Johnson Controls 40 25 TON, Installation Operation & Maintenance

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JOHNSON CONTROLS
5276178-JIM-C-0118
5
The IPU control is designed to be used with tandem
compressors so it identifies the compressors for system
one as 1 A and 1B. Likewise for system 2 they are
identified as 2A and 2B. Since the Series 40 unit uses
individual compressors, in the narrative compressor 1A
is compressor 1, 1B is compressor 2, 2A is compressor 3,
and 2B is compressor 4. Each of the four compressors
has a high and low pressure switch in its refrigerant
circuit. Because of the design of the IPU control the
safeties for compressor 1 and 2 are tied together so that
if either opens both compressors will be shut OFF. The
same arrangement also exists for compressors 3 and 4.
The following safeties comprise the safety circuit:
•
High Pressure Cut Out
•
Low Pressure Cut Out
The above safety circuit supplies a digital 24V signal to
the Unit Controller. The input for compressors 1 and 2
is terminal block TB7 pin 1, the input for compressors
3 and 4 is terminal block TB7 pin 2. If one of the
safeties opens, the signal is lost. When this occurs
the Unit Controller turns off both compressors if one
of the compressors has the fault. The Unit Controller
then records the time it takes for the safety circuit to
reestablish the 24V circuit to the Unit Controller. The
time to reset is displayed in the history buffer and is
identified as
“COMP STATUS (1, 2, OR 3) CLEAR
TIME”
. The length of time it takes to reset is an
indication of which of the safeties opened. If the reset
time is greater than 60 minutes the history buffer will
replace “COMP STATUS (1, 2, OR 3) CLEAR TIME”
with
“COMPRESSOR SYSTEM (1, 2, OR 3) TIME
OUT.”
The safety circuit input is ignored when both compressors
of the system are OFF. If either or both of the compressor
are active and the 24V safety circuit input is lost to the
Unit Controller for two seconds, the Unit Controller
turns off the active compressors for that system. The
compressor system will be made active again when
the safety circuit is reestablished. However, the event
will be stored in the History buffer. During the time
the safety circuit is open the User Interface will display
the following messages:
•
STATUS screen
-
“COMPR SYS # STATUS -
SAFETY TRIP”.
•
COMPRESSOR SYSTEM
#
screen
-
“SAFETY
TRIP”.
•
The HISTORY buffer will store and display the
following -
“COMP # SAFETY TRIP (1 OR 2)”
depending if this is the first or second trip.
If the safety circuit opens three times in a 120-minute
window, the Unit Controller will lock out the compressor
system having the fault and prevent further operation
of that compressor system until the system is manually
reset. The User Interface will display the following
messages:
•
STATUS screen
-
“COMPR SYS # STATUS -
SAFETY LOCKOUT”.
•
COMPRESSOR SYSTEM
#
screen
-
“SAFETY-
LOCKOUT”.
•
The HISTORY buffer will store and display the
following
-
“COMP # SAFETY LOCKOUT”.
SUPPLY AIR TEMPERING
In some installations the ventilation requirements
combined with low outdoor temperature can result in the
Supply Air Temperature dropping below the “SUPPLY
AIR TEMP ACTIVE SP” resulting in an over cooling
of the space. Supply Air Tempering uses the units
heating source to raise the Supply Air Temperature to
an acceptable level.
In order for Supply Air Tempering to be active, the
following items must be programmed into the Unit
Control. Under the PROGRAM key, HEATING
subsection
“HEATING SYSTEM”
must be set to USER
ENABLE. Under the PROGRAM key, COOLING
subsection “SUP AIR TEMPERING” must be set to
USER ENABLE.
The Supply Air Tempering logic will vary depending
on the type of heat installed in the unit. A description
of each of the operating logics follows.
Hot Water and Steam
In order for the Supply Air Tempering to be enabled,
the following conditions must be met:
•
Operating Conditions
- For VAV units the
“SUPPLY AIR TEMP”
must be less than or equal to the
“SUPPLY
AIR TEMP ACTIVE SP” minus 2.5°F for 5
minutes.
- For FlexSys without Bypass the
“MX SUP-