Johnson Controls RLY13A-600R, RLY13A-602R, RLY13A-603R, RLY13A-608R, RLY13A-609R Series Manual

P28 and P128 Series Lube Oil Controls

with Built-in Time Delay Relay

The P28 and P128 Series Lube Oil Controls provide
dependable and economical oil pressure cut-out for
pressure-lubricated refrigeration compressors. The
field-adjustable pressure differential of these controls
provides compressor operation according to the
manufacturer’s specifications. The P28 and P128
controls operate by measuring the net lube oil
pressure and de-energizing the compressor if the
pressure falls below the differential setpoint.

Manual or automatic reset models are available with
factory set and sealed time delays of 30, 45, 60, 90,
or 120 seconds (all time delays may not be available
on all models). The P128 is the same control as the
P28 but with 1/4 inch male flare pressure connections.

Master Catalog 125

Pressure Controls Section P

Product/Technical Bulletin P28

Issue Date 0498

Figure 1: P128AA

Features and Benefits

❑

Built-in Time Delay Relay
with Ambient Compensation

❑

Trip-free Manual Reset Provides manual reset that cannot be overridden

❑

Replaceable Time Delay
Relay Assembly

❑

Available with Runlight and
Alarm Terminals

Minimizes timing fluctuations due to temperature
variations

by pressing and holding the reset button

Allows easy field replacement of the time delay
relay and terminal board

Allows the control to be wired for normal oil
pressure runlight signals and shutdown alarm
circuits for remote monitoring of oil pressure
status

© 1998 Johnson Controls, Inc.

Part No. 24-7664-605, Rev. A
Code No. LIT-125420

1

ntroduction

I

!

WARNING: Personal injury hazard. All

P28 and P128 controls are
designed as lubrication
protection controls. Failure of
the P28 or P128 could allow
the refrigeration compressor
to be damaged in a way that
may not be apparent upon
visual inspection. Follow
proper procedures and the
compressor manufacturer’s
instructions, as well as any
warning signs on or around
the equipment, when
discharging and
disassembling the
compressor.

Environmental damage
hazard. If leakage of sensed

media (such as refrigerant or
oil) can be harmful to the
environment, or hazardous in
any way, user must provide
for proper containment.

The P28 and P128 controls measure the net oil
pressure available to circulate oil throughout a
pressure-lubricated refrigeration system. The net oil
pressure is the difference between the oil pressure
at the pump discharge and the refrigerant pressure
in the compressor crankcase.

Example: If the oil pressure pump discharge reading

is 90 psi (621 kPa) and the crankcase
pressure is 70 psi (483 kPa), the net oil
pressure is 20 psi (138 kPa).

The P28 and P128 have a built-in time delay relay.
This relay allows the oil pressure to build up for the
time delay period before the compressor trips. This
also prevents nuisance lockouts due to intermittent
loss of oil pressure. The time delay relay is a
“trip free” device. The manual reset cannot be
overridden by pressing and holding the reset button.

Manual reset models are available with time delays
of 30, 45, 60, 90, or 120 seconds. Automatic reset
models are available with a 90-second time delay.
The time delay relay is compensated to minimize the
effect of ambient temperature variations. However,
the time delay relay will be affected by voltage
variations.

Dimensions

Figure 2: P28 or P128 Dimensions (in./mm)

peration

O

When the compressor starts, the timer is energized
because the net oil pressure of the system is zero.
During normal operation, the net oil pressure should
build up to the pressure switch’s cut-out setting
(scale setting) plus the switch differential (3 to 5 psi
[21 to 34 kPa]) within the required time delay,
causing the time delay relay to de-energize.

If the net oil pressure does not rise to the cut-out
pressure setting plus the switch differential within the
required time delay, the time delay relay trips and
stops the compressor.

If the net oil pressure drops below the cut-out
pressure setting during the compressor’s run cycle,
the time delay relay energizes. If the net oil
pressure returns within the time delay, the time
delay relay de-energizes and the compressor
continues to operate normally. If the net oil pressure
does not return within the time delay, the control
shuts down and locks out the compressor.

2 P—P28 and P128 Series Lube Oil Controls with Built-in Time Delay Relay Product/Technical Bulletin

Example: Net oil pressure (oil pump pressure minus

crankcase pressure) required to the
bearings is 9 psi (62 kPa). The control
scale setting should be 9 psi (62 kPa).
The switch differential is 5 psi (34 kPa).
Upon initial start of the compressor, the
time delay relay energizes. If the net oil
pressure does not build up to 14 psi
(97 kPa), or the scale setting (9 psi) plus
the switch differential (5 psi), during the
time delay, the control breaks the circuit to
the compressor. If the pressure of 14 psi
(97 kPa) is reached during the time delay,
the time delay relay de-energizes and the
compressor continues to operate
normally.

nstallation

I

Mounting

Pressure Connections

!

CAUTION: Equipment damage hazard.

●

Avoid sharp bends or kinks in the
capillary or tubing to avoid damage to
the capillary.

●

Coil and secure excess capillary or
tubing. Because harmonic vibration
can break the capillary or tubing,
some slack must be provided.

●

Do not allow the capillary or tubing to
rub against metal surfaces where
friction can cause damage.

●

When using a control with
1/4 in. / 6.4 mm tubing, a pulsation
damper must be used. Pulsation can
cause excessive wear and damage
the control.

!

CAUTION: Equipment damage hazard.

●

A P28AN or P28DN control used for
ammonia service must be mounted
separately from the electrical cabinet.
An ammonia leak could damage the
electrical circuitry.

●

Do not use Johnson Controls/Penn
Ecosafe® hose tubing in applications
with ammonia or other corrosive
refrigerants. Corrosion could cause
tube breakage and refrigerant
leakage.

●

Use only the mounting screws
supplied with the control. Damage to
internal components may occur if
other screws are used.

The P28 and P128 controls are not position
sensitive and can be mounted in any position.

Use the two mounting screw holes located on the
back of the control case to mount the control directly
to a wall or panel board. Mount the control so that
the pressure connections on the bellows are above
the crankcase liquid level of the equipment being
controlled.

Note: When mounting the control to a

compressor is required, a mounting bracket
(Part No. 271-51) is available.

1. Purge all tubing and lines before connecting the
pressure control.

2. Connect the oil pressure line pump discharge to
the pressure connector labeled “OIL.”

3. Connect the crankcase pressure line to the
pressure connector labeled “LOW.”

4. Coil and secure excess capillary or tubing to
avoid vibration.

Wiring

!

WARNING: Shock hazard. Disconnect

all power supplies before
making wiring connections to
avoid electrical shock or
damage to the equipment.

●

Make all wiring connections using copper
conductors only.

●

Wire in accordance with National Electric Code
and local regulations. For maximum electrical
rating of the control, see the label inside the
control cover.

●

Use the terminal screws furnished (8-32 x 1/4 in.
binder head). Substitution of other screws may
cause faulty connections.

See Figures 3 through 10 for typical wiring diagrams
or refer to the compressor manufacturer’s
specifications.

P—P28 and P128 Series Lube Oil Controls with Built-in Time Delay Relay Product/Technical Bulletin 3