing
free cooling. To test, disconnect the Mate-N-Locks
and jumper between the WHITE and YELLOW
wires of the UCB's Mate-N-Lock plug. If compressor
#1 energizes, there is a fault in the economizer wir-
ing or the economizer control.
14. The UCB can be programmed to lock out compres-
sor operation during free cooling and in low ambi-
ent conditions. These options are not enabled by
default. Local distributors can test the UCB for this
programming.
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.
15. 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.
16. If none of the above correct the error, replace the
UCB.
On calls for the second stage of cooling, the supply air
blower motor and compressor #1 are operating but
compressor #2 is not (the room thermostat fan switch
is in the "AUTO" position).
1. If installed, check the position of the economizer
blades. If the blades are open, the economizer is
providing free cooling. If the second stage of cool-
ing is requested, following a short delay, compres-
sor #1 will be energized unless it is locked out.
Typically, compressor #2 is energized only during
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