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2
Note
The controls are intended to control
equipment under normal operating
conditions. Where failure or malfunctioning
of the controls could lead to an abnormal
operating condition that could cause
personal injury or damage to the
equipment or other property, other devices
(limit or safety controls) or systems (alarm
or supervisory systems) intended to warn
of or protect against failure or
malfunctioning of the controls must be
incorporated into and maintained as part of
the control system.
Note
To
facilitate
order
ordering codes have been added to some
commonly used models
Type number matrix
P78LCA
Automatic reset both sides
P78MCA
Automatic reset low side manual
reset high side
P78PGA
Manual reset both sides
P78LCW
Automatic reset both sides
conform DIN32733,PED 97/23CE
P78MCB
Automatic reset low side manual
reset high side conform DIN32733,
PED 97/23CE
P78MCS
Automatic reset low side manual
reset high side conform DIN32733,
PED 97/23CE
P78PGB
Manual reset both sides conform
PED 97/23CE
P78PLM
2 x manual rest HP conform
DIN32733, PED 97/23CE
P78ALA
Dual fan cycling control (2 x SPST
close high)
Adjustment
On most models the range scale indicates the
high switch point (exception: LP side of
P78PGA,P78PGB, here the range scale
indicates the low switching point). To obtain low
switch point deduct differential value from the
high switch point.
Repair and replacement
Repair is not possible. In case of an improperly
functioning control, please check with your
nearest supplier. When contacting the supplier
for a replacement you should state the
type/model number of the control. This number
can be found on the data plate or cover label.
Catalogue Section 6
handling
special
Contact functions
(see also "Type Number Selection" table)
A
Line ~
max. 20 A
LP
LP.
A - C opens on pressure decrease
A - B closes simultaneously
HP.
A - C opens on pressure increase
A - D closes simultaneously
Fig. 1
A
Line ~
max. 20 A
HP
Left side HP. A - C opens on pressure increase
A - B closes simultaneously
Right side HP. A - C opens on pressure increase
A - D closes simultaneously
Fig. 2
Switching action P78ALA
A - D closed
(fan 2 ON)
A - D open
(fan 2 OFF)
A - B closed
(fan 1 ON)
A - B open
(fan 1 OFF)
D
cut-in point
D = diferential per stage (fixed)
Fig.3a
A
Line ~
max. 20 A
HP
Fig. 3b
P78
Issue 03/04/2002
D
C
M
HP
B
B
D
C
M
HP
D
P
pressure
S1
S2
increase
cut-in point
fan 1
fan 2
B
D
HP
M1
M2
© 2002 Johnson Controls Inc.
Order No. PD-P78-E
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