Application
These two-stage controls are designed to cover
a broad range of general purpose operating
temperature control applications in the
refrigeration, air conditioning, and heating fields.
Two SPDT switches permit independent control
circuits. Each switch may be wired for “open high”
or “close high” action, as required, providing
automatic changeover on heating-cooling or
similar applications. Models are available with
narrow differential on each switch. A jumper
across the “common” terminals is supplied as a
standard feature. Models are available with fixed
or adjustable interstage differential.
Important: A28 Series two-stage temperature
controls are intended to control equipment under
normal operating conditions. Where failure or
malfunction of an A28 temperature control 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)
intended to warn of or protect against failure or
malfunction of an A28 temperature control must
be incorporated into and maintained as part of the
control system.
Operation
Figure 8 illustrates the operation of an A28 Series
control calibrated for cooling applications. On a
temperature increase to the dial setting, the circuit
between R and Y of the low stage switch (RY
L
)
closes.
Simultaneously, the circuit between R and B (RB
L
)
opens. On a further increase in temperature, the
high stage switch operates and closes RY
H
while
opening RB
H
. The reverse sequencing takes place
on a temperature fall.
Installation
Follow equipment manufacturer’s instructions if
provided. If instructions are not provided, proceed
as follows:
A28 Series Two-Stage Temperature Controls with NEMA 1 Enclosure
Installation Guide
Part No. 996-318, Rev. E
Issue Date: May 2022
Risk of Electrical Shock.
Disconnect the power supply
before mounting and wiring to prevent possible
electrical shock. On multiple circuit units, more
than one circuit may have to be disconnected.
Mounting
Controls are normally mounted to a surface
through holes in the back of the case.
Important: On rough mounting surfaces use the
top two mounting holes only. When these controls
are mounted on an uneven surface using screws in
all four holes, the case can be twisted enough to
affect the control’s calibration and operation.
For closed tank applications without well assembly,
Part FTG13A-600R packing nut assembly may be
supplied. See Fig.4 for sequence of installation.
Place the parts over support tube section of the
element and place the bulb in the tank. Ensure the
tank is drained so the liquid level is below tank
opening.
Figure 1: Interior view showing high stage (left)
and low stage (right) switches
Tighten the 1/2 in. NPT adapter. Screw packing
nut into adapter with the retaining washers and
packing in place as shown.
Risk of Personal Injury.
In closed tank applications,
relieve any system pressure before loosening or
attempting to replace an existing bulb well.
To install models supplied with a bulb well, first
install the bulb well into the tank opening. Remove
bushing from the bulb well and slide the bushing
over capillary.
Place the bulb and bushing into the well. Push
bulb into position in bottom of the well. Tighten
set screw in end of the adapter to hold bulb in
position. See Fig. 5 for bulb well installation.
Figure 2: A28 control
Important: Do not dent or deform the sensing
bulb of this control. A dent or deformation will
change the calibration and cause the control to
cycle at a temperature lower than the dial setting.
When the bulb mounting clip is used to mount
the bulb near refrigerant tubing, be sure the sheet
metal screw does not pierce the tubing.
Wiring
Risk of Electrical Shock.
Disconnect the power supply
before mounting and wiring to prevent possible
electrical shock. On multiple circuit units, more
than one circuit may have to be disconnected.
Follow equipment manufacturer’s diagrams if
provided. Wire to conform to local, national, and
regional regulations. Wiring terminals of each
Pennswitch are color coded for convenience and
to simplify wiring. Red is the common terminal;
red to yellow circuit closes on temperature
increase, red to blue circuit opens on temperature
increase. Use copper conductors only.
Use terminal screws furnished (8-32 x 1/4 in.
binder head). Do not substitute screws of a
different size.
Figure 3: Style 1 swaged bulb with support tube
for clamp-on or closed tank applications
Figure 4: Part number FTG13A-600R packing nut
assembly. Use with Style 1 bulb with support tube
for direct immersion applications
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