Installation Sheets Manual 121
Pressure Controls Section
Technical Bulletin P70
Issue
Date
0784
© 1984 Johnson Controls, Inc.
1
Code No. LIT-121455
Part No. 996-34
, Rev. B
P70 Series MICRO-SET
TM
Pressure Controls
for Refrigeration and Air Conditioning,
4-Wire, 2-Circuit Contact Block
Application
P70 single and dual function
pressure controls are used in
commercial air conditioning and
refrigeration applications. The
load-carrying contacts provide
direct control of A.C. motors
within the control’s rating. (See
cover label for the electrical
rating.)
The controls can be used with R-
12, R-22, R-500, or R-502
refrigerants. Specific models for
ammonia applications are also
available. The MICRO-SET
construction of low pressure
controls and low side of dual
models permits differentials to a
minimum of 5 psi (34 kPa).
!
WARNING: On ammonia
applications, the ammonia
P70 pressure control must
be mounted separately from
the electrical cabinet.
All Series P70 controls are
designed for use
only
as
operating controls. Where an
operating control failure would
result in personal injury and/or
loss of property, it is the
responsibility of the installer to
add devices (safety, limit
controls) that protect against, or
systems (alarm, supervisory
systems) that warn of control
failure.
Certain models of the Series P70
controls are supplied as
pressure limiting devices for
refrigeration or conditioning
equipment. Contact Control
Products Division, Johnson
Controls, Inc. for specific model
identification for refrigeration
pressure limiting applications.
Operation
These controls are available with
either main contacts (LINE-M2)
CLOSE high - OPEN low, or
main contacts (LINE-M2) OPEN
high - CLOSE low contact action.
The controls have a four-wire,
two-circuit contact block that
operates from a pressure
actuated bellows.
The controls have a single
“sight-set” calibrated scale which
shows cutout setting and the
differential. Adjustments can be
made readily without removing
the control cover.
Installation
Mounting
Mount the control on a flat
surface or panel board by two
screws or bolts through the holes
in the back of the case. The
control should be mounted
above the element connections
to provide drainage from the
sensing elements. The pressure
connection on the bellows should
be above the liquid level of the
equipment on which the control
is used. This reduces possible
accumulation of foreign matter
inside the bellows.
!
CAUTION: Do not mount
the control in a position
where dirt, sediment, or oil
will affect the operation of
the control.
Universal mounting bracket
No. 271-51 is available, if
required. (
Note:
When using
any bracket, use only mounting
screws supplied with the control
to prevent damage to internal
components.)
General Instructions
1. Avoid sharp bends or kinks
in the capillary tubing.
2. Be sure pressure controls
installed on ammonia
systems are built for
ammonia service.
3. Purge all tubing and lines
before connecting pressure
controls.
4. Make sure the control is not
installed on equipment to
handle a load in excess of
the switch’s electrical rating.
5. Coil and secure excess
capillary length to avoid
vibration but allow some
slack in the capillary to
avoid “violin string” vibration
which can cause tubing to
break. Do not allow tubing
to rub against metal
Fig. 1 -- Interior view of
MICRO-SET single function
pressure control.
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