Pressure Switches - Bryant R-22 Application Manual And Service Manual

OPERATING
TIME
T1
_
T2
BLK DENOTES CLOSED CONTACTS
HN67ZA002
Y YEL
TERMINAL
BOARD
CONNECTION
11
Fig. 18—Wiring for Single-Pole Contactor
thereby improving the efficiency of the system. The sequence of
operation is that on closure of the wall thermostat and at the end of
a fixed on-delay of 1 sec, the fan relay is energized. When the
thermostat is satisfied, an off-delay is initiated. When the fixed
delay of 90 ± 20 sec is completed, the fan relay is de-energized and
fan motor stops. If the wall thermostat closes during this delay, the
5 MIN
Fig. 16—Cycle-Protector Sequence
CUT YELLOW WIRE
BETWEEN CONTACTOR AND
LOW-PRESSURE SWITCH
SAFETY
YEL
CONTROL
YEL
T1
Fig. 17—Cycle-Protector Wiring
DSV
CH
21
A91426
SEC
T1
_
T2
BLK DENOTES CLOSED CONTACTS
HN67PA025, HN67ZA003, HN67ZA008
A91436
YEL
VIO
LOGIC T3
T2
TDR is reset, and the fan relay remains energized. The TDR is a
24v device that operates within a range of 15 to 30v and draws
about 0.5 amps.
If the blower runs continuously instead of cycling off when the fan
switch is set on AUTO, the TDR is probably defective and must be
replaced.
VII. PRESSURE SWITCHES
Pressure switches are protective devices wired into control circuit
(low voltage). They shut off compressor if abnormally high or low
pressures are present in the refrigeration circuit. Depending on unit
model, you may find a low- and/or high-pressure switch in system.
LOW-PRESSURE SWITCH
Located on suction line of condensing unit only, the low-pressure
switch protects against low-suction pressures caused by such
events as loss of charge, low airflow across indoor coil, dirty
filters, etc. It opens on a pressure drop at about 27 psi. If system
pressure is above this, switch should be closed. To check switch,
turn off all power to unit, disconnect leads on switch, and apply
ohmmeter leads across switch. You should have continuity on a
good switch. Because these switches are attached to refrigeration
system under pressure, it is not advisable to remove this device for
troubleshooting unless you are reasonably certain that a problem
exists. If switch must be removed, remove and recover all system
charge so that pressure gages read 0 psi.
—17—
3 OPERATING
TIME
C BRN C
TERMINAL
BOARD
CONNECTION
BLK
5 MIN
A91437
A88415