Operation - Johnson Controls P70 Manual

A
pplication
P70, P72, and P170 controls for low pressure
applications are designed primarily to provide low-side
pressure control on commercial refrigeration and air
conditioning applications.
IMPORTANT: Except for those models listed as
Refrigeration Pressure Limiting
Controls, the P70, P72, and
P170 Series controls for low
pressure applications are
intended to control equipment
under normal operating
conditions. Where failure or
malfunction of the P70, P72, and
P170 pressure 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 malfunction of the P70, P72,
and P170 pressure controls must
be incorporated into and
maintained as part of the control
system.
•
P70A and P170A models with Single-Pole
Single-Throw (SPST) Open-low switch action are
the most popular models, and are typically used
for low pressure cut-out and pump-down control.
•
P70 and P170 models are also available with
SPST Open-high switch action, and are typically
used for capacity control. Models with Single-Pole
Double-Throw (SPDT) or 4-wire, 2-circuit switch
action allow users to install alarm devices or other
control circuits.
•
P72 models have a Double-Pole Single-Throw
(DPST) switch with load-carrying contacts that can
provide direct control of 208-240 V single-phase
motors up to 3 hp, and 208-220 V 3-phase motors
up to 5 hp. Refer to Table 8.
These controls are available in several pressure
ranges and are compatible with most common
refrigerants. They may also be used on air, water, and
other non-corrosive fluid applications. Ammonia
compatible models are also available.
2 P—P70, P72, and P170 Controls for Low Pressure Applications Product/Technical Bulletin
The MICRO-SET option provides fine adjustment of
the differential setting for precision pressure control of
critical low pressure applications.
Some models are available with Limited Knob
Adjustment, which restricts adjustment of the
pressure settings and deters overadjustment or
tampering. See Limited Knob Adjustment.
!
CAUTION: Equipment Damage Hazard.
Ammonia is very corrosive to
copper and brass components.
On ammonia applications, only
ammonia-compatible control
models and pressure
connections must be used. The
pressure control must be
mounted separately from the
electrical cabinet and all
electrical piping sealed to
prevent ammonia from migrating
to electrical components.
The Manual Reset Lockout mechanism does not
allow the pressure control to automatically reset after
the control has cut out, providing shutdown capability
for unmonitored equipment. See Manual Reset

Operation.

NEMA 1 enclosures are standard on most models.
NEMA 3R enclosures are also available.
O
peration
A pressure-actuated bellows on the control is
connected to a pressure tap on the controlled
equipment by a capillary or a field-installed hose
(except ammonia models). The bellows responds to
equipment pressure changes and operates a
snap-action electrical switch.