Installation Instructions
A19BAC, A28AA
Issue
Date
0403
®
A19BAC, A28AA Single and Two-Stage Space Thermostats
For Farm and General Purpose Applications
Application
The single-stage A19BAC and the
two-stage A28AA thermostats
incorporate single-pole double-
throw (SPDT) switches for
controlling automatic ventilation or
heating in livestock barns, poultry
houses, milk houses, brooder
houses and other buildings. The 30
to 110
°
F (0 to 43
°
C) and 0 to 140
°
F
(-15 to 60
°
C) temperature ranges
permit use for many space
applications.
IMPORTANT: The single-stage A19
and A28 thermostats are
intended to control equipment
under normal operating
conditions. Where failure or
malfunction of an A19 or A28
thermostat 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 the A19 or A28
thermostat must be
incorporated into and
maintained as part of the
control system.
!
CAUTION:
Risk of
Property Damage.
Do not
install A19 or A28 space
thermostats with general
purpose enclosures in any
type of agricultural
environment defined in NEC
Art. 547 where dust or dust
with water may accumulate or
where corrosive atmospheres
exist. Doing so may cause the
A19 or A28 thermostat to fail
and result in the loss of
temperature regulation and
damage to other property.
Operation
Figs. 4 and 5 illustrate the operation
of the A19. On a temperature
increase, the circuit between R and
Y closes. Simultaneously the R and
B circuit opens.
Figure 6 illustrates the operation of
the A28AA. On a temperature
increase, 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
simultaneously opening RB
H
.
The reverse sequencing takes
place on a temperature fall.
Installation
Mounting
Mount control to a flat surface with
screws through holes provided in
back of frame.
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 thermostat’s
calibration and operation.
Mount the control where it is
exposed to the average
temperature of the controlled space.
Do not mount where it will be
affected by unusual heat or cold,
such as directly over an animal
stall, in sunlight, or on an outside
wall. Avoid locations near a door,
window or hay chute.
Fig. 1 -- Exterior view of Space
Thermostat
IMPORTANT: Do not dent or
deform the sensitive bulb of
this thermostat. A dent or
deformation will change the
calibration and cause the
thermostat to cycle at a
temperature lower than the
dial setting.
Adjustment
Knob adjustment or screwdriver slot
is supplied on the range screw. Dial
pointer is located on adjustment
stop bracket on knob and
screwdriver adjustment models.
Before removing the cover, verify
that all power to the thermostat and
associated equipment is turned off.
!
WARNING:
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.
© 2003 Johnson Controls, Inc.
1
Part No. 996-238, Rev. C
